The relevance of feed diversity and choice in nutrition of ruminant livestock

Abstract

In this position paper, we argue that the realisation of forage diversity and feed choice for ruminant livestock should be considered as an essential aspect of animal welfare because selection from an array of different plants is an important experience for such animals. We provide examples that diet balancing with regard to nutrients and plant secondary metabolites is particularly for ruminants so much essential that this ability must be a deeply rooted cognitive and behavioural predisposition. In this context, we assume feed choice to be a behavioural need of ruminants. Therefore, we argue in favour of nutritional concepts, which account for botanical and biochemical diversity and are based on behavioural research approaches. We provide a brief outlook of potential research topics, which we consider important if the societal target of animal welfare is to be reached in European ruminant production systems.

Full text

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Leiber et al. (2020) · LANDBAUFORSCH · J Sustainable Organic Ag ric Syst · 70(1):35–38
DOI:10.32 20/LBF1592393539000
POSITION PAPER
The relevance of feed diversity and choice
in nutrition of ruminant livestock
Florian Leiber1, Michael Walkenhorst
1, Mirjam Holinger1
1 Research Institute of Organic Agriculture (FiBL), Switzerland
CONTACT: orian.leiber@bl.org
In this position paper, we argue that the realisation of forage
diversity and feed choice for ruminant livestock should be
considered as an essential aspect of animal welfare because
selection from an array of dierent plants is an important
experience for such animals.
We provide examples that
diet balancing with regard to nutrients and plant secondary
metabolites is particularly for ruminants so much essen-
tial that this ability must be a deeply rooted cognitive and
behaviour al predisposition. In this context, we assume feed
choice to be a behavioural need of ruminants. Therefore, we
argue in favour of nutritional concepts, which account for
botanical and bioche mical diversity and are based on behav-
ioural research approaches.
We provide a brief outlook of
potential research topics, which we consider important
if the societal target of animal welfare is to be reached in
European ruminant production systems.
1 Feeding as part of animal welfare
Animal welfare cannot be dened only by the absence of dis-
tress like fear, pain, hunger, and disease; it also must include
the presence of certain stimuli, including eustress (Vil lalba
and Manteca, 2019), and the opportunity to express key
species-specic behaviour (Fraser et al., 2013). The latter is
realised in many livestock systems to a very limited degree
or not at all. Degrees of freedom in social and reproductive
behaviour are extremely low, as is the range of movement
and the opportunity to explore the environment compared
to situations in wildlife for the same species. A further aspect
of behaviour, which appears to be underestimated in its
meaning to animals in agriculture, is feed selection, includ-
ing the experience of taste, smell, exploration, and choice.
Using ruminants as an example,
the presented position pap er
argues that feed choice could be a
f
undamental physiological
and behavioural need of herbivores.
Therefore, neglecting
it in contemporary feeding schemes would imply a serious
violation of welfare.
2 Biological background
In their natural feeding behaviour, animals do not primarily
optimise the ratio of spent over gained energy. T
hey often
rather prefer to explore and to search for less easily ac ces-
sible feed (Inglis et al., 1997), select not only nutrients but
also bioactive plant compounds (Villalba et al., 2010), and
thereby maintain diurnal rhythms (Rutter, 2010) and
bal-
ance metabolic processes (Villalba et al., 2010). There appear
to be several evolutionary reasons for the development of
such behaviour. For herbivores, the balancing of their diets
by combining feed plants with dierent nutrient proles is
essential for digestive eciency and metabolic health.
Since
these nutrient proles change with phenologi cal stage, the
animals have to be able to adapt their be haviour continu-
ously (Westoby, 1978). However, the
challenge is not only
Received: September 23, 2019
Revised: D ecember 15, 2019
Accepted: Januar y 23, 2020
KEYWORDS animal welfare, grazing, ruminant physiology,
pasture biodiversity, forage selection
Florian Leiber Michael Walkenhorst Mirjam Holinger
© Cornelia Kögler
© Andi Basler
© Andi Basler

36 Leiber et al. (2020) · LANDBAUFORSCH · J Sustainable O rganic Agric Syst · 70(1):35–38
to balance nutrients like proteins and carbohydrates. Her-
bivores also have to avoid or select potential toxins in cer-
tain situations, e.g. when they are needed in low dosages in
order to control diseases or metabolic processes (Villalba et
al., 2010; Poli et al., 2018). For ruminant livestock, this has also
a veterinary aspect (Walkenhorst et al., 2020).
Diet balancing (Westoby, 1978) and targeted selection
for or against specic secondary plant metabolites have a
further dimension in ruminants: control of the foregut fer-
mentation process. The rumen microbiome is sensible to diet
char acter istics regarding degradability of carbohydrates as
well as energy to protein balances (Snelling et al., 2019), but
also concerning bioacti ve compounds such as sap onins (Goel
et al., 2008) and polyphenols (Vasta et al., 2019). Balance of
nutrients (including their ruminal degradability) is impo rtant
in order to avoid inecient utilisation of protein or energy
but also to prevent collapse of the rumen, for instance, by
rumen acidosis or bloat. However, there are also other dier-
en tiated balances, which the ruminant has to maintain in
the foregut, for instance in order to protect essential plant
metabolites from ruminal degradation.
One illustrious ex am-
ple is linolenic acid, which is the only relevant source of ome-
ga- 3 fatty acid conguration for herbivores.
More than 95 % of
ingested linolenic acid, which is essential for many functions
in the mammal organism (Sinclair et al., 2002), may be lost by
derivatisation in the rumen (Chilliard et al., 2007). Given this
example, it is our hypothesis that a foregut-fermenting spe-
cies must by all means ensure that the microbiome in their
stomach is balanced so that not too much of essential plant
nutrients are degraded or modied and lost. One eective
instrument for the animal to control the rumen microora
are bioactive secondary plant compounds (e.g. essential oils,
phenols, alkaloids) with antimicrobial properties ( Vasta et al.,
2019). Experimental evidence shows that dietary secondary
plant compounds can protect linolenic acid in the rumen
(Vasta et al., 2019), which results in increased linolenic acid
concentrations in milk (Kälber et al., 2011), muscle and adi-
pose tissue (Willems et al., 2014). The case of linolenic acid is
an example that shows the importance of rumen control by
nely dosed ingestion of secondary plant metabolites. We
hypothesize that this requires a highly dierentiated feed
selection ability of the ruminant. The concept of nutrient
bal ancing (Westoby, 1978) must therefore take into account
these substances, also considering the trade-o with fermen-
tation eciency in the rumen, which makes the task for the
(wild) ruminant even more challenging.
3 Does feed choice have an emotional
implication?
Nutrients, as well as secondar y plant metabolites, possess
odour and taste properties, such as sweet, bitter, astringent,
or sharp but also specic ally aromatic (Wichtl, 2009). A neuro-
nal relation between metabolic needs for (or excess of) cer-
tain substances and the odour and taste experience is there-
fore strongly developed in ruminants (Ginane et al., 2011). A
sensory feedback, based on genetic determination (Clauss
et al., 2010), epigenetic eects (Wiedmeier et al., 2012), and
individual experience (Villalba and Manteca, 2019) inuences
dosed selection or refusal of nutrients and bioactive plant
compounds ingested from the natural forage environment
in which ruminants have evolved. We should consider that
the ability to translate metabolic needs into avour-guided
dierentiation of herbal biomass must be deeply rooted
in the ruminants’ behaviour because it is a precondition of
their survival and evolution. This ability is expressed in vari-
ous examples of self-medication in ruminants (Villalba et al.,
2010; Poli et al., 2018). A further aspect of selective eating
behaviour is diurnal alteration in preferences as described
by Rutter (2010), who found that ruminants decrease their
preference for protein-rich forage during the course of the
day. Another study demonstrated high sensibility of the di ur-
nal eating and rumination rhythm of dairy cows to even small
changes in monotonous mixed rations (Leiber et al., 2015). It
seems likely that ruminants are able and show a behavioural
need to inuence their “gut feeling” in accordance with their
sensory fee dback by actively choosing not only the composi-
tion but also time, duration, and amount of intake.
Diet selection by ruminants has thus at least three inter-
related levels of implication: (i) the physiological need for
selection, (ii) the translational processes, which connect
physiological needs with sensorial experience and action,
and (iii) the emotional importance for the animal to display a
dierentiated explorative behaviour in challenging environ-
ments (reviewed by Villalba and Manteca, 2019). We consider
the emotional level of behavioural experience to be pos sibly
so much important that the deprivation from feed selec-
tion may have a highly negative impact, even if all nutrients
and phytochemicals are provided in a perfect diet.
If animal
nutrition does only account for the molecular composition
of diets in order to elevate nutrient eciency
to the max,
we must assume that the better the nutritionists work, the
worse it will be for the animal as a b eing which needs to have
varying sensorial experience. Scientists, which have worked
on selection behaviour of ruminants, have clearly stated the
possibility of frus tration and poor welfare if feed choice is not
possible (Rutter, 2010; Villalba et al., 2010). This implies that
the standardisation of feed rations for ruminants, commonly
used in most European dairy production systems, including
organic, impairs welfare and neglects
the principle of en a-
bling
species-specic behaviour in livestock husbandry in a
rather severe way.
4
A paradigm-shift for ruminant
nutrition
concepts
“Even after thousands of years of domestication, livestock
appear to retain at least some of the survival traits that
evolved in their ancestors. Rather than ignore these evolu-
tionary traits, we should endeavour to consider them when
designing livestock management systems” (Rutter, 2010).
In the light of the above-mentioned considerations, a
paradigm shift in agricultural ruminant nutrition is needed
with the primary intention to include the animals’ feeding
behaviour as an integrative aspect into the concepts for live-
stock nutrition. The discussion on whether it must become

37
Leiber et al. (2020) · LANDBAUFORSCH · J Sustainable Organic Ag ric Syst · 70(1):35–38
high-performance
strategies with cattle. Returning to more
natural feeding systems would consequently also include
changes in breeding goals towards genotypes better adapt-
ed to regionally available resources (Bieber et al., 2019).
5 Conclusion
There is evidence that feed selection behaviour has such
high importance for the cognitive well-being of ruminants
that access to feed diversity should be a compulsory cri-
teri on of welfare
. Under this paradigm, always feeding total
mixed rations would be no longer acceptable, and new
feeding
concepts that take into account diversity of fe eds are
required. It appears that a more natural feeding concept for
ruminants can result in several positive eects. Besides the
animal welfare and health aspect of more diverse feed and
natural feeding, the suggested approach could also result in
higher biodiversity of pastures and feed crops, as a positive
side-eect.
Last but not least, product quality also in creases
when
ruminants receive diverse types of forage with high
proportions of herbs. We must therefore pay more attention
to these aspects, in practice, in research, and in standards, in
particular in the context of organic agriculture.
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