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The benefits of tannin-containing forages

The Benefits of Tannin-Containing Forages
Jennifer W. MacAdam, Dept. of Plants, Soils and Climate, Utah State University
Joe Brummer, Dept. of Soil and Crop Sciences, Colorado State University
Anowarul Islam, Dept. of Plant Sciences, University of Wyoming
Glenn Shewmaker, Dept. of Plant, Soil, and Entomological Sciences, University of Idaho
What Are Tannins?
Tannins, a group of chemical compounds pro-
duced by a number of broadleaf forage plants,
can bind proteins. Typically, grasses don’t con-
tain tannins, although sorghum (Sorghum bicol-
or) has a significant tannin content. Tannins are
often found in higher concentrations in broadleaf
plants adapted to warm climates. For example,
sericea lespedeza (Lespedeza cuneata) is a for-
age cultivated in the midwestern and southern
U.S. that can accumulate tannins to as much as
18% of herbage dry matter (Mueller-Harvey,
Because tannins bind salivary proteins, they
produce an astringent or puckery sensation in the
mouth when foods with a high tannin content
(such as unripe fruits) are eaten. Tannins are
effective in preserving (tanning) leather because
they bind to the collagen protein in animal skins,
preventing microbial breakdown. The French
word “tannin” is related to the German word
“tannenbaum” (meaning fir tree), and is derived
from an older Latin term for oak bark, which
was an early source of tannins for leather-
Proteins are needed to carry out the metabolic
activities in living cells, so the content of protein
is high in plant cells. For this reason, tannins in
plants are segregated in vacuoles, which are wa-
ter-filled structures in the center of most plant
cells, or in special compartments called tannin
sacs (Fig. 1). This segregation keeps tannins
from interfering with plant metabolism.
Figure 1. Cell sap pressed from the tannin sacs of
three sainfoin leaflets before (left) and after (right)
staining for tannins.
What Western Forage Plants
Contain Tannins?
The amount of tannin, the location of tannins in
leaves, stems or flowers, and the chemical struc-
ture of tannins vary greatly among the plants
that accumulate these compounds. Alfalfa
(Medicago sativa) can produce tannins, but they
only occur in seed coats; white clover (Trifolium
repens) produces tannins, but they only occur in
flowers. In these cases, the amount of tannin
consumed by ruminants grazing these forages is
negligible. Two forage plants that grow well in
the western United States and contain significant
tannins are birdsfoot trefoil (Lotus corniculatus)
and sainfoin (Onobrychis viciifolia, Fig. 2). Both
of these forages express tannins in their leaves.
Much of the re-
search on tannin-
containing forag-
es has been car-
ried out by ani-
mal and forage
scientists in New
Zealand, where
cattle and sheep
are raised pri-
marily on peren-
nial ryegrass
(Lolium perenne)
pastures. In an
effort to identify
forage species
capable of im-
proving ruminant
production on
pastures, many
legume and other forb species were studied and
the beneficial traits of tannin-containing forage
plant species were documented.
The tannin produced by birdsfoot trefoil has rou-
tinely been found to increase ruminant produc-
tivity, and there is evidence that the tannins pro-
duced by sainfoin and sulla (Hedysarum
coronarium) may also have positive effects on
ruminant productivity. However, the results of
studies on sainfoin and sulla are not consistently
positive (Waghorn, 2008).
What Do Forage Tannins Do?
Two general traits of tannins relevant to grazing
ruminants are the prevention of bloat (Lees,
1992) and the suppression of internal parasites
(Hoste et al., 2006). Pasture bloat occurs when a
substantial amount of fresh, high-protein forage,
such as alfalfa, is digested quickly, resulting in a
rapid increase in the protein content of the ru-
men. This causes the rate of microbial fermenta-
tion in the rumen to increase, and results in rapid
accumulation of carbon dioxide and methane
gases in the rumen. Microbial slime, plant cellu-
lar membranes and proteins all combine with
fermentation gases to create a stable foam that’s
perceived as a liquid at the valve leading from
the rumen into the esophagus, causing it to re-
main closed (Howarth et al., 1991). As the gases
trapped in the rumen continue to accumulate, the
rumen becomes distended, interfering with
breathing and blood flow. Left untreated, bloat
can result in death from suffocation or cardiac
arrest. Tannin-containing forages are non-bloat-
ing because tannins bind excess plant proteins,
precipitating them out of rumen fluid, and in the
process, preventing the creation of the stable
foam that’s characteristic of pasture bloat.
The suppression of internal parasites by tannins,
specifically the suppression of numerous nema-
tode species, has been documented for sainfoin
and birdsfoot trefoil, and for purified tannins
from woody plant species used as dietary sup-
plements (Younie et al., 2004). The effect of
tannins on nematodes depends on the tannin
concentration and chemical structure as well as
the species of nematode. The effectiveness of
tannins also differs by the stage of growth of the
nematode, and the location in the gastrointestinal
tract where the tannin is active.
How Do Tannin-Containing For-
ages Alter Forage Utilization?
Compared with grasses, legumes have less fiber
and the fiber in legumes is digested more rapidly
than the fiber in grasses (Smith et al., 1972).
Therefore, legumes are digested more quickly
than grasses, which means that intake and
productivity can be higher on legume than on
grass pastures (Crampton et al., 1960). The
problem with a diet consisting of highly digesti-
ble legume forages is that their protein content is
much higher than the dietary requirements of
ruminants, and their energy (carbohydrate) con-
tent is relatively low. In the rumen, this problem
is solved when microbes use the carbohydrate
“backbone” of proteins as energy. However, the
ammonia this creates isn’t good for the ruminant
or for the environment.
In tannin-containing forages, excess plant pro-
teins that become bound to tannins leave the ru-
men without being digested. Unfortunately, the
tannin chemistry or concentration in most forag-
es results in irreversible binding of proteins. In
these cases the protein is never digested, and
Figure 2. Sainfoin
both forage intake and digestibility are reduced
(Reed, 1995). As a result, forages such as big
trefoil (Lotus pedunculatus) can prevent bloat,
but also reduce ruminant productivity (Barry and
Duncan, 1984).
Like other tannins, those in birdsfoot trefoil (Fig.
3) bind excess plant proteins in the rumen, pre-
venting bloat. However, unlike most tannins,
they release these proteins in the abomasum in
response to low pH. This allows the protein to
be digested and absorbed in the small intestine
(Waghorn et al., 1987) and results in high
productivity in both sheep (Douglas et al., 1995)
and cattle (Wen et al., 2002). In Utah, season-
long average daily gains of 2.87 to 3.35 lbs. per
day have been achieved on birdsfoot trefoil pas-
tures (MacAdam et al., 2011).
Tannin Environmental Benefits
High-protein forages can result in high nitrogen
concentrations in both milk and urine, but when
birdsfoot trefoil is fed and excess proteins are
digested in the abomasum instead of being used
for energy in the rumen, the nitrogen concentra-
tion of milk and urine is reduced and more ni-
trogen is excreted as solid waste. This has been
shown in studies by Woodward and others
(2009) where urinary nitrogen was reduced as
birdsfoot trefoil was increased relative to peren-
nial ryegrass in dairy cow diets, and by
Misselbrook and others (2005), where ammonia
emissions from dairy manure were reduced
when cows were fed birdsfoot trefoil silage in-
stead of alfalfa silage.
The rate of nitrogen released into the soil from
the manure of sheep fed birdsfoot trefoil was
reduced compared with the manure of sheep fed
white clover (Crush and Keogh, 1998). Over
time, this would increase the rate of soil organic
matter accumulation in pastures planted with
birdsfoot trefoil. Birdsfoot trefoil tannins have
also been shown to reduce the enteric (digestive)
methane production of dairy cows compared
with cows fed perennial ryegrass (Woodward et
al., 2004).
The inclusion of highly digestible legumes such
as birdsfoot trefoil in pasture plantings can in-
crease the productivity of grazing livestock. Be-
cause forage legumes produce their own nitro-
gen as long as they’re inoculated with the proper
Rhizobium bacterium at planting, they can meet
their own nitrogen fertilization needs as well as
those of associated pasture grasses. Since
birdsfoot trefoil and other tannin-containing for-
age legumes are non-bloating, they can be plant-
ed as 50% or more of mixtures with no risk of
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... Tannins have been discovered in plants that have adapted to hot climates and have larger leaves, including Sorghum bicolor, Lespedeza cuneata, and others. Numerous tannins have been detected in a few sections of some plant species; e.g., in white clover (Trifolium repens) and seed coats of other plants (Alfalfa or Medicago sativa) [55]. Tannins can also be found in a variety of plant parts, including leaves, roots, stems, fruits, peels, seeds, shells, and bark (Table 1). ...
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Tannins are soluble, astringent secondary phenolic metabolites generally obtained from renewable natural resources, and can be found in many plant parts, such as fruits, stems, leaves, seeds, roots, buds, and tree barks, where they have a protective function against bacterial, fungal, and insect attacks. In general, tannins can be extracted using hot water or organic solvents from the bark, leaves, and stems of plants. Industrially, tannins are applied to produce adhesives, wood coatings, and other applications in the wood and polymer industries. In addition, tannins can also be used as a renewable and environmentally friendly material to manufacture bio-based polyurethanes (bio-PUs) to reduce or eliminate the toxicity of isocyanates used in their manufacture. Tannin-based bio-PUs can improve the mechanical and thermal properties of polymers used in the automotive, wood, and construction industries. The various uses of tannins need to be put into perspective with regards to possible further advances and future potential for value-added applications. Tannins are employed in a wide range of industrial applications, including the production of leather and wood adhesives, accounting for almost 90% of the global commercial tannin output. The shortage of natural resources, as well as the growing environmental concerns related to the reduction of harmful emissions of formaldehyde or isocyanates used in the production of polyurethanes, have driven the industrial and academic interest towards the development of tannin-based bio-PUs as sustainable alternative materials with satisfactory characteristics. The aim of the present review is to comprehensively summarize the current state of research in the field of development, characterization, and application of tannin-derived, bio-based polyurethane resins. The successful synthesis process of the tannin-based bio-PUs was characterized by Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), MALDI-TOF mass spectrometry, and gel permeation chromatography (GPC) analyses.
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Tannins are complex, astringent and water soluble phenolic compounds known to reduce the bioavailability of nutrients in gut. Furthermore, tannins pose some health consequences viz. antinutritional effect, reduced digestibility, mutagenic and carcinogenic effects and inducer, hepatotoxic activity and co-promoters of several diseases. However, recent studies have explored and confirmed numerous health benefits like anti-oxidant, anti-cancerous, anti-allergic, anti-inflammatory, anti-helminthic and anti-microbial activities). Owing to their astringency, the food applications are very limited; whereas, they have wide applications in pharmaceutical industries. The present review has been aimed to highlight the classification, sources, occurrence, health effects, industrial applications and the safe limits of consumption of tannins.
This book was conceived as an activity of the Network on Animal Health and Welfare in Organic Agriculture, an EU funded network of researchers from 13 countries, and most of the authors were drawn from the network. A problem identified by the authors is the diversity that occurs inevitablyin organic agriculture, as it must adapt to the local conditions. Because of this they have limited the scope of the book to organic farming in Europe. The 17 chapters cover: the principles and values of organic farming; a historical perspective of animals in agriculture; diversity in organic livestock systems; organic livestock standards; welfare and ethics; understanding animal behaviour in organic systems; applied ethology in improving welfare; mutilations (including dehorning, debeaking); assessing animal welfare; humans in managing organic herds; health and disease on organic farms; promoting health and welfare through planning; treatment of animals; grassland management and parasite control; feeding; breeding; and future challenges. In the appendix the objectives of the Network of Animal Health and Welfare in Organic Agriculture are listed with its main conclusions and recommendations on the development of standards and regulations, development of systems and training, and research needs.
Two grazing experiments were conducted to compare the productivity of lactating ewes (Experiment 1) and weaned lambs (Experiment 2) grazing swards of Lotus corniculatus (birdsfoot trefoil; cv. Grasslands Goldie), lucerne (Medicago sativa; cv. Grasslands Oranga), and a mixture of lucerne and lotus. Measurements were made of pre‐ and post‐grazing herbage mass, the composition of the feed on offer and diet selected, and of voluntary feed intake (VFI; Experiment 2 only), body growth, and wool growth. From the agronomic measurements, it was concluded that the diet selected was mainly leaf in both experiments. Total condensed tannin (CT) content was 32–57 g/kg DM for lotus, 8–10 g/kg DM for the mixture, and negligible for lucerne (less than 2 g/kg DM). In Experiment 1, ewe wool production and lamb liveweight gain (LWG) did not differ between forages, but ewe LWG was greater on lotus than on lucerne (251 versus 65 g/day; P < 0.001), with the mixture being intermediate (115 g/day). In Experiment 2, VFI (1.76 versus 1.65 kg organic matter (OM)/day; P < 0.05), LWG (228 versus 183 g/day; P < 0.001), wool production (2.78 versus 2.25 kg; P < 0.05), and carcass weight (20.4 versus 17.8 kg; P < 0.05) were greater for lambs grazing lotus than lucerne; lambs grazing the mixture had similar VFI (1.63 kg OM/day) to those grazing lucerne, but wool production (2.49 kg) was intermediate between lambs grazing lucerne and lotus. Male lambs showed a greater LWG response to lotus relative to lucerne (+83 g/day P < 0.01) than female lambs (+15 g/day; P > 0.05). When adjusted for differences in carcass weight, lotus did not affect carcass fatness (GR 13.1 versus 12.8 mm; P > 0.05). It was concluded that Lotus corniculatus (cv. Grasslands Goldie) supported high levels of sheep productivity, with the responses in wool production and superior growth of male lambs in Experiment 2 suggesting that part of the response may be the result of increased protein supply from action of CT in the digestive system.
Forage fiber digestion followed first- order reaction kinetics even though in- dividual forages differed widely in ma- turity, composition, and rate of fiber digestion. Linearity of individual semilog plots of remaining digestible cell walls on time and their individually high r z (mean ,978) for each of 112 different samples representing 15 species support this general model. Cell wall digestion rates were more highly correlated with soluble dry matter percentage (y = --.0299 -b .00261X, r =.72, P < .001) than with )ignin percentage (r = --.47, P < .001), lignin-to-cellulose (r = --.18), log lignin-to-cellulose ratio (r = --.26, P < .01), or 72 hr in vitro cell wall indigestibility (r = --.38, P < .001). Similarity of mean lignin-to-cellu- lose ratios in theoretically indigestible residues from legumes (1.09) and grasses (.94) suggests a similar role of lignin in limiting extent of digestion. Lignin in dry matter, lignin:cellulose, or log lignin:cel- lulose seem to be equally suitable pre- dictors of cell wall indigestibility in vitro. Legumes were higher in percentage soluble dry matter and lignin and lower in percentage hemicellulose than grasses. Legume cell walls were also more ligni- fied and less digestible, but digested faster than grass cell walls.
Condensed tannins (CT) have improved liveweight gain, wool production and reproductive efficiency in sheep fed temperate forages and reduced the impact of gastro-intestinal parasitism. However, their value is also linked to environmental issues, such as reducing nitrogen pollution from animals grazing lush pastures with a high nitrogen content and lessening methane emissions from rumen fermentation. When forages are fed as a sole diet, the CT in birdsfoot trefoil (Lotus corniculatus) have been beneficial for ruminant production, but the CT in sainfoin, (Onobrychis), sulla (Hedysarum coronarium) and lotus major (L. pedunculatus) do not appear to benefit productivity other than by mitigating the impact of parasites. The sainfoin, sulla and lotus major have a high feeding value, but the CT per se offer no benefits for nutrition. In contrast to temperate farming, the CT in browse, typical of warm and hot climates, are nearly always detrimental to ruminants, except for reducing internal parasite numbers. Grasses fed in these regions contain less protein (and usually more fibre) than temperate forages and inclusion of CT from browse further reduces protein availability for absorption by limiting ruminal microbial growth and lowering the fractional absorption of amino acids from the intestine. Intakes of CT from browse, in combination with a medium–poor quality diet, are detrimental to performance. However recent studies have shown inclusion of polyethylene glycol (PEG) in diets for sheep and goats grazing scrub and woodland can markedly improve performance, with as little as 10g/day. The success of research to improve the performance of animals consuming diets containing CT in both temperate and hot climates will depend on communication between animal scientists and chemists. Researchers must measure the astringency and chemical characteristics of CT (and other secondary metabolites), to better understand the impact of tanniniferous feeds on nutritive value. These measurements will enable findings from unrelated trials to be evaluated and provide opportunities for optimising and mitigating the CT in contrasting ruminant production systems.
Birdsfoot trefoil (BFT; Lotus corniculatus L.) is a tannin-containing, nonbloating forage legume that is productive and persistent under irrigation in the Mountain West region of the United States. The unique type and concentration of condensed tannins in BFT increase ruminant production. The hypothesis of this study was that the ADG of cattle grazing monoculture BFT would be greater than that of cattle grazing cicer milkvetch (CMV; Astragalus cicer L.), a nonbloating forage legume that does not contain tannins. Weaned, fall-born Tarentaise calves (mixed sex; n = 3) grazed monoculture legume pastures for 2 periods of 30 and 31 d beginning 3 June 2008 and 2 periods of 45 and 32 d beginning 3 June 2009 (steers; n = 2). Initial BW were 301 ± 15 kg and 282 ± 12 kg in 2008 and 2009, respectively. Treatments were Norcen and Oberhaunstadter BFT, previously shown to have low and medium tannin concentrations, respectively, and nontannin Monarch CMV, all similar in forage nutritive value to alfalfa (Medicago sativa L.). In 2008, ADG was greater for the medium-tannin BFT than for CMV in the first period (P = 0.07) but greater for CMV in the second period (P = 0.09). In 2009, gains were greater for both BFT cultivars than for CMV in the first period (P < 0.01) and did not differ among legume treatments in the second period. Weighted mean ADG in 2008 were 1.42, 1.35, and 1.64 kg/d for CMV, low-tannin BFT, and medium-tannin BFT, respectively, and in 2009, were 0.97, 1.25, and 1.40 kg/d for those respective legume pastures. Mean cattle blood plasma omega-6 to omega-3 fatty acid ratios ranged from 1.39 to 1.91 and were greater on BFT than CMV pastures (P < 0.01 to 0.02). Although based on limited cattle numbers, this study shows that perennial nonbloating legume pastures have the potential to produce high ADG in cattle.
This paper examines the nutritional and veterinary effects of tannins on ruminants and makes some comparisons with non-ruminants. Tannin chemistry per se is not covered and readers are referred to several excellent reviews instead: (a) Okuda T et al.Heterocycles 30:1195–1218 (1990); (b) Ferreira D and Slade D. Nat Prod Rep 19:517–541 (2002); (c) Yoshida T et al. In Studies in Natural Product Chemistry. Elsevier Science, Amsterdam, pp. 395–453 (2000); (d) Khanbabaee K and van Ree T. Nat Prod Rep 18:641–649 (2001); (e) Okuda et al.Phytochemistry 55:513–529 (2000). The effects of tannins on rumen micro-organisms are also not reviewed, as these have been addressed by others: (a) McSweeney CS et al.Anim Feed Sci Technol 91:83–93 (2001); (b) Smith AH and Mackie RI. Appl Environ Microbiol 70:1104–1115 (2004). This paper deals first with the nutritional effects of tannins in animal feeds, their qualitative and quantitative diversity, and the implications of tannin–protein complexation. It then summarises the known physiological and harmful effects and discusses the equivocal evidence of the bioavailability of tannins. Issues concerning tannin metabolism and systemic effects are also considered. Opportunities are presented on how to treat feeds with high tannin contents, and some lesser-known but successful feeding strategies are highlighted. Recent research has explored the use of tannins for preventing animal deaths from bloat, for reducing intestinal parasites and for lowering gaseous ammonia and methane emissions. Finally, several tannin assays and a hypothesis are discussed that merit further investigation in order to assess their suitability for predicting animal responses. The aim is to provoke discussion and spur readers into new approaches. An attempt is made to synthesise the emerging information for relating tannin structures with their activities. Although many plants with high levels of tannins produce negative effects and require treatments, others are very useful animal feeds. Our ability to predict whether tannin-containing feeds confer positive or negative effects will depend on interdisciplinary research between animal nutritionists and plant chemists. The elucidation of tannin structure–activity relationships presents exciting opportunities for future feeding strategies that will benefit ruminants and the environment within the contexts of extensive, semi-intensive and some intensive agricultural systems. Copyright © 2006 Society of Chemical Industry
For the past 20 years, the focus in our laboratory has been on finding the causes of ruminant pasture bloat and eventually breeding a bloat-safe alfalfa (Medicago sativa L.); i.e., with bloat potential reduced to the economic threshold. In the mid-seventies, the mechanisms of bloat were explored and found to be more physical than chemical. Characteristic of all bloating legumes after ingestion was a very rapid initial rate of ingestion by rumen microbes. Through the study of bloating and non-bloating legumes, factors were elucidated in the plant that would slow this process. One of these factors was the presence of condensed tannins in the herbage. Some of the non-bloating legumes contained these secondary metabolites, but no condensed tannins were found in any of the bloating legumes. Therefore, species containing an appreciable amount of condensed tannins in their leaves and stems are considered to be non-bloating. Conventional breeding methods have not been successful in producing an alfalfa with condensed tannins in its herbage. New approaches using tissue culture techniques are being attempted, but genetic engineering has the greatest potential for success.