Content uploaded by Nikolas Hagemann
Author content
All content in this area was uploaded by Nikolas Hagemann on Jul 31, 2019
Content may be subject to copyright.
The use of biochar in animal feeding
Hans-Peter Schmidt
1
, Nikolas Hagemann
1,2
, Kathleen Draper
3
and
Claudia Kammann
4
1Ithaka Institute for Carbon Strategies, Arbaz, Valais, Switzerland
2Environmental Analytics, Agroscope, Zurich, Switzerland
3Ithaka Institute for Carbon Intelligence, Victor, NY, USA
4Department of Applied Ecology, Hochschule Geisenheim University, Geisenheim, Germany
ABSTRACT
Biochar, that is, carbonized biomass similar to charcoal, has been used in acute
medical treatment of animals for many centuries. Since 2010, livestock farmers
increasingly use biochar as a regular feed supplement to improve animal
health, increase nutrient intake efficiency and thus productivity. As biochar gets
enriched with nitrogen-rich organic compounds during the digestion process, the
excreted biochar-manure becomes a more valuable organic fertilizer causing lower
nutrient losses and greenhouse gas emissions during storage and soil application.
Scientists only recently started to investigate the mechanisms of biochar in the
different stages of animal digestion and thus most published results on biochar
feeding are based so far on empirical studies. This review summarizes the state of
knowledge up to the year 2019 by evaluating 112 relevant scientific publications on
the topic to derive initial insights, discuss potential mechanisms behind observations
and identify important knowledge gaps and future research needs. The literature
analysis shows that in most studies and for all investigated farm animal species,
positive effects on different parameters such as toxin adsorption, digestion, blood
values, feed efficiency, meat quality and/or greenhouse gas emissions could be found
when biochar was added to feed. A considerable number of studies provided
statistically non-significant results, though tendencies were mostly positive. Rare
negative effects were identified in regard to the immobilization of liposoluble feed
ingredients (e.g., vitamin E or Carotenoids) which may limit long-term biochar
feeding. We found that most of the studies did not systematically investigate biochar
properties (which may vastly differ) and dosage, which is a major drawback for
generalizing results. Our review demonstrates that the use of biochar as a feed
additive has the potential to improve animal health, feed efficiency and livestock
housing climate, to reduce nutrient losses and greenhouse gas emissions, and to
increase the soil organic matter content and thus soil fertility when eventually applied
to soil. In combination with other good practices, co-feeding of biochar may thus
have the potential to improve the sustainability of animal husbandry. However,
more systematic multi-disciplinary research is definitely needed to arrive at
generalizable recommendations.
Subjects Agricultural Science, Ecology, Soil Science, Veterinary Medicine, Environmental Impacts
Keywords Livestock emissions, Biochar feed, Mycotoxins, Animal health, Feed efficiency,
Pesticides, Animal digestion, Enteric methane emissions, Redox activity
How to cite this article Schmidt H-P, Hagemann N, Draper K, Kammann C. 2019. The use of biochar in animal feeding. PeerJ 7:e7373
DOI 10.7717/peerj.7373
Submitted 7May2019
Accepted 28 June 2019
Published 31 July 2019
Corresponding author
Hans-Peter Schmidt,
schmidt@ithaka-institut.org
Academic editor
Melanie Kah
Additional Information and
Declarations can be found on
page 37
DOI 10.7717/peerj.7373
Copyright
2019 Schmidt et al.
Distributed under
Creative Commons CC-BY 4.0
INTRODUCTION
Biochar is produced by pyrolysis from various types of biomass in a low-to-no oxygen
thermal process at temperatures ranging from 350 to 1,000 C(European Biochar
Foundation (EBC), 2012;International Biochar Initiative (IBI), 2015). Using water vapor or
CO
2
at temperatures above 850 C or chemical compounds like phosphoric acid and
potassium chloride, the biochar undergoes an activation process resulting in activated
biochar (i.e., activated carbon) (Hagemann et al., 2018). When produced from pure stem
wood, the solid phase of the pyrogenic process is known as charcoal. In contrast, the term
biochar indicates that a broad spectrumof biogenic materials can serve as feedstock. Biochar,
activated carbon and charcoal can all be considered as pyrogenic carbon materials.
The term biochar indicates that it is used for any purpose that does not involve its rapid
mineralization to CO
2
(e.g., burning it) (European Biochar Foundation (EBC), 2012). In a
broader sense, the term biochar denotes its intended long-time residence in the terrestrial
environment, either as a soil amendment or for other material-use purposes (Schmidt
et al., 2018). Since biochar-carbon decomposes much slower than the original biomass, the
application and use of biochar is considered as a terrestrial carbon sink on at least a
centennial scale (Zimmerman & Gao, 2013;Lehmann et al., 2015;Werner et al., 2018) and
is therefore a promising negative emission technology (IPCC, 2018).
During the first decade of modern biochar research summarized in Lehmann & Joseph
(2015), biochar was usually tested as a soil amendment that was applied pure to soils in
large quantities (>10 t/ha) revealing modest to large yield increases for a multitude of
crops in the tropics but only rarely in temperate climates (Jeffery et al., 2017). More
recently it was (re-)discovered that blending biochar with organic amendments such as
manure, cattle urine or compost may increase yields more significantly and in a broader
spectrum of climates and soils (Steiner et al., 2010;Kammann, Glaser & Schmidt, 2016;
Godlewska et al., 2017;Schmidt et al., 2017). As quality biochar is non-toxic and thus
even feedable and edible (European Biochar Foundation (EBC), 2012), this apparently
favorable combination of organic residues with biochar prompted researchers and a
rapidly increasing number of practitioners to conduct trials where biochar was not only
mixed with manure but also included as an input into animal farming systems. The
incremental addition of biochar to silage, feed, bedding material and liquid manure pit
demonstrated that biochar can be used in cascades. In addition to the direct benefits for
animal husbandry as discussed below in detail, biochar becomes thus enhanced with
organic nutrients which increases the economic viability of biochar application while
providing numerous environmental benefits along the (cascading) way.
When combined with silage, biochar can reduce mycotoxin formation, bind pesticides,
suppress butyric acid formation and enhance the quantity of lactic bacteria (Calvelo
Pereira et al., 2014). Farmers observed that when biochar was combined with straw or
saw dust bedding at 5–10% (vol) hoof diseases, odors and nutrient losses were reduced
(O’Toole et al., 2016). Moreover, farmers reported that adding 0.1% biochar (m/m) in
a liquid manure pit reduced odors, surface crust and nutrient losses (Schmidt, 2014;
Kammann et al., 2017). Throughout these cascades, the biochar becomes enriched with
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 2/54
organic nutrients and functional groups, while the cation exchange capacity and
redox activity increases, and pH decreases (Joseph et al., 2013). Analyses indicate
that, by enriching the biochar with liquids organic nutrients (whether in the digestive tract,
bedding, manure pit or by co-composting), the interior surfaces of the porous biochar
become drenched with an organic coating (Hagemann et al., 2017;Joseph et al., 2018).
This increases both water storage capacity and nutrient exchange capacity (Conte et al.,
2013;Kammann et al., 2015;Schmidt et al., 2015). The biochar becomes thus a more
efficient plant growth enhancing soil amendment, that improves the recycling of nutrients
from organic residues of animal farming (Kammann et al., 2015). The cascading use
of biochar in animal farming systems also reduces the environmentally harmful loss
of ammonia through volatilization or nitrate through leaching (Liu et al., 2018;Borchard
et al., 2019;Sha et al., 2019) and it has the potential to reduce greenhouse gas emissions
such as nitrous oxide (N
2
O) (Kammann et al., 2017;Borchard et al., 2019), or
methane (CH4) (Jeffery et al., 2016). To the best of our knowledge, no study so far has
quantified biochar emission reduction effects along a full cascade. The studies cited
above are reviews or meta-analyses summarizing mainly effects of the amendment of
biochar to soil.
Whenin2012thecascadinguseofbiocharandespecially its addition to animal feed began
in Germany and Switzerland (Gerlach & Schmidt, 2012), the biochar market in Europe started
to grow considerably. Since then, the largest proportion of industrially produced biochar
in Europe is sold for animal feed, bedding, manure treatment and thus subsequent soil
application (Kammann et al., 2017;O’Toole et al., 2016;Schmidt & Shackley, 2016). In 2016,
the European Biochar Foundation introduced a new biochar certification standard specifically
for animal feed (European Biochar Foundation (EBC), 2018) to allow for quality control,
as well as conformity with European regulations for animal feed.
When ingested orally, biochar has been shown to improve the nutrient intake efficacy,
adsorb toxins and to generally improve animal health (O’Toole et al., 2016;Toth &
Dou, 2016). After numerous veterinary papers published last century, a number of
scientific studies on biochar feeding have been published since 2010, dealing with biochars’
impact on the health of various animal species, on feed efficiency, pathogen infestation
and on greenhouse gas emissions. Thus, we review the current state of knowledge
regarding the use of biochar as a animal feed additive. We identify systematic gaps in the
scientific understanding as it is still mechanistically unclear why biochar, as a feed additive,
causes the observed effects. We also highlight potential side effects, the known and
potential effects on greenhouse gas emissions, the necessity for adapted regulatory practice
and quality control as well as the need for dedicated research to close knowledge gaps.
RESEARCH METHODS
This study predominantly selected research papers published between 1980 and 2019 but
included also a selection of historical articles and books published between 1905 and
1979. Some rare oral communications were included to reference and illustrate farmer and
feed certifier experiences.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 3/54
Search strategy
We searched the following electronic databases: Science Direct, Scopus, ISI Web of Science
and Research Gate. To identify the relevant publications, we used the following search
terms: (biochar OR charcoal OR activated carbon) and (animal OR feed OR livestock
OR livestock type (cow, poultry, sheep etc.) OR methane OR pesticides OR silage
OR manure). The references cited in the reviewed studies were also included in the search
and scanned separately for relevant publications. To summarize the historical literature
(20 studies) we used the Karlsruhe Virtual Catalogue and the literature cited in the
respective historical works in English, German and French. We further interviewed
Dr. Achim Gerlach, a veterinarian who has been treating large cattle herds with biochar for
nearly a decade; only a small fraction of his experiences are published in peer-reviewed
journals (Gerlach & Schmidt, 2012).
Selection of studies
The authors assessed the titles and abstracts of all retrieved references of relevance to the
objective of this review. Due to the relatively small number of studies, we included all
studies that investigated biochar or charcoal or activated carbon in vivo as feed additive for
improving performance and animal health (27 studies). We further selected in vivo or
in vitro studies when animal tissue or digestive liquids were used as medium and if they
were related to mycotoxin- (26 studies), bacteria related pathogen- (22 studies), poisoning
and drug overdoses (21 studies), and pesticide- (23 studies) adsorption or methane
emissions (12 studies). In total, 112 scientific studies on biochar effects in animal feeding
were reviewed. Reported results were only discussed as significant when p< 0.05 was
obtained in the respective study.
RESULTS AND DISCUSSION
Historical overview
The use of biochar/charcoal as feed or feed additive before 2010
Charcoal is one of the oldest remedies for digestive disorders, not only for humans but also
for livestock. Cato the Elder (234 -149 BC) was one of the first to mention it in his classic
On Agriculture:“If you have reason to fear sickness, give the oxen before they get sick
the following remedy: 3 grains of salt, 3 laurel leaves, [ :::], 3 pieces of charcoal, and 3 pints
of wine.”(Cato, 1935, §70). Besides the administration of medicinal herbs, oil or clay,
charcoal was widely used by traditional farmers all over the world for internal disorders of
any sort. Apparently, it never did any harm but was mostly beneficial (Derlet & Albertson,
1986). For some animals like chicken or pigs, the charcoal was administered pure; for
others it was mixed with butter (cows), with eggs (dogs) or with meat (cats).
A textbook on animal husbandry dating from 1906 observed: “Swine appear to have a
craving for what might be called ‘unnatural substances’. This is especially true of hogs
that are kept in confinement, which will eat greedily such substances as charcoal, ashes,
mortar, soft coal, rotten wood etc. It is probable that some of the substances are not good
for hogs, but there is no doubt that charcoal and wood ashes have a beneficial effect,
the former being greatly relished”(Day, 1906).
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 4/54
19th century and early 20th century agricultural journals printed many discussions on
the benefits of various “cow tonics,”mostly composed of charcoal and a variety of other
ingredients including spices, such as cayenne pepper, and digestive bitters like gentian.
Manufacturers of these tonics claimed they would reduce digestive disorders, increase
appetite and improve milk production (Pennsylvania State College, 1905).
At this time in the USA, charcoal was considered a superior feed additive for increasing
butterfat content of milk. Cow’s milk was tested for butterfat content in competitions
where top-producing cows could win a prize. Farmers took great care in formulating the
feed ration for such tests: The grain mixture fed during the test consisted of 100 pound
of distillers dried grains, 50 pounds of wheat bran, 100 pounds of ground oats, 100 pounds of
hominy, 100 pounds of cottonseed meal :::. Charcoal is seldom if ever left out the test ration
by many of the breeders”(Savage, 1917).
The use of activated and non-activated biochar feed for animal health was already
being researched and recommended by German veterinarians at the beginning of the last
century. Since 1915, research into activated biochar had revealed its effect in reducing
and adsorbing pathogenic clostridial toxins from Clostridium tetani and Clostridium
botulinum (Skutetzky & Starkenstein, 1914;Luder, 1947). Mangold (1936) presented a
comprehensive study on the effects of biochar in feeding animals, concluding that “the
prophylactic and therapeutic effect of charcoal against diarrheal symptoms attributable to
infections or to the type of feeding is known. In this sense, adding charcoal to the feed
of young animals would seem a good preventive measure.”Volkmann (1935) described an
effective reduction in excreted oocysts through adding biochar to the food of pets with
coccidiosis or coccidial infections.
Later, Totusek & Beeson (1953) wrote that biochar products are used since at least 1880
in US-American hog breading and since 1940 in feed for poultry. In their influential
article, the authors provided an extensive list of references. At around the same time,
Steinegger & Menzi (1955) wrote: “It is generally common in Switzerland to add biochar to
chick feed and to the meal for laying hens to prevent digestive problems and to achieve a
regulating effect on digestion.”
Biochar and wild animals
At first glance it might seem somewhat unnatural to feed biochar/charcoal to animals, but
in fact even wild mammals occasionally eat biochar if it is available to them. In nature,
charcoal residues from wild fires can still be found years later. Deer and elk are
reported to eat from charred trees in Yellowstone National Park and domestic dogs to
eat charcoal briquettes (Struhsaker, Cooney & Siex, 1997). The Zanzibar red colobus
(Procolobus kirkii), a small monkey regularly eats charcoal to help digest young Indian
Almond (Terminalia catappa) or mango (Mangifera indica) leaves that contain toxic
phenolic compounds (Cooney & Struhsaker, 1997). Struhsaker, Cooney & Siex (1997)
observed that individual colobus monkeys consumed about 0.25–2.5 g of charcoal per kg
body weight daily. Additional adsorption tests performed by Cooney & Struhsaker
(1997) indicated that in particular the African kiln charcoals (which the monkeys
also ate) were surprisingly good at adsorbing hot-water-extracted organics from the
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 5/54
above-mentioned tree leaves. Thus, the authors concluded that the monkeys’charcoal
consumption was likely a (self-)learned behavior, increasing the digestibility of their
typical leaf diet. Interestingly, a population count of colobus monkeys on this African
island showed that they reached the highest population density of all monkey species
worldwide. It seems, therefore, that the daily consumption of such wood-based biochar
has no negative long-term effect at least not on these monkeys.
Mechanisms of biochar in feed digestion
Adsorption
Before biochar was investigated and used as a regular feed additive for animals in the early
2010s, charcoal (i.e., biochar made from wood) and activated carbon (i.e., activated biochar
when made from biomass; Hagemann et al., 2018) was considered a veterinary drug
to tackle indigestion and poisoning. Charcoal was known for many centuries as an
emergency treatment for poisoning in animals (Decker & Corby, 1971). Biochar has been
and still is used because of its high adsorption capacity for a variety of different toxins
like mycotoxins, plant toxins, pesticides as well as toxic metabolites or pathogens.
Adsorption therapy, which uses activated biochar as a non-digestible sorbent, is considered
one of the most important ways of preventing harmful or fatal effects of orally ingested
toxins (McKenzie, 1991;McLennan & Amos, 1989).
From a toxicology perspective, most of the effects of biochar are based on one
or several of the following mechanisms: selective adsorption of some toxins like dioxins,
co-adsorption of toxin containing feed substances, adsorption followed by a chemical
reaction that destroys the toxin and desorption of earlier adsorbed substances in later
stages of digestion (Gerlach & Schmidt, 2012). However, classifiable distinctions need to
be made to the time-dependent and partly overlapping processes of adsorption,
biotransformation, desorption and excretion of the toxic substances throughout the
digestive system of animals.
Schirrmann (1984) described the effects of activated carbon on bacteria and their toxins
in the gastrointestinal tract as:
1. Adsorption of proteins, amines and amino-acids.
2. Adsorption of digestive tract enzymes, as well as adsorption of bacterial exoenzymes.
3. Binding, via chemotaxis, of mobile germs.
4. The selective colonization of biochar with gram-negative bacteria might result in
decreased endotoxin release as these toxins could be directly adsorbed by the colonized
biochar when gram-negative bacteria dying-off.
One further major advantage of the use of biochar is its “enteral dialysis”property,
that is, already adsorbed lipophilic and hydrophilic toxins can be removed from the blood
plasma by the biochar, as the adsorption power of the huge surface area of the biochar
interacts with the permeability properties of the intestine (Schirrmann, 1984).
Susan Pond (1986) explained various mechanisms by which biochar can eliminate
toxins from the body. First, biochar can interrupt the so-called enterohepatic circulation of
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 6/54
toxic substances between the intestine, liver and bile. It prevents compounds such as
estrogens and progestagens, digitoxin, organic mercury, arsenic compounds and
indomethacin from being taken up in bile. Second, compounds such as digoxin, which are
actively secreted into the intestine, can be adsorbed there. Third, compounds such as
pethidines can be adsorbed to the biochar, which passively diffuse into the intestine.
Fourth, the biochar can take up compounds that diffuse along a concentration gradient
between intestinal blood and primary urine.
Redox activity of biochar-based feed additives
Although the adsorption capacity is the most prominent function of biochar to explain its
positive impacts when fed to animals, adsorption alone cannot explain all phenomena
that are observed in biochar feeding experiments. Another pivotal, but still widely
overlooked function of biochar is its redox activity. Biochars act as so called geobatteries
and geoconductors that can accept, store and mediate electrons from and for biochemical
reactions (Sun et al., 2017). Low temperature biochars (HTT of 400–450 C) function
as geobatteries mainly due to their phenol and quinone surface groups. High temperature
biochars (HTT >600), on the other hand, are good electrical conductors (Mochidzuki
et al., 2003;Yu et al., 2015). Due to both of these qualities, both, high and low temperature
biochars, can act in biotic and abiotic redox-reactions as electron mediators (Van Der
Zee & Cervantes, 2009;Husson, 2012;Liu et al., 2012;Kappler et al., 2014;Kluepfel et al.,
2014;Joseph et al., 2015a;Yu et al., 2015;Sun et al., 2017). Biochar can accept and
donate electrons as, for example, in microbial fuel cells where activated biochar can be
used as an anode and as a cathode (Gregory, Bond & Lovley, 2004;Nevin et al., 2010;
Konsolakis et al., 2015). The electrical conductivity of biochar is, however, not based on
continuous electron flow, like in a copper wire, but on discontinuous electron hopping
(Kastening et al., 1997), which is of essential importance for biochar’s function as a
(microbial) electron mediator or so-called electron shuttle, facilitating even inter-species
electron transfer (Chen et al., 2015). Due to the comparably large size of biochar particles,
the electron transfer capacity of biochar’s carbon matrices may lead to a relatively
long-distance electron exchange that provides a spatially more extensive accessibility
to alternative electron acceptors such as minerals for anoxic microbial respiration
(Sun et al., 2017).
During the microbial decomposition of organic substances in the gastrointestinal tract
and particularly in the anaerobic rumen, digestive microbes require a terminal electron
acceptor to get rid of surplus electrons that accumulate during the degradation of organic
molecules. As electrons do not exist in a free state under ambient environmental
conditions and cannot be stored in large enough quantities by cells, organisms always
depend on the availability of both an electron donor (e.g., the metabolized organic matter)
and an acceptor to which surcharge electrons can be transferred. This usually occurs
in so-called redox reactions where molecules or atoms that donate an electron are coupled
through electro-chemical reactions with molecules or atoms that accept an electron.
To allow this electron transfer, these chemical or biochemical redox-reactions usually have
to take place in very close (molecular) proximity.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 7/54
The coupling of electron donating and electron accepting reactions can, however, be
bridged by so-called electron mediators or electron shuttles. Those electron meditators can
take up an electron from a chemical reacting molecule, solid interphase or microorganism
and provide it to another molecule, atom, solid interphase or microorganism. Well
known and investigated electron mediating compounds include thionine, tannins, methyl
blue or quinone, showing comparable capacities to humic substances and biochar
(Van Der Zee et al., 2003;Liu et al., 2012;Bhatta et al., 2012;Kluepfel et al., 2014).
A well-balanced animal feed regime should contain multiple electron mediating
substances. In the high-energetic diets used in intensive livestock farming, the supply with
electron-shuttling substances is, however, often insufficient (Sophal et al., 2013). When
inert or other non-toxic electron mediators like biochar or humic substances are added
to high-energy feed, several redox reactions may take place more efficiently, which could in
turn increase the feed intake efficiency (Liu et al., 2012;Leng, Inthapanya & Preston, 2013).
Biochar, specifically, can act as both a sole electron mediator or a synergistic electron
mediator that increases the efficiency of other mediators (Kappler et al., 2014).
Inside the gastro-intestinal tract, nearly all feed-degrading reactions are facilitated
by microorganisms (mostly bacteria, archaea and ciliates). Within those reactions,
bacterial cells may transfer electrons to biofilms or via biofilms to other terminal electron
acceptors (Richter et al., 2009;Kracke, Vassilev & Krömer, 2015). However, biofilms are
rather poor electric conductors and the electron-accepting capacity is low. Hence,
microbial redox reactions can be optimized by electron shuttles, such as humic acids or
activated biochar whose electrical conductivity is 100–1,000 times higher than that of
biofilms (Aeschbacher et al., 2011;Liu et al., 2012;Saquing, Yu & Chiu, 2016). Although the
conductivity of non-activated biochar is lower compared to activated biochar, it has
been shown that it can efficiently transfer electrons between bacterial cells (Chen et al.,
2015;Sun et al., 2017). Bacteria were shown to donate an electron to a biochar particle
while other bacteria of different species took up (accepted) an electron at another site of the
same biochar particle. The biochar acts here like a “battery”(or electron buffer) that
can be charged and discharged, depending on the need of biochemical (microbial)
reactions (Liu et al., 2012). Moreover, as biochar can be temporarily oxidized or reduced by
microbes (i.e., biochar is depleted or enriched in electrons), it can buffer situations with a
(temporary) lack of electron donors or terminal electron acceptors (redox buffering
effect) (Saquing, Yu & Chiu, 2016). A principal aim of feeding biochar to animals could
thus be to overcome metabolic redox limitations by enhancing electron exchange between
microbes, and between microbes and terminal electron acceptors.
The redox-active carbonaceous backbone of the biochar as well as minerals it contains,
such as iron (Fe(II) and/or Fe(III)) and manganese (Mn(III) or Mn(IV) minerals), can
electrically support microbial growth in at least four different ways: (1) as an electron
sink for heterotrophy-based respiration, (2) as an electron sources for autotrophic growth,
(3) by enabling cell-to-cell transfer of electrons and (4) as an electron storage material
(Shi et al., 2016). It can be hypothesized that enabling of extracellular electron transfer
contributes to a more energy efficient digestion resulting in higher feed efficiency when
activated or non-activated biochar is administered. Moreover, the electrochemical
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 8/54
effects need to be considered as a major factor for explaining possible shifts in the
functional diversity of the microbial community in the digestive system (Prasai et al.,
2016). Leng, Inthapanya & Preston (2012) also suggested that electron transfer between
biochar and microorganisms could be one of the reasons why feeding biochar to cows led
to reduced methane emissions in their studies (see chapter 6).
It is further very likely that biochar has the function of a redox wheel in the digestive
tract, comparable to Fe
III
–Fe
II
-redox wheels. It could act jointly as an electron acceptor
and donator coupling directly various biotic and abiotic redox-reactions comparable
to mixed valent iron minerals (Davidson, Chorover & Dail, 2003;Li et al., 2012;Joseph
et al., 2015a;Quin et al., 2015). Beside its polyaromatic backbone, biochar contain,
depending on the production process, a multitude of volatile organic carbons (VOC)
(Spokas et al., 2011). Some of the pyrolytic VOCs are strong electron acceptors and may
act, like a redox wheel similar to how quinone works (Van Der Zee et al., 2003). Some of
these pyrolytic VOCs that often undergo oxidative modifications during the aging of
biochar (Cheng & Lehmann, 2009) are so-called redox-active moieties (RAMs) that have
been shown to contribute to the biodegradation of certain contaminants (Yu et al., 2015).
It can be surmised that in the digestive tract, a multitude of RAMs, adsorbed on the
surfaces of biochar particles, can act as redox-wheels with various microorganisms. It can
be further hypothesized that when biochar buffers electrons in the vicinity of redox active
surface groups, it may provide stabile micro-habitats with different redox-pH-milieus
for different species of microorganisms (Yu et al., 2015). Moreover, biochar adsorbs certain
feed and metabolic substances like tannins, phenols or thionin, which are also electron
acceptors and which might further increase the electron buffering of biochar particles
during its passage through the digestive tract (Kracke, Vassilev & Krömer, 2015).
Biochar, wood vinegar (i.e., aqueous solutions of condensed pyrolytic gases) and humic
substances can act as redox buffering substances (Husson, 2012;Kluepfel et al., 2014)
which may explain why the feeding of biochar, pyrolytic vinegar and humic substances
often show similar effects; and why the blending of biochar with wood vinegar or
humic substances seems to reinforce the effects (Watarai, Tana & Koiwa, 2008;Gerlach
et al., 2014). However, unlike both dissolved organic substances, biochar provides a highly
porous framework with high specific surface area, where humic-like substances or
pyrolytic vinegar can be adsorbed and unfurl three-dimensionally as a coating of the
inner-porous aromatic carbon surfaces of biochar. Due to the redox buffering effect of
biochar blended with humic substances or wood vinegar, variations of the redox potential
may be minimized in the proximity of biochar particles, which could support those
species of microorganisms that find their optimum at these redox potentials (Kalachniuk
et al., 1978;Cord-Ruwisch, Seitz & Conrad, 1988). Biochar particles may thus provide
selective hotspots of microbial activity. It can be assumed that the buffering of the redox
potential as well as the effect of electron shuttling between microbial species can have
a selective, microbial milieu forming effect, which facilitates and accelerates the
formation of functional microbial consortia (Kalachniuk et al., 1978;Khodadad et al., 2011;
Sun et al., 2017).
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 9/54
The mechanistic understanding of biochar used as feed additive, especially with regard
to its impact on microbial mediated redox reactions, is clearly in its infancy (Gregory,
Bond & Lovley, 2004;Nevin et al., 2010;Konsolakis et al., 2015). However, we hypothesize
with some confidence that biochar has a direct electro-chemical influence on digestive
reactions, and that this is one, if not the main, reason for the extremely varying effects
of different biochars. Electrical conductivity, redox potential, electron buffering (poising)
and electron transfer capacity (shuttling) of a given biochar depend highly on the type
of pyrolyzed feedstock, pyrolytic conditions (Kluepfel et al., 2014;Yu et al., 2015) and
especially on pyrolysis temperature (Sun et al., 2017). The higher the temperature above
600 C, the better is the electron transfer rate and electrical conductivity (Sun et al., 2017).
However, the higher the VOC content of, for example, lower-temperature biochars
and higher abundance of surface functional groups on lower temperature biochars
(400–600 C), the more important the mediated electron transfer onto/from the biochar
may become (Joseph et al., 2015a;Yu et al., 2015;Sun et al., 2017). In addition, the mineral
content of biochars should be taken into account as well, since it does not only
influence biochar’s electro-chemical behavior, but it may also catalyze various biotic
and abiotic reactions (Kastner et al., 2012;Anca-Couce et al., 2014).
Specific toxin adsorption
Adsorption of mycotoxins
The contamination of animal feed with mycotoxins is a worldwide problem that affects up
to 25% of the world’s feed production (Mézes, Balogh & Tóth, 2010). Mycotoxins are
mainly derived from mold fungi, whose growth on fresh and stored animal feed is difficult
to prevent, especially in humid climates. Mycotoxin-contaminated feed can result in
serious diseases of farm animals. To protect the animals, adsorbents are usually added to
the feed to bind the mycotoxins before ingestion. In addition to the frequently used
aluminosilicates, activated carbon and special polymers are increasingly being used
(Huwig et al., 2001).
One of the most common mycotoxins is aflatoxin (Alshannaq & Yu, 2017), which
has, therefore, been used in numerous studies as a model substance to investigate the
adsorption behavior of biochar and how it reduces the uptake of the toxin in the digestive
tract and hence in the animal blood and in milk (Galvano et al., 1996a). Galvano et al.
(1996b) were able to reduce the extractable aflatoxin concentration in animal feed by up to
74% and the concentration in milk by up to 45%, by adding 2% activated biochar to
pelleted aflatoxin-spiked feed for dairy cows. The non-systematic comparison of different
activated biochars, however, showed that there are large differences in the adsorption
efficiency between different types of (activated) biochar.
Diaz et al. (2002) showed in an in vitro sorption batch study that four different activated
carbons adsorbed 99% of the aflatoxin B from a 0.5% aflatoxin B-spiked solution when
activated biochars were dosed at 1.11 g on 100 ml. However, when Diaz administered
0.25% activated carbon to aflatoxin-B contaminated feed for dairy cows a year later
(Diaz et al., 2004), they were unable to demonstrate any significant reduction in aflatoxin B
levels in the milk. Here, it has to be considered that in the in vivo test, an insufficiently
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 10/54
characterized (activated) biochar was fed at a low concentration of 0.25% of the feed fresh
weight, whereas in the in vitro studies, the biochar was added at 1% to the aqueous
solution, that is, four times higher, and in the absence of a feed matrix.
Galvano et al. (1996a) also investigated the adsorption capacity of 19 different
activated carbons for two mycotoxins, ochratoxin A and deoxynivalenol, and found that
the activated biochar adsorbed 0.80–99.86% of the ochratoxin A and up to 98.93% of the
deoxynivalenol, depending on the type of activated biochar. The large range of results
clearly confirms the importance of a systematic characterization and classification of
biochar properties. However, Galvano et al. concluded that neither the iodine number used
for activated biochar characterization, nor the Brunauer–Emmet–Teller specific surface
area derived from N
2
gas-adsorption isotherms allowed straightforward predictions of
the adsorption capacity for these mycotoxins.
Di Natale, Gallo & Nigro (2009) compared various natural and synthetic adsorbent feed
additives for dairy cows to reduce the aflatoxin content in milk. Activated biochar
showed the highest toxin reduction capacity (>90% aflatoxin reduction in milk with 0.5 g
aflatoxin per kg diet). Analytical studies of the milk quality also showed slight positive
effects on the milk composition with regard to organic acids, lactose, chlorides, protein
content and pH. The authors explained the high adsorption capacity with the high
specific surface area in combination with a favorable micropore size distribution of the
biochar, and the high affinity of aflatoxin for the polyaromatic surface of the biochar
in general (Di Natale, Gallo & Nigro, 2009).
Bueno et al. (2005) investigated the adsorption capacity of various doses of activated
biochar (0.1%, 0.25%, 0.5%, 1%) for zearalenone, a dangerous estrogenic metabolite of the
fungus species Fusarium, for which so far no treatment agents had been found. In vitro,
all zearalenone could be bound at each of the four biochar doses. However, in vivo,
where a wide variety of mycotoxins and numerous other organic molecules compete with
the free adsorption surfaces of biochar, hardly any specific adsorption could be achieved.
A study with Holstein dairy cows investigated to what extent the negative effects of
fungal-contaminated feed silage can be reduced by co-feeding activated biochar at 0, 20 or
40 g daily (Erickson, Whitehouse & Dunn, 2011). Cows fed the biochar amendment and
the contaminated silage had higher feed intake and improved digestibility of neutral
detergent fiber, hemicellulose and crude protein and had higher milk fat content compared
to the control without biochar. When the same daily amounts of biochar were
administered to uncontaminated quality silage, no changes in digestion behavior, milk
quality or any other effect on the dairy cows could be detected. However, the authors
showed in a second experiment that cows, when given the choice, clearly preferred good
quality silage to contaminated silage either with or without biochar. They concluded
that farmers should focus on providing high quality feed rather than mitigating negative
effects of contaminated silage with biochar.
While Piva et al. (2005) found no protection against the injurious effects of fumonisin,
a highly toxic mycotoxin, following a 1% addition of biochar to the feed of piglets,
Nageswara Rao & Chopra (2001) showed that the addition of biochar to aflatoxin B1
contaminated feed of goats reduced the transfer of the toxin (100 ppb) to the milk by 76%.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 11/54
In the latter trial, the efficiency of activated biochar was significantly higher than that of
bentonite (65.2%). Both adsorbents did not affect the composition of goat’s milk nor the
average level of milk production.
In vitro studies with porcine digestive fluids showed high rates of adsorption of
Fusarium toxins such as deoxynivalenol (67%), zeralenone (100%) and nivalenol (21%)
through activated biochar (Avantaggiato, Solfrizzo & Visconti, 2005;Döll et al., 2007).
On the other hand, Jarczyk, Bancewicz & Jedryczko (2008) found no significant effect when
they added 0.3% activated biochar to the diet of pigs. Neither in the blood serum nor
in the kidneys, the liver or in the muscle tissue could the ochratoxin concentrations be
reduced by this small amount of supplement with uncharacterized industrial biochar
(Jarczyk, Bancewicz & Jedryczko, 2008). However, no adverse effect was noted either.
Mycotoxins often cause serious liver damage in poultry. Biochar administered at daily
rates of 0.02% of the body weight significantly increased the activity of key liver enzymes
(Ademoyero & Dalvi, 1983;Dalvi & Ademoyero, 1984). While aflatoxin (10 ppm)
reduced feed intake and weight gain of broiler chickens, the addition of 0.1% biochar to
the feed (w/w) reversed the negative trend (Dalvi & McGowan, 1984).
Comparing the effect of activated biochar with a conventionally used alumina product
(hydrated sodium calcium aluminosilicate), it was found that the alumina product resulted
in considerable liver and blood levels of aflatoxin B when administered at 0, 40, 80 mg
AFB1 per kg diet, but not when combined with a 0.25% and 0.5% biochar treatment
(Kubena et al., 1990;Denli & Okan, 2007). In another study, activated biochar reduced the
concentration of aflatoxin B in the feces of chickens for fattening, but only if the biochar
was administered separately from the feed (Edrington et al., 1996). However, Kim et al.
(2017) showed with an in vivo pig feeding trial that the aflatoxin absorption capacity was
reduced by 100%, 10% and 20%, respectively, for three different biochars supplemented
at 0.5% to the same basal diet, again demonstrating the importance of considering
specific biochar properties. The importance of dosage was confirmed in another recent
poultry trial where 0.25% or 0.5% activated biochar was added to an aflatoxin B1
contaminated diet, decreasing aflatoxin B1 residues in the liver of the birds by 16–72%,
depending on the aflatoxin B1 and biochar dosages (Bhatti et al., 2018).
In their review article, Toth & Dou (2016) document further conflicting studies in which
biochar feeding may or may not mitigate the effects of mycotoxin intoxication. The results
of most studies on sorption in aqueous solution (in vitro) did not correlate with the
results in corresponding in vivo test results (Huwig et al., 2001). Thus, in vitro studies have
to be interpreted with care, because matrix effects can dramatically impact mycotoxin
sorption, for example, Jaynes, Zartman & Hudnall (2007) found that an activated carbon
(Norit, Boston, MA, USA) could sorb up to 200 g/kg aflatoxin, but only in clear solution.
In a corn meal suspension, sorption capacity was 100 times lower due to matrix effects.
Matrix effects in the digestive tract can be expected to be even more complex due to
varying pH and redox conditions. Still, based on our review, we conclude that negative
effects of certain mycotoxins such as deoxynivalenol (Devreese et al., 2012,2014;Usman
et al., 2015) and zearalenone (Avantaggiato, Havenaar & Visconti, 2004) can be effectively
suppressed with rather low dosages of activated biochar amended to feed, while no benefit
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 12/54
was found for aflatoxin. It can be hypothesized that (activated) biochar is only able to
suppress negative effects of mycotoxins that are rather hydrophobic (Avantaggiato,
Havenaar & Visconti, 2004).
However, most of these studies have in common that only commercial activated
carbons and biochars were used without proper characterization, that is, systematic trials
with biochar of different feedstock (e.g., wood vs. herbaceous feedstock) and production
conditions (e.g., temperature) are barely available. Thus, systematization of the results
remains difficult.
Adsorption of bacteriological pathogens and their metabolites
The use of activated and non-activated charcoals to improve animal health was
recommended and studied by German veterinarians as far back as the beginning of the 20th
century. In 1914, the adsorbing effect of charcoal for various toxins in the digestive tract
was described by Skutetzky & Starkenstein (1914). First experiments with bacterial toxins
of Clostridium tetani and Clostridium botulinum as well as with diphtheria toxin were
performed as early as 1919 (Jacoby, 1919). In particular, Wiechowski pointed out how
important the quality of the charcoal is, and how different the effect of different charcoals on
the toxin adsorption can be (Wiechowski, 1914). Ernst Mangold described in 1936 the effect
of charcoal in animal feeding comprehensively and concluded: “The prophylactic and
therapeutic effect of charcoal on infectious or feeding-related diarrhea is clear, and based on
this observation, the co-feeding of charcoal to juvenile animals appears as an appropriate
prevention”(Mangold, 1936). At about the same time, Albert Volkmann published his
findings about efficient reduction of oocyst excretion resulting from coccidiosis and coccidial
infections when charcoal was fed to domestic animals (Volkmann, 1935).
Gerlach et al. (2014) demonstrated that daily supplement of 400 g of a high-temperature
wood-based biochar (i.e., HTT 700 C) significantly reduced the concentration of antibodies
against the Botox-producing pathogen Clostridium botulinum in the blood of cattle
indicating the suppression of the pathogen. They concluded that the neurotoxin
concentration was reduced by the biochar in the gastrointestinal tract of the animals.
The feeding of only 200 g of biochar per day did not show the same efficiency. However,
when this lower dosage was mixed with 500 ml of lactobacilli-rich sauerkraut juice, a similar
significant reduction of Clostridium botulinum antibodies in the blood could be measured.
Knutson et al. (2006) fed sheep infected with Escherichia coli and Salmonella
typhimurium 77 g of activated biochar per animal per day. Although Naka et al. (2001) had
shown earlier by in vitro trials that E. coli O157: H7 (EHEC) cell counts were reduced
from 5.33 10
6
by five mg/ml activated biochar to below 800, the in vivo test by Knutson
et al. with the same activated biochar (DARCO-KB; Norit) revealed no biochar-related
binding of either E. coli or S. typhimurium in the gastrointestinal tract of sheep. The
authors hypothesized that either the biochar binding sites were occupied by competing
substances or other digestive bacteria or that the time between infection with the pathogen
and administration of the biochar was too long.
Schirrmann (1984) indicated that biochar has a particularly strong adsorption or
suppression capacity for gram-negative bacteria (e.g., E. coli) with high metabolic activity
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 13/54
(see more below in section “Administration of Biochar Feed and Biochar Quality Control”:
Side effects of biochar). Fecal E. coli counts in manure after feeding 0.25% activated biochar
or 0.50% coconut tree biochar were significantly lower than those of the control
without biochar in 10 days finishing pig trial, while the number of beneficial bacteria
Lactobacillus in feces increased in both biochar treatments (Kim et al., 2017).
Liquid cattle manure often contains E. coli O157: H7 (EHEC), which can contaminate
water and soil and enter the human food chain (Diez-Gonzalez et al., 1998). Biochar
can both adsorb E. coli and its toxic metabolites already in the digestive tract, as well as
reduce the spread of those bacteria in water and soil by adding it to manure. Gurtler et al.
(2014) investigated the effect of various biochar on the inactivation of E. coli O157:
H7 (EHEC) when applied to soils. All biochars produced by either fast or slow pyrolysis
from switchgrass, horse manure or hardwood significantly reduced EHEC concentrations,
with fast pyrolysis of barley and oak log feedstock providing the best results in the
contaminated soil mix, where EHEC after 4 weeks were untraceable using a cultivation
based assessment (Gurtler et al., 2014).
Abit et al. (2012) investigated how E. coli O157: H7 and Salmonella enterica spread in
water-saturated soil columns of fine sand or sandy loam, when the soil columns were
blended with 2% of different biochars. While chicken manure biochar prepared at 350 C
did not improve the binding of either bacteria, the addition of biochar prepared at 700 C
from pinewood or from chicken manure significantly reduced the spread of both
bacteria. In a later study, the authors showed significant differences in immobilization
between the two bacterial strains and suggested that the surface properties of the bacteria
played a significant role in the binding of these bacteria to the biochar (Abit et al., 2014).
The latter may turn out to be an important insight into biochar—bacterial interaction
and needs to be investigated systematically.
Since E. coli infections are likely to spread through cattle herds via water troughs, the
prophylactic addition of biochar to trough water may be a preventive measure that should
be further investigated.
In the study of Watarai & Tana (2005), the mixture of fodder with 1% and 1.5%
bamboo biochar and bamboo vinegar, respectively, slightly but significantly reduced the
levels of E. coli and Salmonella in chicken excrement. A patented biochar—wood vinegar
product, Nekka-Rich (Besnier, 2014), whose composition was not revealed, showed a
highly significant reduction of Salmonella in chicken droppings. It was further found that
the biochar—wood vinegar product reduced the pathogenic gram-negative Salmonella
enterica bacteria in the droppings, but not the intestinal flora of ubiquitous, non-toxic,
gram-positive Enterococcus faecium bacteria (Watarai & Tana, 2005).
A 0.3% bamboo biochar feed supplement (on DM base) suppressed the fecal
excretion of gram-negative coliform bacteria and gram-negative Salmonella in pigs up
to 20- and 1,100-fold, respectively, compared to controls without biochar (Choi
et al., 2009). The effect of biochar on the suppression of both bacterial species was of
the same order of magnitude as that of antibiotics. Feeding biochar resulted in a
190-fold increase in the number of beneficial intestinal bacteria and a 48-fold
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 14/54
higher level of gram-positive Lactobacilli compared to the treatment with antibiotics
(Choi et al., 2009).
In vitro studies revealed that biochar, as well as clay, can efficiently immobilize cattle
rotavirus and coronaviruses at rates of 79–99.99% (Clark et al., 1998). Since the diameter of
the viral particles were larger than the pore diameters of the clay and most pores of the
biochar, the authors suspected that binding was mainly due to the viral surface proteins
binding to the biochar.
In vitro and in vivo experiments with bovine calves showed that biochar, especially in
combination with wood vinegar, was able to control parasitic protozoan Cryptosporidium
parvum infection and to stop diarrhea of calves within one day. The number of oocysts
in the feces dropped significantly after a single day of feeding biochar; after 5 days no more
oocysts could be found in the feces of the calves (Watarai, Tana & Koiwa, 2008).
Similar results were reported when a commercial biochar wood acetic acid product
(Obionekk, Obione, Charentay, France) was tested as feed additive in young goats
(Paraud et al., 2011). The mixture administered twice or thrice daily reduced the clinical
signs of diarrhea already on the first day, and the oocyst shedding in the feces decreased
significantly. Over the period of the study, the mortality of the young goats was 20%
in the control group and only 6.7% in the treatment group that received Obionekkthree
times per day. Biochar feeding in goats may also reduce the incidence of parasites such as
cestode tapeworms and coccidia oocysts (Van, Mui & Ledin, 2006).
Adsorption of drugs
Numerous human medical studies on the use of activated carbon in poisoning have been
published in the 1980s providing important insights into the use of (activated) biochar as
feed especially to treat feed poisoning (Erb, Gairin & Leroux, 1989). The adsorbing effect of
activated carbon can be used to prevent the gastrointestinal uptake of most drugs and
numerous toxins (Neuvonen & Olkkola, 1988), which is typically more effective than
pumping out stomach contents. The repeated intake of activated carbon or biochar
improved the elimination of overdosed toxicologically effective substances such as aspirin,
carbamazepine, dapsone, dextropropoxyphene, cardiac glycosides and many more as
summarized by Neuvonen & Olkkola (1988). Moreover, a faster elimination of many
industrial and environmental toxins was assessed. In acute poisoning, 50–100 g of
activated biochar are administered to adults and about one g/kg of body weight to children.
The same authors also point out that there are no known serious side effects from
accidental ingestion. In the case of acute poisoning, Finnish physicians recommend
repeated oral treatment with activated carbon to reduce the risk of toxins being desorbed
from the biochar-toxin complex in the digestive cycle (Olkkola & Neuvonen, 1989).
In general, repeated oral administration of biochar increases the efficacy of detoxication
(Crome et al., 1977;Dawling, Crome & Braithwaite, 1978). However, regular
administration of 0.2% activated biochar in broiler feed did not significantly impact the
blood levels of the antimicrobial drugs doxycycline and tylosin, and of the coccidiostats
diclazuril and salinomycin. The pharmaceutical products were co-applied to the activated
carbon amended feed (De Mil et al., 2017).
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 15/54
Adsorption of pesticides and environmental toxins
Based on the excellent adsorption properties of biochar in relation to numerous pesticides,
insecticides and herbicides (Safaei Khorram et al., 2016;Mandal, Singh & Purakayastha,
2017;Cederlund, Börjesson & Stenström, 2017), which are increasingly found in animal
feed (Shehata et al., 2012), biochar is considered as animal feed additive. Of particular
importance is the adsorption of glyphosate, an herbicide that currently contaminates most
of the feed produced from genetically modified maize, rapeseed and soybean. Although
crop desiccation herbicides have been banned in Germany since May 2014, they are
still permitted in many other countries as a treatment shortly before grain harvest.
In addition to immobilizing magnesium and zinc, glyphosate has a potent antibiotic
activity (US Patent 7,771,736, EP0001017636, issued in 2010) and is suspected of causing
or promoting chronic botulism (Shehata et al., 2012). Glyphosate sorption efficiency
onto biochar particles is both dependent on pH (high sorption at low pH; Herath et al.,
2016) and the highest treatment temperature during biochar production (high sorption on
high-temperature biochars; Hall et al., 2018). However, Hall et al. (2018) showed that
glyphosate sorbed by biochar from pure water could be remobilized by adding 0.1M
monopotassium phosphate solution. This finding indicates that biochar-sorbed glyphosate
from feed may be remobilized in the digestive tract due to numerous ions potentially
competing for sorption sites. Further research in vivo and/or in vitro in relevant matrixes is
necessary, as low pH, for example, in the stomach, could favor glyphosate sorption (Herath
et al., 2016). In a study with 380 dairy cows, Gerlach et al. (2014) showed that daily feeding
with humic acids (120 g/day) or with a combination of 200 g of biochar and 500 g of
sauerkraut juice for 4 weeks significantly reduced the glyphosate concentration in the urine
of the cows that were fed with glyphosate contaminated silage.
Preliminary pesticide adsorption studies using biochar were already carried out in
the 1970s (Humphreys & Ironside, 1980). Deposits of the systemic organophosphorus
insecticide Runnel in the gastric mucosa of sheep were significantly reduced by the feeding
50 g of activated biochar per kg of feed, i.e., 5% amendment rate (Smalley, Crookshank &
Radeleff, 1971). While it was reported that activated biochar was successfully used to
adsorb pesticides in the digestive tracts of cattle, sheep and goats and were eventually
excreted (Wilson & Cook, 1970), similar experiments in chickens did not show any
significant effects on the residue levels in eggs and tissues (Foster et al., 1972). Feeding of
biochar with Dieldrin contaminated feed, an organochloride insecticide that was widely
used until the 1970s and is still persistent in the environment though it is banned
now, resulted in a very significant reduction of the Dieldrin concentration in the fat of the
pigs (Dobson et al., 1971). On the other hand, Fries et al. (1970) found no reduction in
the levels of Dieldrin and DDT in milkfat when cows were fed one kg of activated biochar
per day for 14 days. However, Wilson et al. (1971) found that when Dieldrin and
DDT-contaminated feed was mixed with activated biochar at 900 g per animal and day,
Dieldrin intake was reduced by 43% and DDT intake by 24%. When the contaminated
feed and biochar were administered separately, DDT intake was not reduced as both
the Dieldrin and DDT were probably absorbed by the oral mucosa already and not only in
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 16/54
the digestive tract (Fries et al., 1970). Activated biochar also showed very good in vitro
adsorption properties for the herbicide Paraquat (Okonek et al., 1982;Gaudreault,
Friedman & Lovejoy, 1985), which has been banned in the EU since 2007 but is still legal in
the US and other countries.
Fat-soluble organochlorine compounds such as Dibenzo-p-dioxin (PCDDs),
Dibenzofuran (PCDFs) and dioxin-like PCBs are ubiquitous environmental toxins, and
can often be detected in animal feed. These compounds accumulate in the adipose (fatty)
tissue of animals and humans. Experiments with activated biochar to adsorb these
substances were undertaken repeatedly in Japan (Yoshimura et al., 1986;Takenaka, Morita
& Takahashi, 1991;Takekoshi et al., 2005;Kamimura et al., 2009). All experiments
showed the strong affinity of the organochlorine compounds to activated biochar (Iwakiri,
Asano & Honda, 2007). Fujita et al. (2012) carried out an extensive experiment with
24 laying hens whose feed contained the organochlorine compounds mentioned above
and fed either with or without 0.5% biochar over a period of 30 weeks. Depending on
the structure and aromaticity of the organochlorine compounds, concentrations of
PCDDs/PCDFs, non-ortho PCBs and mono-ortho PCBs in the tissue and eggs of the
laying hens could be reduced by more than 90%, 80% and 50%, respectively (Fujita et al.,
2012). The fact that different organochlorine compounds are bound to different degrees
by biochar has been previously demonstrated in studies of contaminated fish oil
(Kawashima et al., 2009). In general, molecules with higher aromaticity have a stronger
affinity to biochar; this also applies to polycyclic aromatic hydrocarbons (Bucheli, Hilber &
Schmidt, 2015). Olkkola & Neuvonen (1989) concluded that the regular intake of
biochar as food supplement can be very helpful in the elimination of industrial and
environmental toxins including dioxins and PCB ingested by humans, a valid statement
for animal feed too.
Detoxification of plant toxins
Another benefit of a regular use of biochar is the alleviation of adverse effects of naturally
occurring though potentially harmful ingredients such as tannins contained in many
feeds (Struhsaker, Cooney & Siex, 1997). Tannins are complex and extraordinarily diverse
compounds that are partly beneficial but may also be harmful especially to ruminants.
Tannins are often found in high protein feeds such as legumes and the strong taste repels
the animals, which reduces digestability and weight gain (Naumann et al., 2013). Several
studies have investigated how biochar feeding alters the impact of tannin-rich foods. Van,
Mui & Ledin (2006) found that in goats, feeding 50–100 g of bamboo biochar per kg of a
tannin-rich acacia leaf diet increased daily weight gain by 17% compared to the control
without biochar. The authors found that digestion of crude proteins and nitrogen
conversion were significantly improved. Apparently, there was an optimal biochar dose:
While 50 and 100 g of bamboo biochar feed additions resulted in similar goat weight gains,
feeding 150 g of the same biochar per kg diet did not show any improvement compared
to control. Struhsaker, Cooney & Siex (1997) found, as previously described, that the
consumption of wild fire derived charcoal by Zanzibar red colobus monkeys increased the
nutritional efficiency of tannin-rich Indian almond and mango leaves. Banner et al. (2000)
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 17/54
found that the mixture of 10–25 g of activated biochar per day with rye significantly
increased the uptake of tannin and terpene rich compounds. Similar results for sage and
other terpenic and tannin-rich shrubs were reported by Rogosic et al. (2006,2009),
whereas others could not confirm that lambs consumed significantly more sage due to
biochar amended feed (Villalba, Provenza & Banner, 2002).
In winter, when hardly any fresh pasture plants are available, sheep also eat bitterweed
(Hymenoxys odorata DC.), which contains toxic levels of sesquiterpene lactones.
Poage et al. (2006) conducted therefore a series of bitterweed feeding trials with 0.5–1.5 g
of biochar per lamb per day mixed directly to the feed. While the lambs rejected the
bitterweed-containing feed without biochar, they did consume bitterweed up to 26.4%
of the total feed intake when combined with biochar revealing no signs of toxicosis.
Several studies have shown that poisoning of both livestock and sheep through
contamination of feed with Lantana camara, a species of flowering invasive species, can be
effectively treated with five g of biochar per kg of body weight (Pass & Stewart, 1984;
McLennan & Amos, 1989). While five out of six calves recovered from Lantana camara
poisoning after treatment with activated biochar, five out of six calves not treated
with biochar died (McKenzie, 1991). Treatment with bentonite achieved similarly high
cure rates, but complete healing took about twice as long. Similarly, significant results are
found for treating Yellow tulip (Moraea pallida) poisoning of cattle (Snyman et al., 2009)
and oleander poisoning of sheep (Tiwary, Poppenga & Puschner, 2009;Ozmaie, 2011).
Regular biochar feeding to improve performance and animal welfare
While therapeutic administration of biochar is a historically proven practice and has
been scientifically studied for over 50 years and recommended as a cure for numerous
symptoms, regular co-feeding of biochar with the purpose of improving productivity is
discussed again only since 2010. The feeding of livestock with biochar and biochar
products is rapidly spreading in practice, due to the apparently good experiences of
farmers, especially in Germany, Switzerland, Austria and Australia. However, systematic
scientific research on regular feeding with various types of biochar is still rare. One reason
for this is the fact that with veterinary medicine and biochar research two areas of
expertise collide that could hardly be more different and whose methods and vocabulary
have little in common. The latter also explains why usually non-characterized or only
poorly characterized biochar was used for feeding experiments.
Despite the diversity of biochar properties, key features of this heterogeneous material
are similar and apparently lead to comparable effects when provided as feed supplement.
The review of 27 peer reviewed scientific publications and clinical studies (Table 1)
about regular biochar feeding revealed no negative effects on animal welfare and
performance. Still, there are open question on some effects on long-term biochar feeding
that should be addressed prior to an unconfined recommendation of regular biochar
feeding. These include effects on the resorption of liposoluble feed ingredients and
potential interaction with the mycotoxin fumonisin. These risks of regular biochar feeding
are summarized in a separate section below. While results of feeding trials were sometimes
neutral (no significant difference between biochar and control treatment), often one or
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 18/54
Table 1 Overview of published studies on biochar feeding.
Animal Daily BC
intake
Feedstock HTT in C Activation Blend Weight
increase in %
Duration
in days
Other results and
remarks
Source
Cattle 0.6% of feed
DM
Rice hull 700 No 25 98 Reduced enteric
methane emissions
Leng, Inthapanya &
Preston (2013)
Bull 2% of feed
DM
Wood >600 No Vitamin A n.s. Kim & Kim (2005)
Cattle 1% of feed
DM
Rice husk >600 No 15 56 15% feed conversion
rate increase
Phongphanith &
Preston (2018)
Goat 1% of body
weight
Bamboo No 20 84 DM, OM, CP
digestibility and N
retention increased
Van, Mui & Ledin
(2006)
Goat 1% of feed
DM
No 27 90 DM, OM, CP
digestibility and N
retention increased
Silivong & Preston
(2016)
Pig 0.3% of feed
DM
Bamboo >600 Yes (900) Bamboo vinegar 17.5 42 Improved the quality
of marketable meat
Chu et al. (2013c)
Pig 0.3% of feed
DM
Wood No Stevia 11 Higher meat quality
and storage capacity
Choi et al. (2012)
Pig 1%, 3% and
5% of feed
DM
Wood 450 C No 25% wood vinegar n.s. 30 Increased duodenal
villus height
Mekbungwan,
Yamauchi &
Sakaida (2004)
Pig 1% of DM
feed
Wood >600 No Lactofermented n.s. 28 Kupper et al. (2015)
Pig 1% of DM
feed
>500 20.1 90 20.6% increased feed
conversion rate
Sivilai et al. (2018)
Poultry 0.2% of DM
feed
Wood No 17 49 Kana et al. (2010)
Poultry 0.2% of DM
feed
Maize cob No 6 49 Improved carcass
traits
Kana et al. (2010)
Poultry 2%, 4%, 8%
of feed DM
Citrus wood No 0 42 Heavier abdomen fat Bakr (2007)
Poultry 2.5%, 5%,
10% of feed
DM
Wood No 0 42 Weight increase up to
28 days but not
after 49 days
Kutlu, Ünsal &
Görgülü (2001)
Poultry 0.3% of feed
DM
Wood No 3.9 140 Reduced mortality by
4%
Majewska, Pyrek &
Faruga (2002),
Majewska, Mikulski
& Siwik (2009)
Duck 1% of DM
feed
Bamboo >650 No Bamboo vinegar n.s. 49 Intestinal villus
height increased
Ruttanavut et al.
(2009)
(Continued)
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 19/54
Table 1 (continued ).
Animal Daily BC
intake
Feedstock HTT in C Activation Blend Weight
increase in %
Duration
in days
Other results and
remarks
Source
Duck 1% of DM
feed
Wood No Kelp n.s. 21 Feed conversion rate
increased
Islam et al. (2014)
Poultry 4% of DM
feed
Woody
green waste
550 No n.s. 161 Egg weight increased
by 5%; feed
conversion ratio by
12%
Prasai et al. (2016)
Poultry 1% of DM
feed
Rice husk >550 No n.s. Reduced pathogenes
in feces
Hien et al. (2018)
Poultry 0.7% of DM
feed
Wood >650 No Lactofermented n.s. 36 Kupper et al. (2015)
Poultry 1% of DM
feed
Wood >650 No Lactofermented 5 37 Reduced foot pat and
hook lesions by 92%
and 74%
Albiker & Zweifel
(2019)
Flounder 0.5% of DM
feed
Bamboo No 18 50 Feed and protein
conversion rate
increased
Thu et al. (2010)
Flounder 1.5% of DM
feed
Wood No 20% wood vinegar 11 56 Highest feed
efficiency increase
of 10% at 0.5% BC
Yoo, Ji & Jeong (2007)
Stripfish 1% of DM
feed
Rice husk >600 No 36 90 Significantly
improved water
quality
Lan, Preston & Leng
(2018)
Stripfish 1% of DM
feed
Wood No 44 90 Significantly
improved water
quality
Lan, Preston & Leng
(2018)
Carp 0.5%, 1%,
2%, 4% of
DM feed
Bamboo No n.s. 63 Improved serum
indicators
Mabe et al. (2018)
Stripfish 2% of feed
DM
Bamboo No High VOC biochar 27 50 Survival rate increase
by 9%
Quaiyum et al. (2014)
Mean 9.9
Note:
The table indicates the percentage weight increase of various livestock depending on the ingested biochar type and daily feed intake. A total of 61% of the 28 data set delivered weight increases while the
remaining trials did not result in significant increases.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 20/54
several of the following effects were observed when biochar was provided as feeding
additive to livestock:
- Increase in feed intake
- Weight gain
- Increased feed efficiency
- Higher egg production and quality in poultry
- Strengthening of the immune system
- Improvement of meat quality
- Improvement of stable hygiene and odor pollution
- Reduction of claw and feet diseases
- Reduction of veterinary costs
Sorted by animal species, the following subsection reviews the scientific literature on
medium to long term feeding of biochar in regard to improving livestock productivity,
product quality, animal fitness, welfare and performance in the respective animal
farming system. Risks of regular biochar feeding are summarized in a separate section.
Cattle
As evidenced by farmer practice, veterinary advice, and European regulations, biochar
is already widely used as a regular feed supplement in cattle farming especially in
Germany, Austria and Switzerland (European Biochar Certification body, Hans-Peter
Schmidt, 2018, personal communication). However, there are only very few scientific
studies on biochar feed additives for cattle so far.
Since 2011, the German veterinarian Achim Gerlach has been feeding 100–400 g of high
temperature wood biochar (HTT 700 C) per cow per day to numerous herds of cattle
without detecting negative side effects (Gerlach & Schmidt, 2012; Hans-Peter Schmidt,
2018, personal communication). His survey of 21 farmers with at least 150 cattle revealed
that overall health and vitality had improved since they had started biochar feeding.
The somatic cell count (SCC) of the milk, an indicator of level of harmful bacteria,
decreased significantly, whereas milk protein and milk fat content increased. When
biochar additions to feed stopped, SCC quickly increased and a general loss of performance
of the animals compared to the biochar-feeding period was observed. It was also reported
that hoof problems were reduced, and that postpartum health was stabilized through
biochar co-feeding. Within 1–2 days after the onset of the biochar feeding, diarrhea
symptoms decreased and feces became firmer. Mortality rates declined, as did overall
veterinary costs. The liquid manure viscosity improved significantly and the odor load of
the manure decreased (Gerlach & Schmidt, 2012).
For 98 days, Leng, Preston & Inthapanya fed four cattle 0.6% of a rice hull-derived
biochar, with another four in a control group without biochar in their feed. The
biochar feeding resulted in a 25% higher weight gain compared to the control animals
(Leng, Preston & Inthapanya, 2013). Another study, however, did not find any significant
effect on weight gain and blood values in Hanwoo bulls when an undefined biochar
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 21/54
was administered at a rather high dose of 2% (Kim & Kim, 2005). A supplement of 1% rice
husk biochar was added to a basal diet consisting of ensiled cassava root, urea, rice straw
and fresh cassava foliage (Phongphanith & Preston, 2018). Live weight gain increased
by 15% and feed conversion rate also improved by 15% in the biochar treatment, compared
to the control without biochar supplement. Interestingly, when a rice wine distillers’
byproduct was added at 4% to the biochar-supplemented feed, the live weight gain and the
feed conversion rate increased by 60% compared to the control without either supplement.
They further found an increase of 18% compared to feeding with the rice wine
distillers alone (without biochar), or 31% compared to the biochar-only supplement.
This shows a strong interactive effect between the two supplements indicating that the
combination and interaction of biochar with other feed additives should increasingly be
investigated.
In a semi-continuous artificial rumen system, a high temperature biochar (HTT 600 C)
was added at 0%, 0.5%, 1% and 2% to a high-forage diet for 17 days. The biochar
linearly increased the digestion of dry matter, organic matter, crude protein and fiber.
Microbial protein synthesis also increased linearly. The microbial production of acetate,
propionate and total volatile fatty acids in the artificial rumen increased (Saleem et al., 2018).
As early as 2010, Marc McHenry pointed to the possibility of using biochar as a
feed additive not only to increase feed efficiency but to also increase nutrient availability of
the manure, to protect ground and surface water, and to sequester carbon in the soil
(McHenry, 2010). This cascading approach of improving not only animal performance and
welfare but also various ecosystem services has been the subject of discussion and
investigation by various authors since (O’Toole et al., 2016;Schmidt & Shackley, 2016;
Kammann et al., 2017). A far-reaching study of these cascades has been carried out by
Joseph et al. (2015b) in Australia: Since 2011, 60 grazing cattle on an Australian farm
were fed 330 g per day of a high temperature biochar (HTT 600 C) made from Jarrah
wood mixed with 100 g of molasses. From 2011 to 2015, soil organic matter, pH (CaCl
2
),
Colwell-P, Colwell-K, electrical conductivity and the content of all exchangeable
cations increased in the pasture soil that received the dung of the free ranging cattle.
During its passage through the digestion system of the cattle, biochar seems to capture
organic and mineral compounds with high plant fertilizing properties that would
otherwise probably be subject to rather quick leaching during storage. Most of these
captured plant nutrients (especially nitrogen and phosphorus) remain bound in the porous
structure of the biochar until its incorporation into the soil, where they likely become,
to a large extent, plant available as has also been found for biochar after aerobic
composting (Kammann et al., 2015;Schmidt et al., 2017). The authors of the Australian
study reported that increased retention of the digested nutrients in the biochar increased
the fertilizing effect of the bovine manure so that no additional fertilizers was required
for the pasture growth (Joseph et al., 2015b). However, they did not set-up a control pasture
to proof the latter. To prove their conclusion, a more systematic scientific experiment
would be required.
In addition to the improvement of the fertilizing properties of biochar-amended
manure, the application of biochar to manure either via feed or via bedding materials is
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 22/54
recommended as a potent strategy to reduce manure related greenhouse gas emissions
(Kammann et al., 2017). When biochar (wood shavings, HTT 650 C) was applied
at 13% to a cattle slurry and subsequently applied to a field at 3.96 m
3
biochar ha
-1
,
the biochar decreased total NH
3
-emissions by 77%, N
2
O-emissions by 63% and
CH
4
-emissions by 100% compared to the control of cattle slurry only (Brennan et al., 2015).
Since 2012, German and Swiss farmers have been using biochar in the production
of feed silage to stabilize lactic acid fermentation, prevent fermentation failure and
reduce risks of fungal infestation and formation of mycotoxins (O’Toole et al., 2016).
Lower levels of acetic acid and especially butyric acid are expected to minimize the risk of
Clostridia infestation. The high-water holding capacity of biochar appears to buffer the
water content of the silage, reducing the formation of excess fermentation liquids.
Calvelo Pereira et al. (2014) investigated the addition of various amounts and types of
biochar (0–2.1–4.2–8.1–18.6% made from pine wood or maize straw and pyrolyzed at
350, and 550 C, respectively) to hay silage and to cattle rumen liquid. The biochar
treatments did not significantly affect the investigated silage quality parameters, nor did it
negatively affect in vitro incubation with rumen fluid.
Goats and sheep
In a 12-week experiment with 42 young goats, it was found that feeding one g of bamboo
biochar per kg of bodyweight resulted in significantly higher crude protein intake (Van,
Mui & Ledin, 2006). The total amount of digested nitrogen increased and was thus lower in
the urine and feces of the animals. The body weight increased on average 53 g per day
compared to 44 g in the control group fed without biochar; a statistically significant
difference of 20%. The basic feeding of the goats included a large proportion of tannin-rich
acacia (Acacia mangium) leaves, and the authors hypothesized that biochar eased digestion
of those leaves by sorption of their tannins which apparently lead to higher crude
protein and improve total DM intake.
In a trial with groups of 12 goats (N= 3), growth performance was tested when a basal
diet of tannin rich leaves of Bauhinia acuminata were provided either with or without
1% biochar (Silivong & Preston, 2016). Biochar improved the nutrient assimilation and led
to a 27% increase in daily weight gain over the 100-day period of the trial. In another
study, a goat feed additive of 1.5% and 3% activated coconut biochar did not produce
significant improvement of feed intake nor did it alter the microbial community
structure compared with the control (Al-Kindi et al., 2017). However, the activated biochar
increased the fecal concentration of slowly decomposable carbohydrates while reducing
fecal N. This left the authors to surmise a beneficial slow-down in the mineralization
rate of the organic carbon contained in the manure when applied to soil, which may be
beneficial for the built-up of soil organic matter.
Horses
Very few publications exist yet on feeding biochar to horses. Edmunds et al. (2016)
investigated the effect of a woody biochar on the microbial community of the equine
hindgut and the metabolites they produce. They did not find any significant effect of the
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 23/54
biochar and concluded that the effect of biochar as a control for toxic substances is at its
highest in the foregut or midgut of animals, and therefore should have little impact on
the hindgut.
According to the EBC certified manufacturers of biochar and biochar products,
horse breeders and farmers widely apply biochar in horse manure management and also in
feeding, but apart from the above, not a single scientific study is known to the authors.
Pigs
Chu et al. published several fundamental studies in 2013 on the feeding of bamboo biochar
to pigs. Young pigs (N= 12) were fed for 42 days in addition to their normal fattening
diet (corn, wheat, soybean meal) either with 0%, 0.3% or 0.6% of biochar. The average
weight gain during the trial period was 750 g per day in the control without biochar
and 877 g per day in the 0.3% biochar treatment; this corresponded to a significant feed
efficiency increase of 17.5%. Doubling the biochar supplement to 0.6% did not lead to
statistically significant differences compared to the 0.3% treatment. While leucocytes,
erythrocytes, hemoglobin, hematocrit and platelets did not differ significantly between
the experimental groups, the biochar group showed significant positive effects on total
protein, albumin, cholesterol, HDL-CH and LDL-cholesterol levels in the blood plasma.
In addition, the cortisol content was significantly lower, which indicates a reduced
susceptibility to stress (Chu et al., 2013c). In another study, the authors showed that
feeding 0.3% and 0.6% bamboo biochar improved the quality of marketable meat and
the composition of pig fat, with an increase in unsaturated fatty acid content and a
decrease in saturated fat (Chu et al., 2013b). In a third study, the authors examined to
what extent biochar feeding can replace the regular supplementation of growth-promoting
antibiotics, something which is still legal in many though not all countries. In a very
comprehensive publication (Chu et al., 2013a), they concluded that feeding 0.3% bamboo
biochar gave the same growth rate in fattening pigs as the standard antibiotic treatment,
notably without the negative side effects to the environment that antibiotics can have.
Another hog feed trial was done in South Korea using different concentrations of
biochar and stevia mixed into the common diet of 420 pigs (Choi et al., 2012).
While neither 30 g of biochar nor 30 g of stevia per kg of feed alone had any significant
effects, 30 g of biochar plus 30 g of stevia had higher daily weight gain, feed efficiency
and immune responses as well as significantly higher meat quality and storage capacity of
meat products (Lee et al., 2011;Choi et al., 2012). In a Japanese study by Mekbungwan,
Yamauchi & Sakaida (2004), piglets were fed with increasing concentrations of a
4:1 mixture of a low temperature biochar (HTT 450) and wood vinegar. When fed with
1%, 3% and 5% of this mixture, no statistically significant effects on body weight and feed
efficiency were observed compared to the 0% control. However, duodenal villi height,
an animal health indicator, increased significantly. The same authors showed 4 years later,
with the same biochar-wood vinegar mix added at 1% and 3% to a protein-rich feed,
that the biochar treatments prevented negative side-effects of pig fattening with
protein-rich pigeon peas (Mekbungwan et al., 2008). The biochar-fed animals presented
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 24/54
significantly better values in parameters related to health such as intestinal villi height,
cell area and cell mitosis number compared to the control groups.
In Switzerland, Kupper et al. (2015) fed 80 weaned piglets for 28 days with a 1%
commercial biochar feed additive mixture that had undergone a lactic fermentation
beforehand. The biochar treatment did not reveal any significant difference in daily weight
gain, feed consumption and feed conversion rate compared to the control group that
received the same feed but without the biochar containing supplement. Moreover, no
significant difference in NH
3
-emissions of the stored or field applied manure was observed.
In a trial with native Moo Lath pigs (N= 20), the addition of 1% biochar to a basal
diet consisting of ensiled banana pseudo stem and ensiled taro foliage increased the feed
conversion rate by 10.6% compared to the control. The total weight gain of the piglets
was on average higher by 20.1% (p= 0.089) after the 90 days of the experiment
(Sivilai et al., 2018).
Poultry
Of all publications on the performance-enhancing use of biochar, a majority have focused
on its use with poultry, not least because scientific studies using poultry are easier and
less costly to perform than on large ruminants or pigs. One of the more frequently cited
studies is that of Kana et al. (2010) who systematically fed two different biochars, one
from corncobs and the other from canary tree (Bakeridesia integerrima) seeds, to broiler
chickens at different feeding concentrations from 0% to 1% per kg feed. Unfortunately,
the production of biochar was only designated as “traditional”and was not described
in detail, but the high ash levels of 47% and 25%, respectively, indicate that a substantial
portion of the initial biomass was burned and not fully pyrolyzed. Nevertheless,
feeding both biochars up to 0.6% led to greater, mostly significant weight gain, while
the higher dosages led to no further significant weight gain, but also to no weight loss
compared to the control. Liver weight, abdominal fat nor bowel length and weight were
affected by the biochar feeding. The study is an important indication that biochar
derived from non-woody biomass and with a higher ash content may also be suitable
for feeding, which is so far not allowed by the European Biochar Foundation (EBC) (2012).
In a later study with the same biochars, the authors examined whether chickens can,
thanks to the biochar supplement, be fed with 20% chickpeas, a feed that is protein-rich
but generally difficult for chickens to digest. Surprisingly, when the ash-rich biochar
from corncobs was added, the boiled chickpeas could be fed and provided the same weight
gain in the broilers as the control without chickpeas. However, the lower-ash biochar from
the tree seeds did not show the same effect here (Kana, Teguia & Fomekong, 2012).
Bakr (2007) used traditionally produced citrus wood charcoal purchased at the local
market in Nablus and added them at very high dosages of 0%, 2%, 4% and 8% to the
standard broiler feed. At 2%, significant increases on body weight, feed intake and feed
efficiency were measured during the first three weeks compared to control. After this initial
period, all results were similar. Of particular note in this study is that even the very
high feeding dosage of 8% of a biochar of at least doubtful quality did not cause any adverse
effects. Kutlu, Ünsal & Görgülü (2001) also used very high biochar dosages of up to 10%
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 25/54
of the base diet, and found that all dosages significantly increased basal feed intake in the
first 28 days, and also weight gain and feed efficiency of both broilers and laying hens
but did not show significantly higher gains after this initial period.
A Polish working group led by Teresa Majewska conducted several feed trials on
chickens and turkeys between 2000 and 2012 (Majewska & Pudyszak, 2011;Majewska,
Mikulski & Siwik, 2009;Majewska, Pyrek & Faruga, 2002). They achieved consistently
positive results with doses of 0.3% of a hardwood biochar. They not only found higher
weight gain and better feed efficiency, but also higher protein levels in the pectoral muscles
and a significantly lower mortality compared to the control. Majewska et al. explained
these improvements by (1) the detoxification of feed components, (2) the reduction in
surface tension of the digestive pulp and (3) the improvement in fat loss in the liver.
Ruttanavut et al. (2009) did not find a statistically significant increase in duck growth
when co-fed with a 1% biochar—wood vinegar blend, but they showed significant biochar
effects on the size of the villi, the cell surface, and the rate of cell division in the gut,
which confirms similar results from literature (Samanya & Yamauchi, 2001;Ruttanawut,
2014). Islam et al. (2014) showed in an experiment with 150 young ducks that
feeding with 1% of a 1:1 mixture of biochar and sea tangle (Laminaria japonica) can be
recommended as an alternative to the use of antibiotics in the feeding of ducks.
Several research groups have shown that the quality of chickens’meat can be
significantly improved by feeding of biochar (Cai, Jiang & He, 2011;Kim et al., 2011;
Yamauchi, Ruttanavut & Takenoyama, 2010;Yamauchi et al., 2014). It was for example
found that no significant weight gain was recorded when fed with 0.5% activated coconut
shell biochar but that Serum Glutamine, Oxaloacetic Transminase, Serum Glutamine
Phosphate Transminase, Albumin and triglycerides as well as sensory evaluation and
weight of abdominal fat, heart and spleen significantly improved while the cholesterol level
decreased (Jiya et al., 2013,2014). Also, when broiler chickens were fed with 1% activated
biochar the useful fatty acid, oleic acid and total mineral content of the meat increased
significantly (Park & Kim, 2001). Other trials with 2% biochar or a mixture of bamboo
biochar and wood vinegar did not show significant differences in meat quality compared
to controls (Sung et al., 2006;Fanchiotti et al., 2010;Ruttanawut, 2014).
It was observed in several studies that the strength of eggshells can be improved by
co-feeding biochar (Kutlu, Ünsal & Görgülü, 2001;Ayanwale, Lanko & Kudu, 2006;
Kim et al., 2006). Yamauchi, Ruttanavut & Takenoyama (2010) found an increase in egg
production of nearly 5% when hens were fed with a blend of bamboo biochar and wood
vinegar. The collagen content of the eggs increased highly significantly by 33% with a
1% feed of the same bamboo biochar—wood vinegar mixture. Collagen not only increases
the shelf life of the eggs but is also an interesting ingredient for pharmaceuticals and
cosmetics (Yamauchi et al., 2013).
Prasai et al. (2016) investigated biochar, bentonite and zeolite for selective pathogen
control in hens. Their treatments involved the commercial layer diet (control group)
amended with biochar, bentonite and zeolite at 4% w/w, respectively. While bird weight
and number of eggs did not differ significantly between the control and the biochar
treatment, the total egg weight increased by 5% and the feed conversion ratio increased by
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 26/54
12% compared to the control. Feeding bentonite and zeolite revealed comparable increases
and non-significant differences to biochar, respectively. The biochar feed amendment
did not result in altered gut microbial community richness and diversity compared to the
control. However, individual phylotypes at different phylogenetic levels did respond
differently to the three amendments and reduced especially the abundance of Helicobacter
and Campylobacter. Both genera are gram-negative and include multiple pathogenic
species. The authors demonstrated that biochar, bentonite and zeolite can be used to
selectively reduce the abundance of some major poultry zoonotic pathogens without
reducing chicken microbiota diversity or causing major shifts in the gut microbial
community and are thus a viable alternative to antibiotics in the poultry industry. A recent
Vietnamese study on supplementing chicken feed with 1% rice husk biochar confirmed
positive effects on pathogen occurrence with reduced plasma triglycerides, total
coliform bacteria in litter and E. coli in feces (Hien et al., 2018). However, no impact on
live weight gain, feed consumption and feed conversion ratio were observed.
In Switzerland, two groups of 400 broilers were fed for 36 days with a 0.7% biochar
supplement provided as a commercial feed additive mixture that had undergone a lactic
fermentation beforehand (Kupper et al., 2015). The biochar treatment did not reveal
any significant difference in daily weight gain, feed consumption, feed conversion rate or
food pat and hook lesions compared to the two control groups that received the same
feed without the biochar containing supplement. Moreover, no significant difference in
NH
3
-emissions of the stored or field applied broiler manure was measured. The results of
Kupper et al. (2015) are in puzzling contradiction with a similar trial in the same country
undertaken at the Swiss Aviforum where groups of 270 broilers with four replicates
were fed for 37 days with the same 0.9% biochar based commercial feed additive, with
1% pure wood based biochar (HTT of 700 C) or with 0% biochar as control group
(Albiker & Zweifel, 2019). Here, the weight gain increased significantly by 5% (fermented
biochar product) and 6% (pure biochar) compared to the control. Moreover, both biochar
treatments decreased the foot pat and hook lesions by 92% and 74%, respectively,
compared to the control.
For a study at West Virginia University with test groups of 1,472 broiler chicks (N= 8),
pyrolyzed poultry manure was provided as feed additive despite insufficient feed quality
analyses (Evans, Boney & Moritz, 2016). The arsenic content of the poultry manure
biochar exceeded the threshold of the European Biochar Feed Certificate (European
Biochar Foundation (EBC), 2018) by a factor of 6.5, and no PAH analyses were carried out,
despite using gasification technology that is known for the risk of producing biochars with
high levels of PAH contaminations which often exceed threshold values of the EBC by
factor 100 and more (Hilber et al., 2012;Bucheli, Hilber & Schmidt, 2015). Irrespective of
these issues, supplementing poultry manure biochar at 2% increased the feed conversion
ratio by 7% while at 4% biochar supplementation the life weight gain decreased by 8% both
compared to the control. No other investigated parameter showed significant differences
to the control over the 21-day experimental period. The feeding of such pyrolyzed
material is in several regards not in agreement with the EBC-feed standard, and feeding
uncharacterized excrement-based materials is certainly not up to ethical standards.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 27/54
In an Australian trial, groups of 20 layer hens (N= 4) were fed a biochar made at 550 C
from green wood waste at rates of 0%, 1%, 2% and 4%, respectively (Prasai et al., 2018a)
for 25 weeks. While no significant difference in weight gain was observed, the feed
conversion ratio improved significantly between 10% and 13% in the three biochar
treatments compared to the control without biochar. The egg weight was 5% higher in the
2% biochar treatment and 4% higher in the 4% treatment compared to the control.
Standardized indicators of egg quality (i.e., Haugh unit, Albumen height, stability of egg
shell) where not changed by the biochar feed amendment. The Yolk color index,
however, decreased with increasing biochar dosage. The same effect was also found
when bentonite or zeolite was used instead of biochar. Yolk color is mainly the result of
carotenoid content (Bovšková, Míková & Panovská, 2014). Carotenoids are lipophilic
organic molecules that accumulated from the feed. Thus, we hypothesize that biochar may
sorb a certain amount of lipophilic ingredients of the feed. The N-balance between feed-N
intake, egg-N, excreta-N and lost N did not differ significantly between the treatments
though the excreta-N was reduced by 20–34% in the 2% and 4% biochar treatment
compared to the control. The lower recovery of N in excreta is indicative of a more efficient
digestive extraction of N, consistent with the observed higher feed conversion efficiency.
Remarkably, the inclusion of 2% and 4% biochar maintained egg production at
normal levels when birds were challenged with fungal-contaminated feed. In the control
treatment, the contaminated feed led to decreased egg production by 16%. The same
main author found, in another publication based on a similar trial with the same 1%,
2% and 4% biochar amendments, improvements of the poultry manure especially in regard
to granule size, water retention and decomposition characteristics (Prasai et al.,
2018b). N-contents in the decomposed poultry manure were lower by 20% and 26%,
respectively, in the treatment with 2% and 4% biochar feed compared to the control.
NH
3
-emissions of the manure, measured in a separate experiment using incubated bell
jars, increased by 31% in the treatments with 2% and 4% but not with 1% biochar
feed amendments compared to the control. This increase in ammonia emissions due to
high doses of poultry feed applied biochar is puzzling as the addition of higher dosages
(5–15% (m/m)) of biochar to poultry manure composting was shown to decrease
ammonia emissions between 53% and 89% (Rong et al., 2019). Apparently, biochar affects
poultry manure composting differently when applied to the feed versus when applied
directly to the manure.
Aquaculture
Nowadays aquaculture provides as much product for human consumption as capture
fisheries, yet it causes considerable harm to the environment if effluents with fish feces and
excess feed nutrients are not treated and recycled into valuable fertilizers (UN, 2016).
Biochar supplements have been fed to fish with the intention to improve water quality
as well as fish health and productivity. Japanese flounder were fed with 0–4% incremental
doses of a bamboo biochar mixed into the regular feed (Thu et al., 2010). While all biochar
feed additions resulted in significantly higher flounder weight gains, the variability of
individual results was so high that only the 0.5% dose provided statistically significantly
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 28/54
higher weight gain rates of 18%. It was noteworthy that all biochar feeding rates resulted in
significantly lower nitrogen excretions and reduced the nitrate content in the fish water
by >50%. In a South Korean experiment also with flounder, dosages from 0% to 2%
of a biochar—wood vinegar blend were fed. At a dose of 1%, the feed efficiency increased
significantly by 10%, and also the total weight gain of the fish was significantly higher
(Yoo, Ji & Jeong, 2007). The authors concluded that feeding rates between 0.5% and 1% of
DM feed intake may deliver maximum weight gain and feed efficiency.
Two different biochars, one made from rice husks in a TLUD stove (Anderson, Reed &
Wever, 2007) and one made from wood in traditional charcoal kilns, were compared
as a 1% feed additive for tank raised striped catfish (Pangasius hypophthalmus)
(Lan, Preston & Leng, 2018). Growth rates increased by 36% with the rice husk biochar and
44% with the wood biochar compared to the control. Both biochars led to 25% increased
ratio of weight to length indicating an enhanced flesh to bone ratio due to the faster
growth rate caused by the biochar additive. Water quality improved significantly as levels
of ammonia nitrogen, nitrite, phosphate and chemical oxygen demand decreased by
24%, 22%, 15%, 21%, respectively, in the rice husk biochar treatment with similar values
for the other biochar. The authors hypothesized that biochar may facilitate the formation
of biofilms as habitat for gut microbiota which could be the explanation for the
improved growth rates.
In China, a dietary bamboo biochar was added to the feed of juvenile common carps
at rates from 1% to 4% (Mabe et al., 2018). The biochar treatments did not produce
any obvious effect on the growth performance of the carps compared to 0% control.
However, significant improvements were reported on serum indicators such as alanine
aminotransferase, aspartate aminotransferase, total protein, triglycerides, total cholesterol,
high density lipoprotein (HDL) and glucose, demonstrating an increase in fish quality
and health. The most beneficial effects were found at the highest biochar dosage.
No adverse effects were observed.
Reduction of methane emissions from ruminants
Ruminant production accounts for about 81% of the total GHG from the livestock sector
(Hristov et al., 2013). While in chickens, pigs, fish and other omnivores most of the
greenhouse gas emissions are caused by the decomposition of solid and liquid excretions,
ruminants’GHG emissions are mainly produced by direct gaseous excretions through
flatulence and burping (eructation). The latter mainly affects cattle which are capable of
producing 200–500 l of methane per day (Johnson & Johnson, 1995). These methane
emissions, mainly produced through rumen microbial methanogenesis, are responsible for
90% of the GHG caused by cattle (Tapio et al., 2017).
In the bovine rumen, methanogenesis is carried out by archaea that convert microbial
digestion products H
2
and CO
2
or formate (HCOOH, methanoate) to CH
4
to gain energy
under anoxic conditions. While hydrogen serves as an electron donor for the microbial
reduction of CO
2
to methane (CH
4
), the reduction of formate (requiring six electrons to be
reduced to H
2
and CO
2
) can have several biochemical pathways. The production of
methane means a significant loss of energy for the animal (from 2% to 12% of the total
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 29/54
energy intake; Tapio et al., 2017) as the high-energy methane cannot be digested any
further and has to be eliminated almost entirely through eructation (burp) and only
minimally via flatulence from the digestive tract (Murray, Bryant & Leng, 1976). Since
methane is a 28–34 times more harmful than CO
2
(global warming potential with and
without climate-carbon feedbacks over a period of 100 years; Myrhe et al., 2013),
there is an increasing interest in feed supplements that not only increase feed efficiency,
but also can reduce methane emissions resulting from ruminant digestion.
Numerous studies have sought to find other electron acceptors besides CO
2
and enteric
fatty acids to reduce methanogenesis. However, until recently, apart from the addition
of nitrate and sulfate reacting to ammonia and hydrogen sulfide, respectively, which are
toxic for the animals in higher concentrations, no convincing options have been found to
date (Van Zijderveld et al., 2010;Lee & Beauchemin, 2014).
The first evidence that biochar might act as an electron acceptor and reduce methane
production in the rumen came from Vietnam in 2012 (Leng, Inthapanya & Preston, 2012;
Leng, Preston & Inthapanya, 2012). In vitro studies revealed that 0.5% and 1% biochar
additions to the ruminal liquid significantly reduced methane production by 10% and
12.7%, respectively. Higher levels of biochar did not further reduce methane production.
All experiments were conducted in the presence of 2% urea as a non-protein source of
nitrogen. When urea was replaced with nitrate (6% of DM feed intake as KNO
3
to supply
the same amount of N), methane production decreased by up to 49%.
While both, nitrate and biochar, may act as electron acceptor in the rumen and likely
explain at least part of the effect, it is difficult to elucidate on the base of the data provided
why the methane reductions by nitrate (-29%) and biochar (-22%) were higher when
fed combined (-49%). However, as the effect appears dosage independent (0.5% or
1% biochar) it is unlikely that the two substances reduce methane production by the
same mechanisms. It may be hypothesized that the biochar acts as a redox-active electron
mediator that takes up electrons from microbial oxidation reactions (e.g., oxidation of
acetate to CO
2
) and donates the electron at a certain distance from the microbial reaction
center (at another spot of the same biochar particle) to mediate an abiotic reduction of
nitrate (Saquing, Yu & Chiu, 2016). Biochar at feeding ratios of about 1% (100 g/day)
would not have the capacity to act as terminal electron acceptor for all rumen produced
hydrogen considering a daily production of about 200 l methane for the various studies
of Leng, Inthapanya & Preston (2012) in SE-Asia and up to 500 l methane for typical cattle
in Europe or the US. Nitrate (at 6% of DM intake) would have this capacity as terminal
electron acceptor but is not efficient as direct electron acceptor in microbial oxidation
reaction due to the toxic effects of its reaction products (i.e., nitrite and ammonia).
Another likely mechanism is the biotic reduction of nitrate through Methylomirabilis
oxyfera-like bacteria using the supplemented nitrate as an oxygen source for methane
oxidation in the rumen. Denitrifying anaerobic methane oxidizing (DAMO) bacteria like
Candidatus Methylomirabilis oxyfera belonging to the NC10 phylum were shown to
efficiently oxidize methane anaerobically in deep lake sediments (Deutzmann et al., 2014).
NC10 DAMO bacteria were equally found in wetlands (Shen et al., 2015), in grassland
soils used for animal husbandry (Bannert et al., 2012), and with a robust abundance
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 30/54
of 3.8 10
5
to 6.1 10
6
copies g
-1
(dry weight) in flooded paddy fields (Shen et al., 2014).
DAMO bacteria were further found in the rumen fluid of Xinong Saanen dairy goats
in Southern China. The proportion of NC10 in total bacteria in the rumen fluid was 10%,
and it could clearly be seen that NC10 mediated nitrate reduction led to reduced
enteric methane emissions (Shen et al., 2016). Notwithstanding further evidence, it may be
hypothesized that the additional effect of combined biochar and nitrate supplements is
due to the biotic denitrifying methane oxidation that might further be enhanced
through electron accepting and redox mediating properties of the biochar. Systematic
investigations to better understand the likely mechanisms are urgently needed.
In vivo experiments showed that methane formation in cattle could be reduced by 20%
when 0.6% of biochar was added to the ordinary compound feed (Leng, Preston &
Inthapanya, 2013). When the same amount of biochar was combined with 6% potassium
nitrate, methane emissions decreased by as much as 40%. In addition to reducing
methane emissions, highly significant bovine weight gain (+25%) was observed in the
experiment as compared to the control, suggesting an increase in feed efficiency and/or
reduced energy conversion losses. The biochar in this and the earlier in vitro trial was
produced at high temperatures (HTT = 900 C) from silicon-rich rice husks, which
suggests a high electrical conductivity and electron buffering capacity (Yu et al., 2015;
Sun et al., 2017) which may lead to greater efficiency of fodder-decomposing redox
reactions. Leng, Inthapanya & Preston (2013) have further shown that different biochars
have different effects on methane emissions. A likely reason for this are differences in
electrical conductivity and in electron buffering (Sun et al., 2017) depending on the
biomass and pyrolysis temperature, which determine the biochar’s properties of
transmitting electrons between different bacterial species.
Leng, Inthapanya & Preston also examined the rumen fluid of cattle previously fed with
and without biochar. They found that rumen fluid from cows that had been fed biochar
produced less methane than rumen fluid from non-biochar-fed cattle. This suggests
that the animals fed biochar may have had a different microbial community in the rumen
(Leng, Inthapanya & Preston, 2012). Phanthavong et al. (2015) also found a significant
decrease in methane emissions over a 24-h period in in vitro tests with 1% biochar added
to a manioc root feed mix, but only by about 7%.
In 2012, a Danish team of researchers led by Hanne Hansen published the results of an
in vitro study with large doses of various, but poorly characterized biochars and their
effects on methane production of rumen fluids (Hansen, Storm & Sell, 2012). All tested
biochars (made from wood or straw with slow pyrolysis or gasification) tended (p= 0.09)
to reduce methane emissions from 11% to 17%, with an activated biochar showing
the highest reduction rate. However, the enormously high addition of 9% cannot be
considered as viable as this would surely impact feed digestibility on the long term.
Winders et al. (2019) did not detect any significant reductions on methane emissions in
steers over a 23 h period when using the more realistic biochar supplement rates of
0.8% and 3%.
Four biochars (from pine wood chips and corn stover, each pyrolyzed at 350 and
550 C) were co-fermented at rates of 0.5%, 1%, 2% and 5% in ryegrass silage and used as
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 31/54
feed substrates in an in vitro trial with rumen liquid (Calvelo Pereira et al., 2014).
None of the biochar treatments revealed any effect on methane production as compared to
the control.
Due to the promising results of Leng, Inthapanya & Preston (2012) several other
research groups have carried out in vitro experiments though without obtaining significant
results which, therefore, where not published (Belgium, USA and Germany, Hans-Peter
Schmidt, 2018, personal communications). Until today, only the research group of Ron
Leng were able to produce and reproduce high reduction rates of methane production
both in vitro and in vivo. It is impossible yet to identify a convincing reason or mechanism
to explain the strong divergence of the results. It might be due to the particular 900
gasifier rice-husk biochar or to the non-common feed used in their trials (tannin rich
cassava roots and foliage that may provide terminal electron acceptors) or the particular
rumen microbiota of the South-East Asian cattle that may contain higher rates of DAMO
bacteria. The experiments from Europe, New Zealand and America with conventional
cattle fodder and standard biochar prudently suggested, that biochar alone (i.e., without
nitrate as oxygen source or terminal electron acceptor) may not live up to the expectations
to reduce enteric methane emission of cattle (Table 2).
This conclusion is confirmed by a recent and perhaps the most systematic and complete
in vitro study to date, at the University of Edinburgh (Cabeza et al., 2018). The authors
investigated the effects on in vitro rumen gas production and fermentation characteristics
of two different rates of biochar (10 and 100 g biochar/kg substrate, i.e., 1% and 10%)
made at two different temperatures (HTT 550 or 700 C) and from five different biomass
sources (miscanthus straw, oil seed rape straw, rice husk, soft wood pellets and wheat
straw). The methane production was reduced by all biochar treatments and at both
concentrations levels by about 5% compared to the control without biochar. There was no
significant difference between the different types and amounts of biochar. The absence
of significant differences between those very different biochars is puzzling though an
important milestone towards the understanding of biochar’s mechanisms in animal
digestions because there has to be a common cause leading to the same effect between
all these different biochars.
A new perspective on the subject was recently put forth by Saleem et al. (2018) who
used an artificial semi-continuous rumen system to test the effect of a high temperature
biochar that was post-pyrolytically treated to acidify the biochar to a pH of 4.8. For a
high-forage based diet, 0.5%, 1% and 2% of this acidic biochar reduced methane
production by 34%, 16% and 22%, respectively. All other biochars in all of the experiments
reviewed here were alkaline (pH between 8 and 11.5). The acidification of biochar not
only oxidizes the carbonaceous surfaces and makes the biochar hydrophilic, it also modifies
the redox behavior and thus its “affinity”for microbial interaction. As this is, to our
knowledge, the first and only experiment to demonstrate a reduction of methane emissions
using acidified biochar and as there are no systematic investigations about the acidification
effect yet, it is too early to draw a definitive conclusion. However, it is an indication that
post-pyrolytic treatment of biochar has the potential to design and optimize the biochar
effects in animal digestion, and, notably, to reduce enteric methane emissions.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 32/54
The promising results of Leng, Inthapanya & Preston (2012) when feeding biochar in
combination with nitrate call for systematic investigations of (1) pyrolytic and post pyrolytic
treatments (e.g., pyrolysis temperature, activation, acidification), (2) feed blending with
terminal electron acceptors (e.g., nitrate, urea and humic substances; Md Shaiful Islam et al.,
2005), (3) co-feeding with oxygen sources for anaerobic methane oxidation (nitrate) and
(4) inoculation with Methylomirabilis oxyfera-like bacteria to oxidize methane.
Possible side effects of biochar
Based on the literature compiled in the present review, none of the activated and non-
activated biochars used as feed additive or veterinary treatment had toxic or negative
effects on animals or the environment. No negative side effects were reported either in
short-term or long-term administration trials.
There are a growing number of farmers that have been feeding their livestock with
biochar additives on a daily basis for several years without noticing negative side-effects
(Kammann et al., 2017; C. Kammann et al., 2017, personal communications).
Table 2 Overview of published studies about biochar effects on enteric methane emissions.
Daily BC intake/content
of rumen liquid
Type
of trial
Feedstock HTT in C Activation Blend CH
4
-reduction Source
0.5% to ruminal liquid In vitro Rice husk 900 No 2% urea 10% Leng, Inthapanya &
Preston (2012)
1% to ruminal liquid In vitro Rice husk 900 No 2% urea 12.7% Leng, Inthapanya &
Preston (2012)
1% to ruminal liquid In vitro Rice husk 900 No 6% KNO
3
49% Leng, Inthapanya &
Preston (2012)
0.6% of feed DM In vivo Rice husk 900 No 20% Leng, Preston &
Inthapanya (2013)
0.6% of feed DM In vivo Rice husk 900 No 6% KNO
3
40% Leng, Preston &
Inthapanya (2013)
1% of feed DM In vivo Rice husk 900 No Manioc
root
feed
7% Phanthavong et al.
(2015)
9% to ruminal liquid In vitro Wood/straw Partly n.s. (11–17%) Hansen, Storm & Sell
(2012)
1% of DM feed In vivo Wood >600 n.s. Winders et al. (2019)
0.5%, 1%, 2%, 5% of
rumen incubation
In vitro Wood/corn
stover
350/550 Ensiled Mixed to
ryegrass
before
ensiling
n.s. Calvelo Pereira et al.
(2014)
1%, 10% of DM feed In vitro Miscanthus straw/
oil seed rape
straw/rice husk/
soft wood pellets/
wheat straw
550/700 No 5% Cabeza et al. (2018)
0.5%, 1%, 2% of DM feed In vitro pine 400–600 Acidification
to pH 4.8
34%, 16%, 22% Saleem et al. (2018)
Note:
The table indicates the reductions of enteric methane emissions of cattle due to biochar feed supplements or additions to rumen liquids summarizing biochar dosages,
pyrolysis feedstock and temperature and post-pyrolytic treatments.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 33/54
However, there are only very few if any long term biochar feeding trials with clinical
follow-up (Struhsaker, Cooney & Siex, 1997;Joseph et al., 2015b). In the absence of clinical
long-term feeding trials with biochar, long-term experiments with oral administration
of activated carbon to humans seem to indicate rather low risks. The administration
of 20–50 g activated biochar daily in uremia patients for 4–20 months did not produce
significant side effects (Yatzidis, 1972). Olkkola & Neuvonen (1989) maintained dosages of
10–20 g administered three times a day over a period of several months in human patients
without negative side effects.
The main risks of long-term biochar feeding may arise (1) from shifting microbial
species composition in the digestion system (microbiome) and (2) from the potential
adsorption of essential feed compounds and/or drugs. Only a few scattered studies have
addressed both points.
With regard to the microbiome, the adsorptive capacity of activated biochar for the
beneficial bacterial flora in the digestive tract of dairy cows was examined using
gram-positive Enterococcus faecium,Bifidobacterium thermophilum and Lactobacillus
acidophilus (Naka et al., 2001). Although activated biochar certainly adsorbs strains of
the normal, healthy bacterial flora too, adsorption of these bacterial strains was
significantly lower than the adsorption of the dangerous E. coli O157: H7 strain, which
is gram-negative. Biochar appeared to positively affect the ratio of (certain) beneficial
bacterial flora to (certain) pathogenic flora. However, it must be systematically
investigated and mechanistically understood for a much larger number of digestive and
pathogenic microorganisms, before a more general conclusion can be drawn. Our review
suggests that the impact of biochar on microorganisms depends on the cell envelope,
that is, the gram-stain with gram-positive (plasma membrane plus 20–80 nm of
peptidoglycan) not being or being less well sorbed to biochar, while gram-negative
bacteria (plasma membrane plus 10 nm peptidoglycan plus outer membrane) are better
sorbed. However, the structure of the cell envelope and the fact of being gram-positive
or negative does not, on its own, indicate whether a bacteria is a pathogen or not.
The potentially selective action of biochars on various bacterial genera opens up the
possibility of inoculating the biochar as a carrier matrix with beneficial bacteria, for
example, to administer gram-positive Lactobacilli. to positively influence the intestinal
flora (Naka et al., 2001). Different groups of authors have found that pathogens are
generally bound more strongly than the native intestinal flora to biochar in the digestive
tract (Naka et al., 2001;Watarai, Tana & Koiwa, 2008;Choi et al., 2009;Chu et al.,
2013a). The hypotheses put forward indicate a possible correlation with more favorable
pore size distribution for the adsorption of pathogens, as well as the observation of the
(nonspecific) promotion of beneficial microorganisms such as Lactobacilli. This
combination could positively target the digestive milieu and suppress pathogens.
With regard to sorption, biochar can work against human poisoning and drug overdose
(Park, 1986), but thus could also counteract intended benefits of drugs. Based on our
review, the same can be proclaimed regarding pharmaceuticals used to treat livestock. It is
evident that acute, temporary treatment and continuous addition to feed over years do
not underlie the same risk assessment. Fujita et al. (2012) conducted a comprehensive
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 34/54
study in 2011, where they examined the influence of biochar feeding on hens’health and
egg quality. Histopathological studies showed no changes in the digestive tract or in the
liver. Examination of the egg yolk showed that fat-soluble vitamins A and D3 did not show
a statistically significant trend towards lower concentrations, but that the vitamin
E content in the eggs was reduced by about 40% when hens were fed daily with 0.5%
biochar (Fujita et al., 2012). Although all other quality parameters such as fatty acids,
oxidative stability and mineral content in the eggs were not affected by biochar feeding,
it was the first evidence that a beneficial compound like a vitamin can be significantly
reduced by co-feeding biochar. The above mentioned reduction of carotenoids in egg
yolks indicated by changes in yolk color (Prasai et al., 2018a) further supports the
conclusion that systematic research with well-defined biochars and a focus on liposoluble
feed ingredients like vitamin E and carotenoids is needed before industrial scale-up of
long-term biochar co-feeding can be safely recommended. However, compared to a large
spectrum of other feed additives and ubiquitous pesticide and mycotoxin contamination
of animal feed, risks of quality-controlled biochar feed can be considered low, even
when supplemented on a regular basis.
Administration of biochar feed and biochar quality control
Biochar should not be fed without complete biochar analysis and control of all relevant
parameters of current feed regulations such as provided by the European Biochar
Feed Certificate (European Biochar Foundation (EBC), 2018). The analysis should be
carried out by an accredited laboratory specialized in biochar and feed analytics. In
addition, as required by the EBC, biochar should always be processed and administered
moist to avoid the formation of dust (European Biochar Foundation (EBC), 2012). If this is
respected, biochar can be added to all common feed mixes and is usually mixable with all
common feeds. Feed quality biochar may also be added to animal drinking water and,
in the case of acute intoxication, activated biochar should be administered in aqueous
suspension (Neuvonen & Olkkola, 1988). Depending on livestock species, the biochar may
also be provided in freely accessible troughs on the pasture or in the stable, without
previous mixing into daily feed. Often, the biochar is mixed with popular supplements
such as molasses (Joseph et al., 2015b)orflavoring such as saccharin, sucrose and the like
(Cooney & Roach, 1979). Some German and Swiss farmers inject 1% (vol) of biochar into
silage towers or silage bales via automated equipment (O’Toole et al., 2016).
In many of the experiments cited here, biochar was not administered alone, but in
admixture with other functional feed supplements such as humic acid, wood vinegar,
sauerkraut juice, eubiotic liquids, stevia, nitrate or tannins, the effect of the mixture
often being greater than with separate feeding of the individual components. Those
combinations of biochar with various other feed supplements open a huge scope for
further research and the reasonable expectation that suitable feed mixtures can be
developed for specific purposes and animal species.
The adsorption capacity of biochar depends in particular on the specific surface area,
surface charge and the pore size distribution. Activation of biochar significantly increases
the specific surface area (from approx. 300 m
2
to >900 m
2
), but the increase in surface
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 35/54
area is mainly due to the opening of micropores (<2 nm). These micropores are mostly
too small for the higher molecular weight substances or bacterial pathogens relevant for
animal digestion. Galvano et al. (1996b) found that biochar with dominating micro
porosity (<2 nm) had lower adsorption capacities for mycotoxins due to slow diffusion of
these toxins into the pore-system. This was also the case for other investigated toxic
compounds such as pesticides, PCBs, dioxins or pathogens, as was demonstrated by
Edrington et al. (1997) when highly activated biochar did not reduce the toxic effects of
aflatoxin in chickens more strongly than non-activated biochar. Therefore, the activation
of biochar may not significantly increase the specific adsorption capacity for certain
target substances or organisms. To produce a biochar with a particularly high content
of accessible meso and macro pores, downstream activation is not necessary and can
be achieved merely by adjusting the pyrolysis parameters. Generally speaking, a higher
meso-porosity is achieved at pyrolysis temperatures above 600 C(Brewer et al., 2014).
Depending on the activation method, biochar activation and acidification can greatly
modify the electron (and proton) mediating capacity (Chen & McCreery, 1996), however,
to date no systematic research has been done with such modified biochars in animal
feeding. Currently, only pyrolysis temperature was identified as main driver for the redox
behavior, revealing temperatures between 600 and 800C as optimal (Sun et al., 2017).
To minimize condensate deposition on biochar surfaces and to ensure that PAH
contents stay below common thresholds (European Biochar Foundation (EBC), 2012)
sufficient active degassing of the cooling biochar at the end of the pyrolysis process is
mandatory, for example, by using inert gas or by sufficient counter flow ventilation during
discharge (Bucheli, Hilber & Schmidt, 2015).
Biochars used in the various studies were mainly derived from wood, but also from
coconut shells (Jiya et al., 2013), rice husk (Leng, Preston & Inthapanya, 2013), shea butter
stocks (Ayanwale, Lanko & Kudu, 2006), bamboo (Van, Mui & Ledin, 2006;Chu et al.,
2013a), corn stover (Calvelo Pereira et al., 2014), corncob (Kana et al., 2011), straw (Cabeza
et al., 2018) and many other types of biomass. According to current publications, there is no
scientific basis to prefer one source of biomass over another to produce feed-grade biochar. As
long as important guidelines for the H/C
org
ratio (= degree of carbonization), carbon and
heavy metal contents, PAHs and other organic pollutants are met, biochar from woody as
well as non-woody precursors may safely be used for co-feeding purposes.
The European Biochar Certificate (EBC), a voluntary industry standard, has been
controlling and certifying the quality of biochar for use in animal feed since January 2016
(European Biochar Foundation (EBC), 2018). To date, six biochar producing companies
have obtained the EBC-feed certificate (European Biochar Foundation (EBC), 2013).
The EBC Feed Certificate guarantees compliance with all feed limits prescribed by the EU
regulations and, moreover, certifies sustainable, climate friendly production (European
Biochar Foundation (EBC), 2018).
CONCLUSIONS
The use of biochar as a feed additive has the potential to improve animal health, feed
efficiency and livestock productivity, to reduce nutrient losses and greenhouse gas
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 36/54
emissions and to increase manure quality and thus soil fertility. In combination with other
good farmer practices, biochar could improve the overall sustainability of animal
husbandry. The analysis of 112 scientific papers on biochar feed supplements has shown
that in most studies and for all farm animal species, positive effects on different parameters
such as growth, digestion, feed efficiency, toxin adsorption, blood levels, meat quality
and/or emissions could be found. However, a relevant part of the studies obtained results
that were not statistically significant. Most importantly, no significant negative effects on
animal health were found in any of the reviewed publications.
It is undeniable that, despite the large number of scientific publications, further
research is urgently needed to unravel the mechanisms underlying the observed results
and to optimize biochar-based feed products. This applies in particular to the
characterization of the biochar itself, which in the majority of studies was insufficiently
analyzed. The electrochemical interaction of biochar and organic systems is extremely
complex and needs considerable more fundamental research and systematic in vivo
trials. Moreover, if biochar’s role within animal digestion is mainly to act as a mediator
and carrier substance, the combination with otherfeedadditivesandinoculantsmaybe
mandatory to achieve the full functionality of biochar for its beneficial use in animal
digestion and animal health.
Based on the scientific literature published so far, it can be concluded that (1) a general
efficacy of biochar as feed supplement can be observed and (2) biochar feeding can be
considered safe at least for feeding periods of several months. Despite this positive
assessment, regular feeding of biochar should never induce livestock farmers to
compromise on the quality of feed and animal welfare standards.
ADDITIONAL INFORMATION AND DECLARATIONS
Funding
This study was financed by the BioC project of the r4d call of the Swiss National
Science Foundation. Claudia Kammann received financial support from the BMBF-funded
project BioCAP-CCS, grants no. 01LS1620A and 01LS1620B. The funders had no role in
study design, data collection and analysis, decision to publish, or preparation of the
manuscript.
Grant Disclosures
The following grant information was disclosed by the authors:
BioC project of the r4d call of the Swiss National Science Foundation.
BMBF-funded project BioCAP-CCS: 01LS1620A and 01LS1620B.
Competing Interests
The authors declare that they have no competing interests. Hans-Peter Schmidt and
Nikolas Hagemann are employed by Carbon Strategies, Ithaka Institute. Nikolas
Hagemann is employed by Agroscope. Kathleen Draper is the director of Ithaka Institute
for Carbon Intelligence.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 37/54
Author Contributions
Hans-Peter Schmidt conceived and designed the experiments, analyzed the data,
prepared figures and/or tables, authored or reviewed drafts of the paper, approved the
final draft.
Nikolas Hagemann analyzed the data, authored or reviewed drafts of the paper,
approved the final draft.
Kathleen Draper analyzed the data, authored or reviewed drafts of the paper, approved
the final draft.
Claudia Kammann conceived and designed the experiments, analyzed the data, authored
or reviewed drafts of the paper, approved the final draft.
Data Availability
The following information was supplied regarding data availability:
There were no raw data used in this literature review.
REFERENCES
Abit SM, Bolster CH, Cai P, Walker SL. 2012. Influence of feedstock and pyrolysis temperature of
biochar amendments on transport of Escherichia coli in saturated and unsaturated soil.
Environmental Science & Technology 46(15):8097–8105 DOI 10.1021/es300797z.
Abit SM, Bolster CH, Cantrell KB, Flores JQ, Walker SL. 2014. Transport of Escherichia coli,
Salmonella typhimurium, and microspheres in biochar-amended soils with different textures.
Journal of Environmental Quality 43(1):371–388 DOI 10.2134/jeq2013.06.0236.
Ademoyero AA, Dalvi RR. 1983. Efficacy of activated charcoal and other agents in the
reduction of hepatotoxic effects of a single dose of aflatoxin b1 in chickens. Toxicology Letters
16(1–2):153–157 DOI 10.1016/0378-4274(83)90024-3.
Aeschbacher M, Vergari D, Schwarzenbach ŔP, Sander M. 2011. Electrochemical analysis of
proton and electron transfer equilibria of the reducible moieties in humic acids. Environmental
Science & Technology 45(19):8385–8394 DOI 10.1021/es201981g.
Al-Kindi A, Schiborra A, Buerkert A, Schlecht E. 2017. Effects of quebracho tannin
extract and activated charcoal on nutrient digestibility, digesta passage and faeces
composition in goats. Journal of Animal Physiology and Animal Nutrition 101(3):576–588
DOI 10.1111/jpn.12461.
Albiker D, Zweifel R. 2019. Pflanzenkohle im Futter oder in der Einstreu und ihre Wirkung auf die
Stickstoffretention und Leistung von Broilern. In: Wissenschaftstagung Ökologischer Landbau.
Vol. 15. Kassel: Stiftung Ökologie & Landbau, 276–283.
Alshannaq A, Yu J-H. 2017. Occurrence, toxicity, and analysis of major mycotoxins in food.
International Journal of Environmental Research and Public Health 14(6):632
DOI 10.3390/ijerph14060632.
Anca-Couce A, Mehrabian R, Scharler R, Obernberger I. 2014. Kinetic scheme of biomass
pyrolysis considering secondary charring reactions. Energy Conversion and Management
87:687–696 DOI 10.1016/j.enconman.2014.07.061.
Anderson PS, Reed TB, Wever PW. 2007. Micro-gasification: what it is and why it works.
Boiling Point 53:35–37.
Avantaggiato G, Havenaar R, Visconti A. 2004. Evaluation of the intestinal absorption of
deoxynivalenol and nivalenol by an in vitro gastrointestinal model, and the binding efficacy of
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 38/54
activated carbon and other adsorbent materials. Food and Chemical Toxicology 42(5):817–824
DOI 10.1016/j.fct.2004.01.004.
Avantaggiato G, Solfrizzo M, Visconti A. 2005. Recent advances on the use of adsorbent materials
for detoxification of Fusarium mycotoxins.Food Additives and Contaminants 22(4):379–388
DOI 10.1080/02652030500058312.
Ayanwale BA, Lanko AG, Kudu YS. 2006. Performance and egg quality characteristics of
pullets fed activated sheabutter charcoal based diets. International Journal of Poultry Science
5(10):927–931 DOI 10.3923/ijps.2006.927.931.
Bakr BEA. 2007. The effect of using citrus wood charcoal in broiler rations on the performance of
broilers. An-Najah University Journal for Research 22:17–24.
Banner RE, Rogosic J, Burritt EA, Provenza FD. 2000. Supplemental barley and charcoal
increase intake of sagebrush by lambs. Journal of Range Management 53(4):415–420
DOI 10.2307/4003753.
Bannert A, Bogen C, Esperschütz J, Koubová A, Buegger F, Fischer D, Radl V, Fuß R,
Chroňáková A, Elhottová D, Šimek M, Schloter M. 2012. Anaerobic oxidation of methane
in grassland soils used for cattle husbandry. Biogeosciences 9(10):3891–3899
DOI 10.5194/bg-9-3891-2012.
Besnier P. 2014. Composition à base de Nekka-Rich pour la prévention de pathologies intestinales.
Available at http://www.google.com/patents/EP2687221A1?cl=en17 (accessed 20 February 2019).
Bhatta R, Saravanan M, Baruah L, Sampath KT. 2012. Nutrient content, in vitro ruminal
fermentation characteristics and methane reduction potential of tropical tannin-containing
leaves. Journal of the Science of Food and Agriculture 92(15):2929–2935 DOI 10.1002/jsfa.5703.
Bhatti SA, Khan MZ, Hassan ZU, Saleemi MK, Saqib M, Khatoon A, Akhter M. 2018.
Comparative efficacy of bentonite clay, activated charcoal and Trichosporon mycotoxinivorans in
regulating the feed-to-tissue transfer of mycotoxins. Journal of the Science of Food and
Agriculture 98(3):884–890 DOI 10.1002/jsfa.8533.
Borchard N, Schirrmann M, Cayuela ML, Kammann C, Wrage-Mönnig N, Estavillo JM,
Fuertes-Mendizábal T, Sigua G, Spokas K, Ippolito JA, Novak J. 2019. Biochar, soil and
land-use interactions that reduce nitrate leaching and N
2
O emissions: a meta-analysis. Science of
the Total Environment 651:2354–2364 DOI 10.1016/j.scitotenv.2018.10.060.
Bovšková H, Míková K, Panovská Z. 2014. Evaluation of egg yolk colour. Czech Journal of
Food Science 3:213–217.
Brennan RB, Healy MG, Fenton O, Lanigan GJ. 2015. The effect of chemical amendments
used for phosphorus abatement on greenhouse gas and ammonia emissions from dairy
cattle slurry: synergies and pollution swapping. PLOS ONE 10(6):e0111965
DOI 10.1371/journal.pone.0111965.
Brewer CE, Chuang VJ, Masiello CA, Gonnermann H, Gao X, Dugan B, Driver LE,
Panzacchi P, Zygourakis K, Davies C. 2014. New approaches to measuring biochar density and
porosity. Biomass and Bioenergy 66:176–185 DOI 10.1016/j.biombioe.2014.03.059.
Bucheli TD, Hilber I, Schmidt H-P. 2015. Polycyclic aromatic hydrocarbons and polychlorinated
aromatic compounds in biochar. In: Lehmann J, Joseph S, eds. Biochar for Environmental
Management. London: Routledge, 595–624.
Bueno DJ, Di Marco L, Oliver G, Bardón A. 2005. In Vitro binding of zearalenone to different
adsorbents. Journal of Food Protection 68(3):613–615 DOI 10.4315/0362-028X-68.3.613.
Cabeza I, Waterhouse T, Sohi S, Rooke JA. 2018. Effect of biochar produced from different
biomass sources and at different process temperatures on methane production and ammonia
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 39/54
concentrations in vitro. Animal Feed Science and Technology 237:1–7
DOI 10.1016/j.anifeedsci.2018.01.003.
Cai KZ, Jiang ST, He YJ. 2011. Effects of bamboo charcoal including vinegar liquid on growth
performance and meat quality in Chinese indigenous breed during fattening. Journal of Animal
and Veterinary Advances 10(18):2470–2473 DOI 10.3923/javaa.2011.2470.2473.
Calvelo Pereira R, Muetzel S, Camps Arbestain M, Bishop P, Hina K, Hedley M. 2014.
Assessment of the influence of biochar on rumen and silage fermentation: a laboratory-scale
experiment. Animal Feed Science and Technology 196:22–31 DOI 10.1016/j.anifeedsci.2014.06.019.
Cato MP. 1935. On agriculture. Cambridge: Harvard University Press.
Cederlund H, Börjesson E, Stenström J. 2017. Effects of a wood-based biochar on the leaching of
pesticides chlorpyrifos, diuron, glyphosate and MCPA. Journal of Environmental Management
191:28–34 DOI 10.1016/j.jenvman.2017.01.004.
Chen P, McCreery RL. 1996. Control of electron transfer kinetics at glassy carbon
electrodes by specific surface modification. Analytical Chemistry 68(22):3958–3965
DOI 10.1021/ac960492r.
Chen S, Rotaru A-E, Shrestha PM, Malvankar NS, Liu F, Fan W, Nevin KP, Lovley DR. 2015.
Promoting interspecies electron transfer with biochar. Scientific Reports 4(1):143
DOI 10.1038/srep05019.
Cheng C-H, Lehmann J. 2009. Ageing of black carbon along a temperature gradient. Chemosphere
75(8):1021–1027 DOI 10.1016/j.chemosphere.2009.01.045.
Choi J-S, Jung D-S, Lee J-H, Choi Y-I, Lee J-J. 2012. Growth performance, immune response and
carcass characteristics of finishing pigs by feeding stevia and charcoal. Korean Journal for
Food Science of Animal Resources 32(2):228–233 DOI 10.5851/kosfa.2012.32.2.228.
Choi JY, Shinde PL, Kwon IK, Song YH, Chae BJ. 2009. Effect of wood vinegar on the
performance, nutrient digestibility and intestinal microflora in weanling pigs. Asian-
Australasian Journal of Animal Sciences 22(2):267–274 DOI 10.5713/ajas.2009.80355.
Chu GM, Jung CK, Kim HY, Ha JH, Kim JH, Jung MS, Lee SJ, Song Y, Ibrahim RIH, Cho JH,
Lee SS, Song YM. 2013a. Effects of bamboo charcoal and bamboo vinegar as antibiotic
alternatives on growth performance, immune responses and fecal microflora population in
fattening pigs. Animal Science Journal 84:113–120 DOI 10.1111/j.1740-0929.2012.01045.x.
Chu GM, Kim JH, Kang SN, Song YM. 2013b. Effects of dietary bamboo charcoal on the carcass
characteristics and meat quality of fattening pigs. Korean Journal for Food Science of Animal
Resources 33(3):348–355 DOI 10.5851/kosfa.2013.33.3.348.
Chu GM, Kim JH, Kim HY, Ha JH, Jung MS, Song Y, Cho JH, Lee SJ, Ibrahim RIH, Lee SS,
Song YM. 2013c. Effects of bamboo charcoal on the growth performance, blood characteristics
and noxious gas emission in fattening pigs. Journal of Applied Animal Research 41(1):48–55
DOI 10.1080/09712119.2012.738219.
Clark KJ, Sarr AB, Grant PG, Phillips TD, Woode GN. 1998. In vitro studies on the use of
clay, clay minerals and charcoal to adsorb bovine rotavirus and bovine coronavirus.
Veterinary Microbiology 63(2–4):137–146 DOI 10.1016/S0378-1135(98)00241-7.
Conte P, Marsala V, De Pasquale C, Bubici S, Valagussa M, Pozzi A, Alonzo G. 2013.
Nature of water-biochar interface interactions. GCB Bioenergy 5(2):116–121
DOI 10.1111/gcbb.12009.
Cooney DO, Roach M. 1979. Sucrose as a sweetener for activated charcoal. American Journal of
Hospital Pharmacy 36(6):797–798 DOI 10.1093/ajhp/36.6.797.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 40/54
Cooney DO, Struhsaker TT. 1997. Adsorptive capacity of charcoals eaten by Zanzibar red colobus
monkeys: implications for reducing dietary toxins. International Journal of Primatology
18(2):235–246 DOI 10.1023/A:1026324703410.
Cord-Ruwisch R, Seitz H-J, Conrad R. 1988. The capacity of hydrogenotrophic anaerobic bacteria
to compete for traces of hydrogen depends on the redox potential of the terminal electron
acceptor. Archives of Microbiology 149(4):350–357 DOI 10.1007/BF00411655.
Crome P, Dawling S, Braithwaite RA, Masters J, Walkey R. 1977. Effect of activated
charcoal on absorption of nortriptyline. Lancet 310(8050):1203–1205
DOI 10.1016/S0140-6736(77)90440-8.
Dalvi RR, Ademoyero AA. 1984. Toxic effects of aflatoxin B1 in chickens given feed contaminated
with Aspergillus flavus and reduction of the toxicity by activated charcoal and some chemical
agents. Avian Diseases 28(1):61–69 DOI 10.2307/1590128.
Dalvi RR, McGowan C. 1984. Experimental induction of chronic aflatoxicosis in chickens by
purified aflatoxin B1 and its reversal by activated charcoal, phenobarbital, and reduced
glutathione. Poultry Science 63(3):485–491 DOI 10.3382/ps.0630485.
Davidson EA, Chorover J, Dail DB. 2003. A mechanism of abiotic immobilization of nitrate
in forest ecosystems: the ferrous wheel hypothesis. Global Change Biology 9(2):228–236
DOI 10.1046/j.1365-2486.2003.00592.x.
Dawling S, Crome P, Braithwaite R. 1978. Effect of delayed administration of activated
charcoal on nortriptyline absorption. European Journal of Clinical Pharmacology 14(6):445–447
DOI 10.1007/BF00716388.
Day GE. 1906. Swine: a book for students and farmers. Sherburne: Kenyon Pre.
De Mil T, Devreese M, Maes A, De Saeger S, De Backer P, Croubels S. 2017. Influence of
mycotoxin binders on the oral bioavailability of tylosin, doxycycline, diclazuril, and salinomycin
in fed broiler chickens. Poultry Science 96(7):2137–2144 DOI 10.3382/ps/pew503.
Decker WJ, Corby DG. 1971. Activated charcoal as a gastrointestinal decontaminant. Experiences
with experimental animals and human subjects. Bulletin of Environmental Contamination
and Toxicology 6(2):189–192 DOI 10.1007/BF01540104.
Denli M, Okan F. 2007. Efficacy of different adsorbents in reducing the toxic effects of
aflatoxin B1 in broiler diets. South African Journal of Animal Science 36:222–228
DOI 10.4314/sajas.v36i4.4009.
Derlet RW, Albertson TE. 1986. Activated charcoal—Past, present and future. Western Journal of
Medicine 145(4):492–496.
Deutzmann JS, Stief P, Brandes J, Schink B. 2014. Anaerobic methane oxidation coupled
to denitrification is the dominant methane sink in a deep lake. Proceedings of the National
Academy of Sciences of the United States of America 111(51):18273–18278
DOI 10.1073/pnas.1411617111.
Devreese M, Antonissen G, De Backer P, Croubels S, Devreese M, Antonissen G, De Backer P,
Croubels S. 2014. Efficacy of active carbon towards the absorption of deoxynivalenol in pigs.
Toxins 6(10):2998–3004 DOI 10.3390/toxins6102998.
Devreese M, Osselaere A, Goossens J, Vandenbroucke V, De Baere S, Eeckhout M, De Backer P,
Croubels S. 2012. New bolus models for in vivo efficacy testing of mycotoxin-detoxifying
agents in relation to EFSA guidelines, assessed using deoxynivalenol in broiler chickens.
Food Additives & Contaminants: Part A 29(7):1101–1107 DOI 10.1080/19440049.2012.671788.
Di Natale F, Gallo M, Nigro R. 2009. Adsorbents selection for aflatoxins removal in bovine milks.
Journal of Food Engineering 95(1):186–191 DOI 10.1016/j.jfoodeng.2009.04.023.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 41/54
Diaz DE, Hagler WM Jr, Blackwelder JT, Eve JA, Hopkins BA, Anderson KL, Jones FT,
Whitlow LW. 2004. Aflatoxin binders II: reduction of aflatoxin M1 in milk by sequestering
agents of cows consuming aflatoxin in feed. Mycopathologia 157(2):233–241
DOI 10.1023/B:MYCO.0000020587.93872.59.
Diaz DE, Hagler WM Jr, Hopkins BA, Whitlow LW. 2002. Aflatoxin binders I: in vitro binding
assay for aflatoxin B1 by several potential sequestering agents. Mycopathologia 156(3):223–226
DOI 10.1023/A:1023388321713.
Diez-Gonzalez F, Callaway TR, Kizoulis MG, Russel JB. 1998. Grain feeding and the
dissemination of acid-resistant Escherichia coli from cattle. Science 281(5383):1666–1668
DOI 10.1126/science.281.5383.1666.
Dobson RC, Fahey JE, Ballee DL, Baugh ER. 1971. Reduction of chlorinated hydrocarbon
residue in swine. Bulletin of Environmental Contamination and Toxicology 6(2):189–192
DOI 10.1007/BF01540104.
Döll S, Dänicke S, Valenta H, Flachowsky G. 2007. In vitro studies on the evaluation of mycotoxin
detoxifying agents for their efficacy on deoxynivalenol and zearalenone. Archives of Animal
Nutrition 58:311–324.
Edmunds JL, Worgan HJ, Dougal K, Girdwood SE, Dougls J-L, McEwan NR. 2016. In vitro
analysis of the effect of supplementation with activated charcoal on the equine hindgut.
Journal of Equine Science 27(2):49–55 DOI 10.1294/jes.27.49.
Edrington T, Kubena L, Harvey R, Rottinghaus G. 1997. Influence of a superactivated charcoal
on the toxic effects of aflatoxin or T-2 toxin in growing broilers. Poultry Science 76(9):1205–1211
DOI 10.1093/ps/76.9.1205.
Edrington TS, Sarr AB, Kubena LF, Harvey RB, Phillips TD. 1996. Hydrated sodium calcium
aluminosilicate (HSCAS), acidic HSCAS, and activated charcoal reduce urinary excretion of
aflatoxin M1 in turkey poults. Lack of effect by activated charcoal on aflatoxicosis. Toxicology
Letters 89(2):115–122 DOI 10.1016/S0378-4274(96)03795-2.
Erb F, Gairin D, Leroux N. 1989. Activated charcoals: properties-experimental studies. Journal de
Toxicologie Clinique et Expérimentale 9:235–248.
Erickson PS, Whitehouse NL, Dunn ML. 2011. Activated carbon supplementation of dairy cow
diets: effects on apparent total-tract nutrient digestibility and taste preference. Professional
Animal Scientist 27(5):428–434 DOI 10.15232/S1080-7446(15)30515-5.
European Biochar Foundation (EBC). 2012. European biochar certificate—guidelines for a
sustainable production of biochar. Version 8.2 of 19th April 2019. Available at
http://www.european-biochar.org/en/download (accessed 12 January 2016).
European Biochar Foundation (EBC). 2013. EBC certified producers. Available at http://www.
european-biochar.org/en/producer (accessed 30 March 2018).
European Biochar Foundation (EBC). 2018. Guidelines for EBC-feed certification. Available at
http://www.european-biochar.org/biochar/media/doc/ebc-feed.pdf (accessed 4 January 2019).
Evans AM, Boney JW, Moritz JS. 2016. The effect of poultry litter biochar on pellet quality, one to
21 d broiler performance, digesta viscosity, bone mineralization, and apparent ileal amino acid
digestibility. Journal of Applied Poultry Research 26(1):89–98 DOI 10.3382/japr/pfw049.
Fanchiotti FE, De Moraes GHK, De Barbosa AA, Albino LFT, Cecon PR, De Moura AMA.
2010. Avaliação de óleos, carvão vegetal e vitamina E no desempenho e nas concentrações
lipídicas do sangue e dos ovos de poedeiras. Revista Brasileira de Zootecnia 39(12):2676–2682
DOI 10.1590/S1516-35982010001200017.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 42/54
Foster TS, Morley HV, Purkayastha R, Greenhalgh R, Hunt JR. 1972. Residues in eggs and
tissues of hens fed a ration containing low levels of pesticides with and without charcoal.
Journal of Economic Entomology 65(4):982–988 DOI 10.1093/jee/65.4.982.
Fries GF, Marrow GS Jr, Gordon CH, Dryden LP, Hartman AM. 1970. Effect of activated carbon
on elimination of organochlorine pesticides from rats and cows. Journal of Dairy Science
53(11):1632–1637 DOI 10.3168/jds.S0022-0302(70)86449-9.
Fujita H, Honda K, Iwakiri R, Guruge KS, Yamanaka N, Tanimura N. 2012. Suppressive effect
of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and dioxin-like
polychlorinated biphenyls transfer from feed to eggs of laying hens by activated carbon as feed
additive. Chemosphere 88(7):820–827 DOI 10.1016/j.chemosphere.2012.03.088.
Galvano F, Pietri A, Bertuzzi T, Fusconi G, Galvano M, Piva A, Piva G. 1996b. Reduction of
carryover of aflatoxin from cow feed to milk by addition of activated carbons. Journal of
Food Protection 59(5):551–554 DOI 10.4315/0362-028X-59.5.551.
Galvano F, Pietri A, Fallico B, Bertuzzi T, Scirè S, Galvano M, Maggiore R. 1996a. Activated
carbons: in vitro affinity for aflatoxin B1 and relation of adsorption ability to physicochemical
parameters. Journal of Food Protection 59(5):545–550 DOI 10.4315/0362-028X-59.5.545.
Gerlach H, Gerlach A, Schrödl W, Schottdorf B, Haufe S, Helm H, Shehata A, Krüger M. 2014.
Oral application of charcoal and humic acids to dairy cows influences Clostridium botulinum
blood serum antibody level and glyphosate excretion in urine. Journal of Clinical Toxicology
4(2):186 DOI 10.4172/2161-0495.1000186.
Gerlach A, Schmidt HP. 2012. Pflanzenkohle in der Rinderhaltung. Ithaka Journal 1:80–84.
Godlewska P, Schmidt HP, Ok YS, Oleszczuk P. 2017. Biochar for composting improvement
and contaminants reduction. A review. Bioresource Technology 246:193–202
DOI 10.1016/j.biortech.2017.07.095.
Gregory KB, Bond DR, Lovley DR. 2004. Graphite electrodes as electron donors for anaerobic
respiration. Environmental Microbiology 6(6):596–604 DOI 10.1111/j.1462-2920.2004.00593.x.
Gaudreault P, Friedman PA, Lovejoy FH Jr. 1985. Efficacy of activated charcoal and
magnesium citrate in the treatment of oral paraquat intoxication. Annals of Emergency Medicine
14(2):123–125 DOI 10.1016/S0196-0644(85)81072-6.
Gurtler JB, Boateng AA, Han YH, Douds DD Jr. 2014. Inactivation of E. coli O157: H7 in
cultivable soil by fast and slow pyrolysis-generated biochar. Foodborne Pathogens and Disease
11(3):215–223 DOI 10.1089/fpd.2013.1631.
Hagemann N, Joseph S, Schmidt H, Kammann CI, Harter J, Borch T, Young RB, Varga K,
Taherymoosavi S, Elliott KW, Albu M, Mayrhofer C, Obst M, Conte P, Dieguez A, Orsetti S,
Subdiaga E, Behrens S, Kappler A, Nutrition P, Sciences C. 2017. Organic coating on
biochar explains its nutrient retention and stimulation of soil fertility. Nature Communications
8(1):163 DOI 10.1038/s41467-017-01123-0.
Hagemann N, Spokas K, Schmidt H-P, Kägi R, Böhler MA, Bucheli T. 2018. Activated carbon,
biochar and charcoal: linkages and synergies across pyrogenic carbon’s ABCs. Water 10(2):182
DOI 10.3390/w10020182.
Hall KE, Spokas KA, Gamiz B, Cox L, Papiernik SK, Koskinen WC. 2018. Glyphosate
sorption/desorption on biochars—interactions of physical and chemical processes.
Pest Management Science 74(5):1206–1212 DOI 10.1002/ps.4530.
Hansen HH, Storm IMLD, Sell AM. 2012. Effect of biochar on in vitro rumen methane
production. Acta Agriculturae Scandinavica, Section A—Animal Science 62(4):305–309
DOI 10.1080/09064702.2013.789548.
Schmidt et al. (2019), PeerJ, DOI 10.7717/peerj.7373 43/54