Sustainability of ruminant agriculture in the new context: feeding strategies and features of animal adaptability into the necessary holistic approach

Abstract

There are numerous recent studies highlighting sustainability problems for the development of ruminant production systems (RPS) while facing increasing human food necessities and global climate change. Despite the complexity of the context, in our view the main objectives of the ruminants' physiologist should be convergent for both industrialized (IC) and developing countries (DC) in a common and global strategy of advancing knowledge. In DC, this means improving the efficiency of RPS, taking into account the unique possibility of using rangelands. For IC settings, RPS should be revisited in terms of autonomy and environment- friendly feeding and managing practices. Assuming that competition for feed/food use is still a crucial criterion, future ruminant feeding systems (FeSyst) should preferably focus on lignocellulosic sources. According to biome distributions, and the recent increases in volumes of crop residues and their by-products, the annually renewed volumes of these biomasses are considerable. Therefore, we need to redesign our strategies for their efficient utilization at the local level. For this purpose, digestion processes and rumen functioning need to be better understood. The renewed vision of ruminal digestion through the reduction of greenhouse gas emissions is also a key aspect as it is an environmental demand that cannot be ignored. With regard to other ruminants' physiological functions, accumulated knowledge could be mobilized into an integrative approach that puts forward the adaptive capacities of animals to face variability in quantity and quality of supplied feeds. Basically, the reduction of inputs that were traditionally used to ensure FeSyst will need more flexible animals. In that sense, the concepts of homeostasis and teleophorhesis need to be updated and adapted to domestic species and breeds that were until now largely excluded from the dominant productive systems. In conclusion, a more holistic approach of research targets is required in which physiological functions and farmers' practices must converge and respond to each particular situation in an integral, dynamic and flexible conceptual perspective. From a scientific point of view, both for ICs and DCs, a broader range of experimental scenarios should be explored in order to arrive at innovative practices and solutions that respect environmental, ethical and economical issues. The clear challenge is to in evaluate the sustainability of RPSs. This includes, in our opinion, a strong interaction with other disciplines (multi- and trans-disciplinary conception), thus structuring new relevant indicators for the evaluation sustainability.

Full text

Animal
(2010), 4:7, pp 1258–1273 &The Animal Consortium 2010
doi:10.1017/S1751731110001023
animal
Sustainability of ruminant agriculture in the new context:
feeding strategies and features of animal adaptability
into the necessary holistic approach
F. Bocquier
1
-
and E. Gonza
´lez-Garcı
´a
2
1
Montpellier SupAgro, UMR868 ERRC, Ba
ˆtiment 22, Campus SupAgro-INRA, 2 Place Pierre Viala, F-34060 Montpellier, France;
2
INRA, UMR868 ERRC,
F-34060 Montpellier, France
(Received 6 October 2009; Accepted 9 March 2010)
There are numerous recent studies highlighting sustainability problems for the development of ruminant production systems (RPS)
while facing increasing human food necessities and global climate change. Despite the complexity of the context, in our view the
main objectives of the ruminants’ physiologist should be convergent for both industrialized (IC) and developing countries (DC) in
a common and global strategy of advancing knowledge. In DC, this means improving the efficiency of RPS, taking into account the
unique possibility of using rangelands. For IC settings, RPS should be revisited in terms of autonomy and environment- friendly
feeding and managing practices. Assuming that competition for feed/food use is still a crucial criterion, future ruminant feeding
systems (FeSyst) should preferably focus on lignocellulosic sources. According to biome distributions, and the recent increases in
volumes of crop residues and their by-products, the annually renewed volumes of these biomasses are considerable. Therefore,
we need to redesign our strategies for their efficient utilization at the local level. For this purpose, digestion processes and rumen
functioning need to be better understood. The renewed vision of ruminal digestion through the reduction of greenhouse gas
emissions is also a key aspect as it is an environmental demand that cannot be ignored. With regard to other ruminants’
physiological functions, accumulated knowledge could be mobilized into an integrative approach that puts forward the adaptive
capacities of animals to face variability in quantity and quality of supplied feeds. Basically, the reduction of inputs that were
traditionally used to ensure FeSyst will need more flexible animals. In that sense, the concepts of homeostasis and teleophorhesis
need to be updated and adapted to domestic species and breeds that were until now largely excluded from the dominant
productive systems. In conclusion, a more holistic approach of research targets is required in which physiological functions and
farmers’ practices must converge and respond to each particular situation in an integral, dynamic and flexible conceptual
perspective. From a scientific point of view, both for ICs and DCs, a broader range of experimental scenarios should be explored
in order to arrive at innovative practices and solutions that respect environmental, ethical and economical issues. The clear
challenge is to in evaluate the sustainability of RPSs. This includes, in our opinion, a strong interaction with other disciplines
(multi- and trans-disciplinary conception), thus structuring new relevant indicators for the evaluation sustainability.
Keywords: ruminant, sustainability, feeding, adaptive capacity, environment
Implications
Without providing a ‘recipe’, this review discusses the tradi-
tional and more updated aspects related to the basis of
feed resources, feeding strategies for shifting current feeding
and nutrition of ruminants to more lignocellulosic-based diets
and issues of biological animal adaptability mechanisms that
should be considered for achieving adequate system plasticity
with the ‘ideal animal’ for each particular situation.
Introduction
Recent and relevant events have covered two current
global key themes: hunger and climate change. The World
Summit on Food Security (November, 2009) and 15th
United Nations Climate Change Conference in Copenhagen
(COP15; UNCCC, 2009) ratified and updated the world lea-
ders’ positions around what they denominated as ‘our tragic
achievements in these modern days’. A declaration pledging
renewed commitment to eradicate hunger from the face
of the earth sustainably and at the earliest date, and the
-
E-mail: bocquier@supagro.inra.fr
1258

‘Copenhagen Accord’ signed by 115 heads of state or gov-
ernments taking on responsibility for limiting growth of
greenhouse gases (GHG), were their respective and more
tangible outputs. Livestock production and, specifically,
ruminants, are actively involved in both global goals.
The Food and Agricultural Organization estimates that
1.02 billion people were undernourished worldwide in 2009.
There are more hungry people now than at any time since
1970, the earliest year for which comparable statistics are
available (FAO, 2009a).
Furthermore, while commodity prices have always fluctuated
with changes in supply and demand, world agriculture now
appears to be undergoing a structural shift towards a higher
demand–growth path. Many countries, especially those in Asia,
have entered a period of faster economic growth, generating
demand for more meat and dairy products (FAO, 2007). In
addition, projected growth in agrofuel demand over the next
decade is likely to push commodity prices 12% to 15% above
the levels that would have prevailed in 2017, if demand for
agrofuels were held at 2007 levels (OECD-FAO, 2008). Looking
ahead, it is expected that agrofuels will remain a significant
source of increased demand for agricultural commodities – and
for the associated resources used to produce them.
In such a contemporary scenario, ruminants are considered
to play an important role. However, ruminant production
sustainability constitutes a hot topic that has been the subject
of numerous publications and conflicting reports in recent
decades (Delgado
et al
., 1999; Steinfeld
et al
., 2006; The
World Bank, 2009).
In this study, we focus on key points contributing to effi-
ciency of ruminant production in developing (DC) and
industrialized countries (IC), as well as the basis for con-
tinuing in the future, and facing the challenges of the new
context. We update basic and relatively new strategies on
feeding/nutrition and discuss interesting mechanisms on
animal adaptability (see Figure 1).
Our vision is to conceive a permanent feedback in the
conceptual base development and experience exchange in a
common and global strategy for both, the DCs or ICs. Flex-
ible, dynamic, integral and holistic thinking is essential for
an adequate interpretation of our perspective about the
problem we are dealing with (Figure 1). The sustainability of
ruminant production systems (RPS) will pass by warranting
the sustainability of their feeding systems (FeSysts).
General overview of the current status of ruminant
production at the global level
In general, when we (scientists) talk of ‘ruminants’, imme-
diately it is assumed that we are talking about the most
common domestic large (cattle (dairy, beef or multipurpose),
buffalos) and small (sheep, goats (dairy, meat, wool, cash-
mere, dual or multipurpose)) traditionally used species.
However, in practice, there are other less known and studied
ruminant species that feed, and actually contribute to the life
of millions of inhabitants all over the world (e.g. camels in
arid and semi-arid regions; llamas and alpacas in the Andes;
yak in Highland Central Asia and reindeer in Circumpolar
Figure 1 Sustainability of ruminant agriculture is the overall result of the interaction among multi-dynamic functions. That is warranting a rational progress
at all levels (farm, local, regional, national and international) without compromising environmental stability (i.e. avoiding soil erosion, desertification
or greenhouse gases emissions), whereas contributing to food security and poverty alleviation programmes. Rational feeding and nutrition systems are
essential in this goal.
Sustainability of ruminant production in a changing world
1259

Eurasia). The lack of literature in such ‘forgotten’ species is
immense. In our view, for a better future, animal science
must take into account the much broader spectrum of
ruminant species more seriously.
Table 1 shows the population change during the last two
decades for the main domesticated ruminant species,
according to the regions of the world. Although the most
dramatic growth in cattle populations over the period 1984
to 2004 was posted in smaller countries such as Gabon (up
463% to 35 000 head), Djibouti (249% to 297 000), Egypt
(123% to 3.9 million) and Cambodia (108% to 3 million), the
largest absolute increase in national herds was recorded by
Brazil (up 64.3 million), China (47.5 million) and Sudan (17.3
million). In contrast, led by the United States (down 18.5
million) and the European Union (EU) – following reform of
the Common Agricultural Policy – herd numbers in many ICs
fell. Thus, by 2004, over three-quarters of the global herd
were to be found in DCs (.66%; Table 1; FAOSTAT, 2009).
Water buffaloes are found primarily in southern Asia,
where they are used as both draft and dairy animals. Over
half of the global buffalo population of 172.7 million resides
in Asia, with three countries (India, Pakistan and China)
accounting for 85%, and 10 countries contributing 97% of
the global total. India harbours the highest number of cattle
(around 210 million) and buffaloes (around 84 million).
Sheep are distributed more widely, with 131 countries
reporting flocks in 2004. Nine countries, headed by China
(157.3 million head), have national flocks of over 25 million,
accounting for 52% of the global population. Sheep numbers
in ICs have fallen by 35% over the last 20 years (Table 1), in
large part due to the decline in sheep flocks in countries that
were formerly part of the USSR (down 90.7 million head
262%) or under Soviet influence in Eastern Europe, in Australia
(32%) and New Zealand (43%). Sheep numbers in the DCs
have grown by 106 million head to 691.8 million (up 18%) –
with the biggest increase in China, Sudan, Iran and India.
Goat herds are largely concentrated in DCs (96%; Table 1)
where they provide hides, milk, meat and mohair. The sharp
increase in the global goat herd (1297 million – up 62%) is,
once again, attributable largely to a substantive increase in
Chinese (169%), Bangladeshi (154%), Pakistani (91%) and
Indian (21%) stocks. Many African countries have seen a
doubling in their goat herds, aided, in part, by the promotion
of the acquisition of goats as a means of consolidating food
security and livelihoods in the region.
Such a majority of ruminant populations in DCs, and the
most recent tendencies, support the idea of the importance
of paying more attention to what is happening in these
regions. In addition, responding to the challenges posed by
global warming, oil market and the emergence of agrofuels
sector, will require a paradigm shift in the practice of agri-
culture and in the role of livestock within the farming
system. It should aim to maximize plant biomass production
from locally available diversified resources, processing of the
biomass on farms to provide food, feed and energy and
recycling of all waste materials (Preston, 2009).
Feeding and nutrition of ruminants in the new context
The feed resources: redesigning strategies
If we assume that competition for feed/food use (e.g.
between ruminants and non-ruminants or non-ruminants
Table 1
Population of the main domesticated ruminant species by world region and its changes during the last two decades
Specie Population (millions of head)
World region 1984 2004 Percentage of change Percentage of Global population
Cattle
Developing 827.7 1018.4 23.0 76.3
Developed 426.1 316.1 225.8 23.7
Total 1253.8 1334.5 6.4 –
Buffaloes
Developing 132.7 172.0 29.6 99.6
Developed 0.5 0.7 40.0 0.4
Total 133.2 172.7 29.7 –
Sheep
Developing 585.1 691.8 18.2 66.6
Developed 534.0 347.0 235.0 33.4
Total 1119.1 1038.8 27.2 –
Goats
Developing 455.4 748.0 64.3 95.9
Developed 27.2 32.0 18.5 4.1
Total 482.6 780.0 61.6 –
Camels
Developing 17.7 18.6 5.1 98.4
Developed 0.3 0.3 – 1.6
Total 18.0 18.9 5.0 –
Source: FAOSTAT, 2009.
Bocquier and Gonza
´lez-Garcı
´a
1260

and humans) is still a crucial criterion, future ruminant
FeSysts should focus preferably on maximizing the use of
lignocellulosic feedstuffs (i.e. agro-industrial by-products),
which, in most cases, represent an environmental threat.
However, eventual competition for lignocelluloses in the
second generation of agrofuel systems must be considered.
In times of rising energy claims, it seems opportune to
remember that plants are by far the most important, and the
only renewable, energy-producing source, the only basic
food-manufacturing process in the world (Ensminger
et al
.,
1990). Transformation of this primary resource is done by
herbivores and is highly optimized by ruminants with their
morphological and physiological adaptations for converting
roughage and low-quality fibrous sources efficiently and
directly into useful goods for humans. This statement is
basic, but it is relevant to keep it in mind for the future and
success of ruminant agriculture. The need to optimize the
capture of solar energy will become increasingly important
as the world enters the oil decline phase.
In integrated crop-livestock production systems, using
fibrous resources as a direct raw material for energy pro-
duction at the farm level gives another dimension to
enhancing farm sustainability. Net plant productivity has to
be addressed, especially in tropical countries with their
access to abundant energy from the sun. For example, after
the extraction of sugarcane juice (which is used for animal
feeding), bagasse is used for gasification (Preston, 2009).
Pasture and range forages
. Although the trend during the
recent decades has been to feed more concentrated feeds
widely, more than 50% of the feed consumed in the RPS
nowadays consists of forage (harvested roughage and pas-
ture) and their conserved forms (hay, silage). Thus, despite
human pressure, ruminants ‘insist’ on their preference (and
physiological need) for herbage. Approximately 60% of the
world’s pasture land (almost half the world’s usable surface)
is classified as grazing land (de Haan
et al
., 1997). In ICs,
for example, roughage accounts for more than 60% of
all livestock feed, even in a context in which feedlots and
high-technology industry dominate the market.
In traditional ruminant-producing regions, grass-based
systems of milk production predominate. For example, in
New Zealand, virtually all dairy production is based on the
grassland, with over 90% of the total nutrient requirements
coming from grazing (Hodgson, 1990). In the EU, over 95%
of milk production is based on the grassland, which is often
managed intensively.
In DCs (e.g. tropics and subtropics), finding the ideal
conditions for grain/cereal production is often thought to be
difficult. Farming systems rely strongly on the use of local
pastures and forages, going from small stakeholders with
few animals, few land and cut-and-carry-based systems (e.g.
rustic confinement for goat production in Central and Latin
America; agriculture of subsistence) to large extensive grazing
systems with large amounts of land dedicated to natural
and/or genetically improved grasslands (e.g. beef production
with the local
Brahman
herd in natural grasslands in Brazil).
The great natural biodiversity of the tropics and subtropics
positively supports a great spectrum of alternatives.
Extensive grasslands cover about 25% of the world sur-
face and contribute to the livelihoods of more than 800
million people, including many poor smallholders. However,
about 20% of the world’s pastures and rangelands, with
more than 70% in dry areas, have been degraded to some
extent, mostly through overgrazing, compaction and erosion
created by livestock keeping. Dry lands are particularly
affected by these trends, as livestock are often the only
source of livelihoods for the people living in these areas.
Clearing of land for feed crop production and expansion of
pastures for livestock production have been the driving for-
ces behind deforestation, which causes significant environ-
mental damage, releasing enormous amounts of CO
2
into
the atmosphere and causing the extinction of many animal
and plant species each year (FAO, 2005 and 2008). Solutions
in that direction are imminent. Mixing grazing systems (i.e.
agrosilvopastoral, with grasses, legumes, shrubs and trees),
for example, would avoid this tendency while enhancing
livestock production in the context of biodiversity protection
and harmony with nature.
Exploiting traditional techniques of forage conservation
(hays, silages) will continue to be strategic to alleviating
seasonal effects (e.g. drought and winters) and optimizing
forage use at the farm level (Nussio and Ribeiro, 2008; Orosz
et al
., 2008).
Grains and high-energy feeds
. Classically, intensive live-
stock production ‘laws’ dictate that, ‘to maximize produc-
tion’, the livestock producer must use a high-energy ration –
that is, a high caloric density and digestibility (e.g. low fibre
content). In grain-producing countries (e.g. ICs), a great part
of the livestock energy requirement has been traditionally
warranted by local cereal production (e.g. maize, wheat,
barley, rice, oat and sorghum).
Nevertheless, grain production is becoming highly attractive
for the agrofuel industry, shifting the priorities of grain produ-
cers in ICs and raising commodity prices, which encourages
expansion in the global production of cereals. However, the
supply response has been concentrated mostly in ICs and
among DCs, in Brazil, China and India (FAO, 2009b).
Rising maize and soyabean prices due to agrofuel produc-
tion makes it more difficult to use them in animal production
from a stable and sustainable perspective. The immediate
solution for the livestock sector is to centre attention on the
possibilities of becoming less dependent on cereals and oil-
seeds in their FeSyst strategies. Livestock keepers are aware,
and therefore, strategies such as using energetic by-products,
arebecomingmoreimportant.
In contrast, in the majority of non-cereal-producing
countries (e.g. humid tropics, DCs), expensive cereals have
to be imported unless they are replaced by the vast amount
of energy feed resources that are available locally (e.g. cas-
sava, sweet potato, yam, taro, breadfruit and sugarcane).
Therefore, the use of cereals is concentrated in non-ruminant
production (e.g. broilers, laying hens and swine). The efficient
Sustainability of ruminant production in a changing world
1261

utilization of such local resources in the tropics and sub-
tropics is a key aspect in which sound and sustainable
technologies, which are also feasible from the practical point
of view, are imperative (Gonza
´lez-Garcı
´a
et al
., 2009a).
Ruminants (and herbivorous non-ruminants) can also
obtain a large proportion of their energy needs through the
consumption of forage. The challenge is how to meet pro-
duction demands (e.g. finishing rations for beef cattle)
without replacing dietary forage at such high levels (e.g.
>85% of the concentrate in the feedlot).
The by-products of grain milling, fats, oils, fruits, nuts,
roots and specialized feeds such as molasses, often provide
excellent alternatives. In the tropics, among the best-known
examples are the use of sugarcane molasses and fresh or
dehydrated citrus pulp (Preston, 1986).
In the case of roots and tubers (e.g. potatoes, sweet
potatoes, chufas, cassava, beets, mangels, carrots and
turnips), despite their high-yield nutrient per hectare, the
cost of labour needed to harvest these crops has been, in
some way, the main disadvantage in using them in a more
extensive way. In addition, their high moisture content has
contributed to their low use in ‘standard technologies’ for
animal production. Some advances have been made in
avoiding these limitations by processing the raw material
into flour or dry meal; however, basically, mostly in DCs,
there are many technological limitations that do not encou-
rage the use of these important resources.
Fats also enable animals to meet their high-energy
requirement with less feed. A small amount of fat is desir-
able, as fats are carriers of the fat-soluble vitamins in the
ration and control dust in feed processing, facilitate pelleting
and increase palatability. With the rumen-protected fat sys-
tem, utilization of fat by the ruminant can also be improved
by altering the ratio of the saturated-to-unsaturated fatty
acid profile in carcass depot fat. However, factors that limit
the utilization of large amounts of fat by ruminants include
the inhibitory effects on rumen fermentation, lower intest-
inal absorption at high intake, low contribution to total oxi-
dation of nutrients and sensitivity to nutrient imbalance,
causing reduced energy intake (Kucuk
et al
., 2004). Recently,
there has been some interest in the use of unsaturated
sources with positive results (i.e. olive oil; Molina-Alcaide
and Ya
´n˜ ez-Ruiz, 2008).
Protein supplements
. Among the most recognized protein
supplements protein sources coming from plant processing,
the corn gluten feed or meal, the pulse grains and other forage
legumes can be cited. From processing rich oil-bearing seeds,
protein-rich products of great value, such as livestock feeds,
are obtained. Among such high-protein feeds are meals from
soyabean, coconut, cottonseed, linseed (flax), peanut, canola
(rapeseed), safflower, sesame and sunflower seed. Oil is
extracted from the seeds by one of the basic processes or
modifications, such as solvent extraction, hydraulic extraction
or expelled extraction, the feeding value being determined by
the method of extraction. The availability and digestibility of
amino acids (AA), the concentration of minerals and vitamins
and the level of moisture, fibre and urease can all affect the
efficiency of oilseed meal in a livestock ration. These sources of
protein feeds are used very often in ICs, where the ideal natural
conditions and infrastructure for such processing are available.
Pulses, the seeds of leguminous plants, are used primarily for
human consumption, but they can be fed effectively to live-
stock. Although there are more than 13 000 species within the
Leguminosae
family, only about 20 species are used for food
and/or feed. Soyabeans and peanuts are pulses, but they are
used almost entirely as oilseed meals in livestock rations. Pulses
contain components that possess anti-nutritional properties,
like proteases inhibitors, goitrogens, cyanogens, anti-vitamins,
metal-binding factors, lathyrogens and phytohemagglutins.
Processing procedures, such as cooking, germination and
fermentation can reduce their potentials risks.
In recent years, there has been increased interest in for-
mulating diets to provide a specific array of AA to the small
intestine. One of the theoretical advantages is that the
amount of crude protein (CP) included in the rations can,
potentially, be reduced, resulting in a positive economic and
environmental impact (Bach
et al
., 2000).
Agro-industrial by-products (AIBP) and crop residues
. Tra-
ditionally, producing and processing animals and plants
for food for people and feed for animals result in many
by-products and crop residues, which can be utilized as
livestock feed (Molina-Alcaide and Ya
´n˜ ez-Ruiz, 2008; Vasta
et al
., 2008). With the emergence of agrofuel production,
another important source of by-products has appeared.
Generally, crop residues are invariably fibrous, of low
digestibility and are low in nitrogen. They are often produced
on the farm and, therefore, are spread widely geographically.
Very often, on small farms in DCs, they form the main feed
for the ruminant livestock (Preston, 1986; Ben Salem and
Smith, 2008).
AIBPs result from the processing of crops, such as oilseeds,
sugarcane, citrus, pineapple and bananas, and in those regions
in which animal wastes are not prohibited, from the slaughter
andprocessingoflivestockand fish. They are restricted geo-
graphically to the factory or processing sites. Generally, they
are rich in protein (oilseeds and meals of animal origin) or
sugar (molasses, citrus and pineapple pulps) and occasionally
in starch (reject bananas, cassava peels) and usually are low in
fibre. Notable exceptions are sugarcane bagasse, palm-press
fibre, coffee pulp and cocoa pods.
These days, there is a large amount of accumulated
knowledge on the use of crop residues and AIBPs as part of
the diet of growing, gestating or lactating animals. This
approach is seen very often in mixed farming due to the
benefits of integration between agricultural and livestock
systems. Feed cost may be lowered by including such alter-
native feeds in the ration. However, when determining the
economy of AIBPs and crop residues, consideration should
be given to the costs of the nutrients supplied, transporta-
tion, storage and losses as well as possible variations in
nutrient content caused by changing milling and processing
procedures, palatability, possible toxicity or contamination
Bocquier and Gonza
´lez-Garcı
´a
1262

with pesticides or heavy metals, effect on the digestibility
and utilization of the total ration, and labour cost in feeding.
Hence, reduced animal performance and lesser profit can
result from improper feed substitution.
Ruminant nutritionists must be aware that these feed sour-
ces will play a very important role in the options of raw mate-
rials for livestock feeding in the future and, in that direction, a
great job for adapting FeSysts and routines is waiting.
Feed supplements: additives
. Along with the production of
new feeds, new chemicals, pre- and pro-biotics and growth-
promoting factors have been developed and tested exten-
sively for safety and efficacy. The list of feed additives has
been growing, with each new product offering ways of
improving the rate and/or efficiency of production.
In intensive systems, the successful livestock producer uses
supplements, additives and sometimes implants to maximize
performance, to improve animal health, to increase feed intake
and, hopefully, feed efficiency, and/or to alter some physiolo-
gical process in the animal that will stimulate production and/or
improve the quality of the product. This is very often the case in
highly intensive productions in IC settings. However, in DCs, in
most of the cases, the use of some of these products normally
arrives once they have been evaluated in some research station.
There is almost a unanimous ignorance about using additives
by farmers from the poorest DCs.
As the symbiosis occurring in the rumen has energy
(losses of methane) and protein (losses of ammonia N)
inefficiencies, modification of rumen microbial fermentation
directed at decreasing losses has become a research priority.
One of the main objectives is to evaluate alternative pro-
ducts (e.g. saponins, tannins, essential oils and other plant
extracts) as alternatives to the use of antibiotic ionophores
as additives in ruminant diets.
Calsamiglia
et al
. (2007) reviewed the research advances in
evaluating plant extracts and essential oils as modifiers of
ruminal fermentation. Using several plant extracts (whose
antimicrobial activity is attributed to a number of secondary
plant metabolites) in
in vitro
or
in vivo
conditions has resulted
in the inhibition of some ruminal bacteria, which depresses
the deamination and methanogenesis processes. This results in
lower ammonia N, methane and acetate, and in higher con-
centrations of propionate and butyrate. However, the effects of
such products have been shown to be pH and diet-dependent,
thus arriving at the conclusion that their benefits may be
obtained only under specific well-controlled conditions and RPS.
This fact complicates their acceptance at a commercial level,
together with other issues of management feasibility, actual
commercial prices or mixing filiations with other ingredients.
As this is a promising line of research with both produc-
tive and environmental possible impacts, future advances
in knowledge, and also in the application of this group
of potential products under commercial conditions, are
expected. In this regard, Calsamiglia
et al
. (2007) discuss
important aspects that need to be taken into account in the
future for effective utilization. They include the necessity of
continuing to study the optimal
in vivo
dose in units of the
active component, considering the potential adaptation of
microbial populations to their activities, examining the pre-
sence of residues in milk or meat and demonstrating
improvements in animal performance.
Priorities for future ruminant feeding and nutrition
researches
First, as mentioned above, from our view, future research in
ruminant feeding and nutrition must focus on a broader
spectrum of scenarios, thus working with normally ‘for-
gotten’ or sub-estimated ruminant species and breeds and
enhancing basic research in the tropics and subtropics (i.e. to
elucidate complex interactions in grasses and legume asso-
ciations). In addition, following the integrated, holistic
approach of mixed farming systems, future RPS should
consider its possible integration with non-ruminants pro-
duction at farm or regional levels (Figure 1).
Complementarities of multiple crop associations are a
priority for the development of new, relevant methodologies
for a better understanding of, for example, diet selection in
grazing by several types of animals (Niderkorn and Baumont,
2009). The advances in this field, similar to others, have been
developed mostly under controlled conditions, both in DCs
and ICs and in monoculture grasslands.
In the particular case of understanding rumen functioning,
the view of ruminal fermentation as the sum of activities
of the dominant rumen microbiota is no longer adequate.
A more holistic approach is required in which physiological
functions and management must respond to each particular
situation in an integral, dynamic and flexible conceptual
approach. Thus, farms in the ‘North’ must differ from the
‘South’ in their solutions, as their current problems also differ
even with similar final production purposes. Concepts gen-
erated under highly concentrated use, confinement and
genetically ‘improved’ modified breeds (e.g. feedlot in ICs)
cannot be extrapolated anymore to, for example, a bio-
diverse forage-based multi-association system (e.g. grasses
and legumes) with indigenous ‘low potential’ genotypes
(e.g. tropical agrosilvopastoral system in DCs). In the ‘North’,
emerging concepts of livestock precision farming (e.g.
assisted auto-fed animals) offer opportunities to reduce such
a gap in a useful iterative manner and could provide novel
targets for future strategies and relevant renewed research
questions. In the ‘South’, the scenario is different and
probably more complex and diverse in origins. Basic tools
(e.g. biotechnology, metagenomics for culturability and body
reserve management) actually constitute the connection
point of our scientific community at the global level.
Mathematical modelling techniques are important tools
that have been applied to the study of various aspects of the
ruminant, such as rumen functioning, post-absorptive meta-
bolism and product composition, rumen fermentation and its
associated rumen disorders and energy and nutrient utilization
and excretion with respect to environmental issues. Models
that relate rumen temperature to rumen pH have also been
developed and have the potential to aid in the diagnosis of
subacute rumen acidosis (Kebreab
et al
., 2009).
Sustainability of ruminant production in a changing world
1263

From a nutritional perspective, in our view future research
must explore the following major fields:
1. Optimization of ruminal fibre degradation from diversi-
fied sources.
2. Adequacy of protein supplementation. Warranting protein
by-pass, quality of AA profile. Anti-nutritional factors or
secondary compounds in legume-based diets and AIBP use.
3. Methane production mitigation and nutrient excretion
reduction and recycling.
Optimizing ruminal fibre degradation
. If we propose to focus
future ruminant FeSysts research on the more intensive use of
fibrous resources, then it seems logical that it will be a priority to
continue exploring new ways for optimizing fibre digestion.
While much is known about the ways in which ruminants utilize
nutrients to convert them into meat and milk, there are, based on
several decades of research (e.g. Agricultural Research Council
(ARC), 1980; Institut National de Recherche Agronomique
(INRA), 1988; National Research Council (NRC), 2001), large
gaps in our knowledge of the nutritional value of much of
the world’s grazing resources, especially from the tropics.
Although conceptual models of diet selection have been
developed, in practical terms, it is still difficult to predict the
quantity and composition of the grazing animals’ diet that
will be selected when faced with a complex array of plants.
This lack of understanding and predictive ability represents a
major limitation to the development of more efficient graz-
ing or forage-based FeSysts. For temperate systems, based
on relatively simple monocultures of ryegrass or simple
mixtures of a few plant species, some progress has been
made, but for much of the rest of the world’s grasslands,
such predictive models do not exist.
Despite the advances achieved, the actual conversion of
feeds by ruminants to animal products is still known to be
somewhat inefficient (Figure 2). Only 10% to 35% of gross
energy intake is converted into net energy because 20% to
70% of lignocelluloses may not be digested.
Varga and Kolver (1997) described the four major factors
regulating fibre ruminal digestion:
1. Plant structure and composition, determining microbial
access to nutrients.
2. Nature of the population densities of the predominant
fibre-digesting microorganisms.
3. Microbial factors that control adhesion and hydrolysis
by complexes of hydrolytic enzymes of the adherent
microbial populations.
4. Animal factors that increase the availability of nutrients
through mastication, salivation and digesta kinetics.
Increasing the efficiency with which the rumen microbiota
degrades fibre has been the subject of extensive research for
at least 100 years. It is known that the optimization of plant
cell wall (fibre) digestion may be achieved by two well-
defined strategies:
1. Using methods to ‘pre-digest’ the fibre before being
consumed by the animal.
2. ‘Helping’ the rumen achieve better fibre degradation
through manipulation of its environment and fermentation.
The first strategy made significant and recognized
advances during the last century (Berger
et al
., 1994). Several
Figure 2 Energy utilization by a lactating cow showing average partition of feed energy by the animal (adapted from Ensminger
et al
., 1990).
Bocquier and Gonza
´lez-Garcı
´a
1264

mechanical (e.g. chopping to reduce particle size), physical (e.g.
heating, toasting), chemical (e.g. ammonia, dilute acid hydro-
lysis) or biological (e.g. application of free-living lignolytic fungi)
treatments of forages have been developed more or less suc-
cessfully from the laboratory to the farms. The challenge still is
including these technologies in the normal routine of the farms.
In our view, the main disadvantage for these technologies at
the farm level is related to the serious failure in the develop-
ment of efficient extension services. Unfortunately, such kinds
of solutions are more due to a lack of efficient politics at any
level than to applying technical know-how. However, research
institutions are also responsible for a better diffusion.
Furthermore, the notion that the rumen microbiota lacks
appropriate fibrolytic activities has persisted. Recently, an
excellent review by Krause
et al
. (2003) covered the various
attempts and strategies employed for improving fibre degra-
dation in the rumen. These authors emphasize that our under-
standing of the rumen microbial ecosystem is still superficial in
comparison with the complexity it encompasses.
Varga and Kolver (1997) also stated some priorities for
research to enhance fibre digestion in ruminants. In some of
them, advances have been made. However, others will need
further effort. For example, even when fungi exert a significant
role in fibre digestion, there is still a lack of information about
the interaction and synergisms between the bacteria and fungi
populations during the attachment, adhesion, penetration and
consortia formation in the digestion process. More information
is also needed on the microbial fermentation rate
v.
growth
rate as affected by the nutrient requirements of ruminal
microorganisms. Genetic management of ruminal flora will
need further advances and greater detail in the understanding
of the processes, as well as the enzymatic and adhering cap-
abilities of microorganisms that attack the most refractory
sources involving the lignin–carbohydrate bonds.
The reader should refer to Krause
et al
. (2003) and other
extensive lists of studies for further information on chemical
and mechanical treatments, plants genetically modified for
plant cell wall composition (e.g. lignin synthesis – changes to
the components of lignin result in improvements in digest-
ibility – or cellulose synthesis; e.g. Cherney
et al
., 1991;
Sewalt
et al
., 1997; Turner
et al
., 2001), lignolytic fungi (e.g.
Akin
et al
., 1995; Mayer and Staples, 2002; Sun and Cheng,
2002) and exogenous enzymes (McAllister
et al
., 2001;
Beauchemin
et al
., 2004; Gonza
´lez-Garcı
´a
et al
., 2009b).
Yeasts (Chaucheyras-Durand
et al
., 2008), fibrolytic
enzymes and other feed additives (Horton, 1980) have been
widely evaluated in recent years with a lack of consistency in
the results that have been obtained. The complexity of the
rumen and the great diversity of situations at the farm level
contribute to such inconsistency. However, these are also
valuable resources on which nutritionists must continue to
work with standard methodologies of evaluation.
Adequacy of protein supplementation
. For more than a
century, protein supplements and AA have been studied and
recognized as essential dietary constituents. However,
before 1890, no one was concerned about adding protein
supplements to livestock rations. As an anecdote, in the
United States, the flour mills in Minneapolis dumped wheat
bran into the Mississippi River because nobody wanted to
buy it, cottonseed meal was used as fertilizer, if used at all,
while soyabeans were little known outside the Orient
(Ensminger
et al
., 1990). Many of the by-products that once
were pollutants are now in unprecedented demand.
In the current scenario and the imminent competition for
cereals with the agrofuel sector, future sustainable RPS will
have to consider more seriously the use of forage legumes
and safe protein AIBPs. We have to harvest or graze our
forage till the optimum maturity stage point (Archime
`de
et al
., 2000; Boval
et al
., 2007), and we have to profit more
from those high-protein forages by establishing and mana-
ging them at the farm level. We have to plant and manage
legumes others than soyabean (for grain production). We
have to exploit the vast forage germplasm existing world-
wide in several latitudes (see the CIAT-CGIAR website avail-
able at http://isa.ciat.cgiar.org/urg/language.do;jsessionid5
96938AECC788127301C75D4179F0ECE4). This approach is
particularly important in DCs.
Legumes have good levels of CP and are used in grazing
(e.g. association of grasses and legumes) or cut-and-carry
systems generally for use as protein supplements. Because
of their content in secondary compounds, they are able to
‘protect’ CP from rumen degradation. The development of
agrosilvopastoral and agroforestry systems for animal pro-
duction (see Maurı
´cio
et al
., 2008) relies on the essential role
of such plants as a cheap and valuable source of protein
at the farm level in a biodiverse, iterative and dynamic
context. These systems have caught the attention of farmers,
specialists, researchers and extensionists in recent decades,
mostly in the tropics and the subtropics. Without doubt,
advances in such fields have contributed during the
last times to the poverty alleviation in the poorest regions
of DCs through an improvement of animal production
indicators.
There is also a group of plants that are not legumes and
have been included successfully in such strategies (e.g.
mulberry
Morus
spp.,
Trichantera gigantea
). A good collec-
tion of applied and basic research results is available in
the
Agroforestry Systems
and
Livestock Research for Rural
Development
(LRRD) journals or on the websites of impor-
tant institutions such as CATIE, CIPAV and ILRI.
However, the presence of secondary compounds in
legumes may affect voluntary intake, digestibility, animal
health and final product quality. A lot of research has been
devoted to this subject in recent years. As an example, the
lower intake of tannin-rich feeds is attributed generally to
their astringent taste. In addition to this unpleasant taste,
the lower rate of digestion (higher rumen fill) in the presence
of tannins could also be responsible for the lower feed
intake. The effect of bound tannins on digestion is not
necessarily related in any way to that of free tannins.
It will be important to conduct studies on the relationship
between tannin structure and activity. Although research on
tannins has a long history, considerable additional research
Sustainability of ruminant production in a changing world
1265

is required to exploit the benefits of fully incorporating
legumes and AIBPs in livestock feed (Reed, 1995; Makkar,
2003).
In addition, very little is known in the area of ‘anti-
nutrient–antinutrient’ interactions (e.g. tannins–saponins)
from the perspective of different feed sources, which should
be explored further. They as are likely to have immense
nutritional and ecological significance. This area of research
will need continuous effort in the near future.
Moreover, extensive research has shown that global
protein efficiency can be increased by protecting some pro-
teins (or AA) from ruminal degradation.
Methane production mitigation, nutrient excretion reduction
and recycling of farm waste
. The root cause of the past and
projected climate change is now recognized to be the warming
potential of a number of GHG. Like all other human activities,
development and use of intensive animal production systems,
including those with ruminants, contribute to environmental
pollution due to the waste output (Tamminga, 1996).
Anthropogenic processes are responsible for between
55% and 70% of the estimated 600 T
g
of methane that is
released annually into the atmosphere (Intergovernmental
Panel on Climate Change (IPCC), 2001), with studies sug-
gesting that ruminant eructation is one, if not the main,
anthropogenic source (Table 2). Enteric fermentation is a
major contributor to emissions in a number of countries
(Thorpe, 2009).
Around 90% of methane is produced in the rumen and
98% of the enterically produced methane is released
through the nose and mouth (Johnson
et al
., 2000). Johnson
and Johnson (1995) and Johnson
et al
. (2000) have sug-
gested that methane yields in cattle may vary from 2% to 3%
(if fed a high-concentrate diet) to 10% (when fed a very poor
quality diet), with most diets at most feeding levels produ-
cing methane yields in the range 6% to 7% of the gross
energy intake.
Research findings recognize that both management prac-
tices and feeding schemes could have substantive impacts on
mitigating methane emissions.Reducingherdsizesand
adjusting livestock FeSysts have been among the main stra-
tegies that have been proposed. The propensity of certain
additives to reduce ruminal methane production (Calsamiglia
et al
., 2007) and emissions effectively is also a possible tool in
which research has to make further advances.
As using more fibrous diets is a target in the current
situation, this will drive the shift towards lower energy
density and, therefore, increasing the risks for more methane
production and emissions, which means a challenge for
ruminant physiologists.
A large number of compounds can reduce methane pro-
duction (i.e. halogenated methane analogues, oils, essential
oils, organic acids, fructan and even antibiotics such as
monensin). However, halogenated compounds are unlikely
to be approved for administration to animals, and responses
to oils can be variable, especially in the long term, while
organic acids and fructans are prohibitively expensive
(Waghorn and Clark, 2006) and the use of antibiotics is
banned in some regions, like the EU.
In the short term, in extensive grazing systems, there are
no cost-effective methods able to achieve substantial
reductions in GHG emissions from grazing systems. More
opportunities for intensive grasslands exist because high-
input systems are more amenable to improvements in pas-
ture, fertilizer and animal management.
A combination of pasture improvement, management
and animal selection will, for sure, reduce GHG/unit pro-
duction but not necessarily absolute GHG emissions. A multi-
faceted approach towards mitigation, with lower forage
nitrogen concentrations and use of lifecycle analysis to
integrate all inputs, will identify the best opportunities for
immediate application (Waghorn and Clark, 2006).
On the other hand, much of the effort expended on
nutrient management has focused on the post-excretion
product. It is important to keep in mind that the manage-
ment of the diet can have an important impact on the
quantitative and qualitative aspects of the excreted nutrient
(critically N and P). This is another environmental challenge
for future ruminant sustainability. It is easier to control
potential pollutants by managing their release into the
environment than to recover or confine them once they have
been released.
High-forage diets also contribute to the absorption of
NH
3
N from the rumen because of the higher ruminal pH
associated with these diets. Nitrogen losses may also impair
animal performance. Energy supplementation of diets based
on fresh forage has been shown to increase non-ammonia
Table 2
Enteric emissions of CH
4
from the main domesticated ruminant
species by world region and its changes during the last two decades
Specie Annual CH
4
emissions (T
g
)
World region 1984 2004
Cattle
Developing 32.43 39.82
Developed 23.77 17.67
Total 56.2 57.49
Buffaloes
Developing 6.64 8.60
Developed 0.03 0.04
Total 6.67 8.64
Sheep
Developing 2.93 3.46
Developed 3.85 2.49
Total 6.78 5.95
Goats
Developing 2.28 3.74
Developed 0.14 0.16
Total 2.42 3.90
Camels
Developing 1.03 1.08
Developed 0.02 0.02
Total 1.05 1.10
Source: FAOSTAT, 2009.
Bocquier and Gonza
´lez-Garcı
´a
1266

nitrogen flow to the duodenum, reduce ruminal NH
3
N
concentrations and improve animal performance.
Balancing rumen undegradable and degradable proteins,
and use of protected methionine along with the strategic
selection of protein supplements that are relatively rich
in lysine, may permit a 10% to 15% reduction in total N
excretion, with most of the reduction occurring in urinary N.
Urinary urea, following conversion to NH
3
, is the N excretion
product most vulnerable to loss to the environment. More
accurate formulation of diets for protein provides an oppor-
tunity for reducing N excretion. This would translate into
a reduction in N excretion and NH
3
volatilization in open-
dirt pens.
Importantly, manure recycling at the farm (and regional)
level is an ideal solution to ‘close the cycle’ in a more
holistic manner (Figure 1). Returning limiting nutrients to
the soil (i.e. organic fertilization) and producing energy
(i.e. through biogas) are among the best-known benefits
(Preston, 2009). This solution of integration between agri-
culture and livestock systems would be ideal for applying
to all scales.
Biological adaptive capacities of ruminants
in situations of feed supply variation
Classically it has been considered that nutrient requirements
include maintenance and the costs of productive functions
(ARC, 1980; INRA, 1988; NRC, 2001). Although not fully
exact, the immediate consequence of such an assumption is
that the aim of breeders is to limit the length of unproductive
periods (e.g. ensuring the success of reproduction).
Feeding practices of ruminants at maintenance
Even at maintenance, there are possibilities of saving diet-
ary energy and nutrients thanks to the capability of the
animal to reduce its whole metabolism under conditions of
limited feed supply. This adaptive capacity involves several
phases of sparing mechanisms avoiding the use of classical
limiting substrates in the ruminant (glucose, essential AA)
and mobilizing endogenous tissue substrates to fulfil the
energy expenditure (Chilliard
et al
., 1998). In this case,
homeostatic regulations operate to warrant the longest
individual survival (Atti and Bocquier, 1999; Bonnet
et al
.,
2000). Inversely, for a given animal, it has been shown that
maintenance requirements are increased in fat animals
(cows: Agabriel and Petit, 1987; ewes: Bonnet
et al
., 2000).
As another regulatory process linked with leptin secretion
from adipose tissue, voluntary feed intake is reduced in fat
animals (sheep: Tolkamp
et al
., 2006; dairy cows: Faverdin
and Bareille, 1999) and stimulated in lean animals (Dela-
vaud
et al
., 2002; Gonza
´lez-Garcı
´a
et al
., 2009c). This latter
situation allows the achievement of a high level of intake
when they are refed. After a long period of energy restric-
tion, when dry mature females of ruminants are refed, a
rebound in the evolution of body weight (BW) change, lipid
re-deposition and a protein recovery is observed (Atti and
Bocquier, 1999).
Effects of feeding practices in producing animals
Homeostatic regulations that only operate in non-productive
ruminants to maintain physiological parameters within the
range of normal values are not always successful, especially in
productive animals. This, together with other physiological
arguments, has led to the concept of teleophorhesis (Chilliard,
1986), also called homehorhesis (Bauman and Currie, 1980;
Bauman and Vernon, 1993). This phenomenon, whose biolo-
gical significance is to ensure the species’ survival (e.g. during
pregnancy – foetus survival, lactation, feeding the offspring or
growth reaching mature size for reproduction), is an upper
regulatory level. It allows explaining how the integrity of the
organism is maintained while supporting the metabolic orien-
tations towards production and establishing saving and recy-
cling mechanisms. It could be considered as a driving force of
nutrients partitioning exerting a ranking of priority of biological
functions at a given physiological stage. For example, milk
production in early lactation and replenishment of body
reserves at the end of lactation (Chilliard, 1992; Kharrat and
Bocquier, 2010).
Such ability to cope with variations of nutrient balance
allows development of original feeding strategies as ruminants
are able to support transient periods of underfeeding while
producing. Conversely, they can store body reserves when feed
supply is above total energy requirements. This has already
been put into practice in dairy cows that can deposit body
energy with high efficiency (NE/ME 5Kl 50.60) at the end of
lactation and can further mobilize this body energy into milk
with an even higher efficiency (Krl 50.80, INRA, 1988). Even if
the whole process is less efficient (0.48) than direct milk pro-
duction (Kl 50.60), it may avoid the use of large amounts of
concentrate. Another classical feeding strategy that is used in
beef cattle production, relies on the ability of winter underfed
animals to regain BW (compensatory growth) when refed with
low-cost feeds (spring grazing). Digestive and metabolic
adaptations in this rebound period are effective within few days
(Hoch
et al
., 2003), showing the reactivity of the organism to
benefit from an improvement in its nutritional conditions. Such
a strategy can be successfully applied to dairy heifers (Ford and
Park, 2001).
Feeding costs reduction related to specific production system
The cost of energy for thermoregulation (Thatcher, 1974;
West, 2003) and for walking activities (Coulon
et al
., 1998)
has often been an argument to place animals in confinement
(Blake
et al
., 1982). This could not be avoided in more
extensive farming systems, but this cost has to be re-eval-
uated because there are conflicting results in the literature.
Coordinated biological responses of ruminants:
opportunities for achieving the system plasticity
Effects of genetic potential on response laws
An increment in the performance of ruminant specialized
breeds in ICs is well documented, with only slightly differing
objectives among countries (Miglior
et al
., 2005; Hayes
et al
., 2009). In contrast, productive results of local breeds in
Sustainability of ruminant production in a changing world
1267

DCs are considerably less documented and, consequently,
less reliable. In addition, numerous transfers of improved
dairy cattle from temperate zones to harsh environments
revealed that performance were considerably lower due
to the recognized effects of genotype–environment interac-
tions (Hammami
et al
., 2008). The approach to analysing
the exact causes of difficulties encountered with highly
selected ruminants, even in ICs, is now questioned (see
Blanc
et al
., 2006; Friggens and Newbold, 2007; Friggens
et al
., 2010).
For reducing the length of the unproductive periods, the
success of reproduction is crucial. Considering the repro-
ductive rhythm of the species in the temperate climate,
reproduction rates are often close to the theoretical biolo-
gical limits of the species: calving interval being close to
1 year in cows and three lambings in 2 years in sheep
(Robinson
et al
., 2006). In the sub-tropical climate the
N’Dama cows have a much longer average breeding interval
(e.g. 2.3 years) and age at first calving is around 5 years
(Ezanno
et al
., 2003). As the constraints in the sub-tropical
climate are higher than in temperate zones there is a natural
separation between pregnancy and lactation. Reproduction
occurs when cows have dried off for almost 1 year so that
they can slowly replenish their body reserves and then, only
when feeding conditions are improved (rainy season), they
become able to support a new productive cycle (Ezanno
et al
., 2003). Furthermore, contrary to the intensively bred
cattle of temperate climates the decision to cull a cow does
not depend on its fertility.
Another biological strategy can be observed in the dual-
purpose Lebanon Balady goats fed in rangelands (Kharrat
and Bocquier, 2010). Each time the feed supply is improved
milk yield rebounds. When reaching the end of lactation milk
rebounds cease and dietary energy surplus is clearly oriented
towards the full recovery of body fat reserves. It seems that
this breed has maintained a high trade-off capability
between lactation and reproduction.
General framework of adaptive processes under innovative
feeding practices
When considering innovative feeding practices, the individual
adaptive capacity becomes central because the biological
response must be predictable and eventually controlled,
the type of responses being dependent on the genetic
potential defined at least by breed characteristics. Several
functional responses of ruminants to underfeeding con-
straints have been described and classified according to the
shape of the response curves (Blanc
et al
., 2006; Friggens
and Newbold, 2007). In the case of domestic ruminants their
adaptive response cannot be assessed only by the individual
capacity of survival or even by the species perennity but,
importantly, by the ability to sustain a given productive
function.
It could be considered that biological adaptation is the
ability of the whole organism to cope with environmental
changes either through resistance (e.g. the production is
apparently maintained in a stable condition) or through
deformations that could be considered as flexible (high
probability of returning to the initial point without any
damage; Figure 3). This includes strong elastic marginal
responses to underfeeding (if the breaking point is not
reached) but also to overfeeding (when the mechanism
induces a rebound-like compensatory growth). The response
law is described by the integration of the marginal coeffi-
cients of elasticity. In some cases, the animal may not be able
to reach its initial status because of limited rebound; the
system is then considered to be inflexible, but as it attempts
to adapt it can be considered to be plastic (Figure 3). With
plastic responses some carry-over effects may persist. In all
inflexible situations, the breaking point is reached and a dra-
matic production turn-off occurs. Of course, at a sub-level of
organization, within the organism, several biological functions
may be successively activated in order to sustain the productive
function (Chilliard
et al
., 1998) in a non-visible manner, thus
complicating the assessment of a disruption (Tillard
et al
., 2007
Figure 3 Schematic representation of response curves of a productive function (milk production, growth or reproduction) in domestic ruminants subjected to
severe feed supply changes. Interpretations of numbered steps are inserted in the text.
Bocquier and Gonza
´lez-Garcı
´a
1268

and 2008). When a biological sub-system has reached its
breaking point some other metabolic pathways may be acti-
vated, and the global response is still elastic within a given
range of intensity of perturbation or within a range of duration
of this perturbation. With regard to reproduction, it has also
been underlined (Blanc
et al
., 2006) that the introduction of a
delay in the response is also a way of adapting to inadequate
nutrition. This is particularly the case in species such as the
bovines, whose reproduction should occur during lactation at a
stage when the females are in strong negative energy balance
(see Friggens
et al
., 2010).
As the ovulation process
per se
does not require high
fluxes of energy, there is no real competition in the energy
partition between the mammary gland and the ovary; with
only a passive subordination of reproduction to the dom-
inating process occurring. Nevertheless, we can consider
that teleophoretic regulations that operate at this stage
(lipid mobilization, mammary drain of nutrients) introduce
perturbations in the functioning of the ovary whose response
is to postpone the occurrence of ovulation. Such a situation,
recognized by the breeder as a failure, may be interpreted as
the direct result of an adaptive process that ensures the
survival of the individual (the lactating female) at the
expense of the survival of the species (giving birth to a
newborn). This could be considered as an anticipative
adaptation (summarized by Friggens, 2003). Inversely, the
effect of flushing, which is a short-term positive effect of
nutrition on ovulation rates (Robinson
et al
., 2006), over-
comes the negative effect of poor body fatness.
From the physiological point of view, it can be considered
that the regulatory systems that should prevent multi-
ovulations in lean ewes are temporarily misled and an
unexpected positive response is obtained. More recently, this
idea to mislead the regulatory systems has been extended to
other biological functions and to other feeds or compounds
with the aim of eliciting a specific biological response
such as controlling the anoestrus duration (Somchit
et al
.,
2007; Vinolesa
et al
., 2009). Even if one of the main interest
could be to save expensive feeds, this feeding practice,
which was called ‘focus feeding’, may not be convenient for
all renewed FeSysts and may be at risk for some biological
functions. The applied objectives of ‘focus feeding’ are sound
and ambitious, but one must keep in mind that reasoning
a priori
the reaction of regulatory systems may be risky.
For instance, in early lactating dairy cows it was expected
that providing high-energy content feeds, such as dietary
fat, would help in reducing body lipid mobilization through
direct fat supply. Surprisingly, a meta-analysis of the data
revealed that under this focus feeding practice cows mobi-
lized more body lipids than unsupplemented ones (Chilliard,
1993).
Transferring innovative strategies to farming conditions
Under the farming conditions, ruminant FeSysts mostly cannot
be individualized and diets are normally formulated for large
groups of animals. Numerous studies has been conducted with
the objective of grouping animals into homogenous groups
expecting that their adaptive response (and the resulting per-
formances) would also be homogenous. Unfortunately, the
large variety of individual responses, even inside a class of
similar animals, mostly leads to unpredictable group responses.
Another important factor that alters the prediction is the social
behaviour and interactions (i.e. competition for feed). Thus, to
maintain homogeneity within the groups it would be necessary
to reallocate the animals. Thisprocedure is, however, delicate as
re-compositions of groups reinforce behavioural problems.
Nevertheless, some conclusions can be drawn with animals
often fed as a unique flock. From studies on dairy ewes
(diversity of milk production levels) a common feeding caused
disruptive situations in some sensitive individuals (Bocquier
et al
., 1995), precisely those that often have higher nutritional
requirements. The proportion of sensitive animals not only
depends on the variability of nutritional requirements (physio-
logical stage, production level) but also on diet characteristics
(bulk, nutritional value). However, appropriate feeding strate-
gies for bulk diet do exist. It has been shown that a common
diet avoids problem occurrence when it is warranted to fulfil the
requirements of at least 80% of the individuals in the flock
(Bocquier
et al
., 1995 and 2002). According to the often-
observed variability in milk yield, this leads to formulation of
diets that fulfil energy and protein requirements at 120% and
140%, respectively. In all situations, whatever the adjustment
of feeding practices, there is feed wastage due to the inade-
quacy of feed allowances to individual animal requirements.
Finally, the grouping of individuals with similar char-
acteristics is convenient for production planning, for work
simplification and to design feasible feeding strategies
leading to increased feed efficiency. But in situations of large
uncertainty about the availability of feed supply, this syn-
chronization clearly exposes some classes of animals to
common risks. Therefore, as a paradoxical effect, it seems
that for livestock systems in which reproduction periods are
not well controlled and where the physiological stages of the
animals are widespread, the adaptive capacity of the herd
considered as a whole may be greater than that of a cohort
of individuals with a narrow range of nutritional require-
ments. Such a strategy is often adopted in DCs (sheep: Atti
et al
., 2004; cattle: Ezanno
et al
., 2003).
One should not forget that farming systems that strongly
rely on adaptive responses may have consequences on ani-
mal welfare. As adaptive responses are also mediated by
behavioural troubles they may not be acceptable (see Martin
et al
., 2004). This important point related to the acceptability
of stress according to the cultural environment, is not in the
scope of this paper.
Conclusions on adaptive capacities of ruminants to renewed
feeding systems
If ruminants of ICs are performing in this manner, it is both
because of genetic selection and to an artificial change in
their direct environment. This has been an iteratively suc-
cessful process in terms of individual animal performance for
determined production (i.e. meat and milk) with an acceler-
ated co-evolution of their immediate environment. No doubt
Sustainability of ruminant production in a changing world
1269

that this general scheme gave very efficient animals from the
point of view of gross energy and protein conversion into
goods for humans. Simply considering feeds used by animals
in ICs, however, one could notice a great difference from
those consumed by ruminants in DCs, which are also far
different from their wild counterparts. Although hazardous
(e.g. ruminal disorders – acidosis – due to reduction of fibre
content of diets), these substitutions of feeds made selected
ruminants evolve from their initial trophic level of strict for-
age eaters to nearly omnivorous status, thus becoming less
dependent on primary lignocellulosic resources. However,
from the ecological point of view (Figure 4), this rising up
along the food chain imposed the use of artificial and stan-
dardized resources such as cultivated forages and grains
(selected, fertilized, harvested, treated and often transported
to very long distances). This food chain position should be
holistically revaluated through multi-criteria methods. For
instance, life-cycle analysis may allow judging their interest
not solely from the economic but also from the eco-systemic
point of view (nutrient cycles; Figure 4).
If this is not done, a clear danger is that these selected
ruminants that appear to be in direct competition with
nutritional needs of human populations, could be excluded
from the local food chain. Paradoxically, the less efficient the
ruminants are, because of their capacity of high fibre diets
consumption, the higher they are of ecological interest. The
message is that all ruminants should be kept in a proper
definite vital cycle, whatever its magnitude, which can be far
larger than a classical ecological niche. This is the central
condition for making a community of living organisms stable
and self-perpetuating. The main issue, from a technical point
of view, would be to select more robust ruminants in ICs and
to move forward more productive ruminants in DCs without
removing their natural adaptive capacity to harsh environments.
Thus, look for the ‘ideal balance’ between productive capa-
city and adaptability. Altogether it is necessary to better
control the expression of adaptive traits that are required in
each productive system.
Perspectives
This general review could not deal with several key issues
(i.e. health) that have, however, to be kept in mind (Figure 1).
Surely, ruminants will continue being essential in future food
security and poverty alleviation programmes; however, some
strategies (i.e. feeding and genetic programmes) are asking
for new ways to breed them, given the current global chal-
lenges. Whatever the country or region, the sustainability of
ruminant production will be largely determined by the
management of environmental issues, which also depend on
public institutional initiatives and decision makers’ support.
More emphasis on animal welfare will direct some rumi-
nant farming systems in regions like EU. Integration of
‘omics’ technologies (functional genomics, proteomics and
metabolomics) is a particularly exciting opportunity for the
understanding of ruminant future potentialities.
Other promissory fields on which applied research must
continue focusing from a multidisciplinary expertise include,
in our view:
1. To better know the metabolic processes and intermediary
metabolism while enhancing microbial protein synthesis
under several scenarios from dietary material to final product.
2. Helping to find alternatives for digestive limitations in
legume FeSysts related to secondary compounds content
and their bioactivity in some lesser-known plants.
Figure 4 A vision of the ecological position of ruminants from developing countries (DCs, mostly corresponding to extensive and low input systems) to
developed countries (industrialized countries (ICs), mostly highly intensified systems). Emphasis is made on nutrients cycles that may be nearly close in DCs
and widely opened in ICs.
Bocquier and Gonza
´lez-Garcı
´a
1270

3. To actively include a broader spectrum of domestic ruminant
species and breeds in future research programmes.
There is no ‘recipe,’ as so many different solutions and
diverse situations that exist at the farm level; in addition, there
are a multitude of different socio-economic and edaphocli-
matic contexts. As we have seen above, with rare exceptions
(e.g. new biotechnological findings), the feed resource base
will continue to be almost the same in the future. A great
amount of accumulated knowledge in feed processing and
utilization exists, with a large gap between such volume of
knowledge and actual farming practices. Even less is applied
from the already demonstrated biological adaptability of
animals to environmental constraints.
Furthermore, there is no ‘renewable’ alternative that can
supply energy at the same level of usage as presently occurs
with oil. Thus, economy in energy use must be a major factor
governing the choice of future farming systems. This puts
major emphasis on farm-grown inputs where external
energy costs are minimized.
The world has changed and will never be the same as when
oil was cheap and abundant. The role of livestock will almost
certainly become more important and our approach to the
development of production systems must also change. Smaller
farms with fully integrated crop-livestock systems could be
more appropriate than industrialized monocultures in a world
where exogenous energy sources are becoming increasingly
more expensive. Changes of this nature will impact strongly on
future FeSyst for all livestock, not just ruminants.
Acknowledgements
The authors thank the anonymous reviewers whose comments
helped in improving the manuscript.
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