Directory UMM :Data Elmu:jurnal:L:Livestock Production Science:Vol64.Issue1.May2000:

(1)

www.elsevier.com / locate / livprodsci

How forage characteristics influence behaviour and intake in

small ruminants: a review

a ,

_*

a b c

R. Baumont

, S. Prache , M. Meuret , P. Morand-Fehr

´ `

Unite de Recherches sur les Herbivores, INRA Centre de Clermont-Fd /Theix, 63122 Saint-Genes-Champanelle, France

´ ´

Unite d’Ecodeveloppement, INRA Domaine Saint-Paul-Site Agroparc, 84914 Avignon Cedex 9, France

Laboratoire de Nutrition et Alimentation, INA-PG, 16, Rue Claude-Bernard, 75231 Paris Cedex 05, France

Abstract

Small ruminant production systems vary widely, from high producing dairy goats to suckling ewes on rangelands. However, in all environments feed characteristics influence animals’ motivation to eat, dietary choices and ultimately nutrient intake. This review highlights the common feed factors that influence feeding behaviour and intake, although their expression and consequences depend on the environment. The main characteristics of feeding behaviour are described in terms of the satiation process and motivation to eat. The main feed factors that influence intake are then reviewed. The relationship between the nutritive value of forages and their voluntary intake is well established. The relationship between nutritive value and palatability of feeds is discussed in the light of recent work on how feed characteristics are learned. At

(2)

´ ` ´

Keywords: Intake; Feeding behaviour; Forage; Foraging; Sheep; Goat

1. Introduction depends on nutritional requirements and body

re-serves (Faverdin et al., 1995). Feed factors act

Small ruminant production systems vary widely, mainly on the short-term control.

from intensive feeding with zero grazing to the utilisation of rangelands in arid areas. In all

pro-2.1. Meal behaviour and satiation process duction systems, it is generally economically

sens-ible to maximise the proportion of forage in the diet

When fed indoors main meals are scheduled by to minimise feeding costs. Furthermore, as people

the feed distribution, usually two per day. At pasture, are becoming more and more sensitive to the image

two main grazing periods usually occur at sunrise of animal products, maximising forage utilisation is

and sunset. Post-ingestive signals coming from feed an increasingly important tool in animal production.

(rumen fill, fermentation products and nutrients) In extensive systems, grazing also contributes to

contribute to the satiation process. These feedback resource preservation. However, efficient utilisation

signals are mainly integrated in the control of intake of forage resources and control of animal impact on

to prevent excess. vegetation need thorough knowledge of what

de-Sixty to 80% of daily intake is eaten during two termines feeding behaviour and dietary choices.

main meals following distributions. Thus daily for-This paper reviews feed factors that influence

age intake is closely related to the amount eaten feeding behaviour, dietary choices and ultimately

during main meals (Jarrige et al., 1995). During a nutrient intake in sheep and goats. First, the main

main meal, the rate of intake is highest at the characteristics of feeding behaviour are described in

beginning and then decreases continuously as satia-terms of the satiation process and motivation to eat.

tion proceeds until satiety. Simple exponential Then, the ways in which vegetation characteristics

models accurately fit cumulative intake during meals influence ingestion of forage, feeding behaviour and

in both cows (Faverdin, 1985) and sheep (Baumont foraging decisions are reviewed. At pasture, two

et al., 1989). Initial rate of intake represents the different situations are considered: (i) situations

motivation to eat and the constant of deceleration of where animals are free to develop their own foraging

the exponential function the satiation process. Kinet-strategy; and (ii) situations where shepherds’ and

ics of intake were also modelled on fresh leafy animals’ strategies interact.

branches offered indoors to goats (Meuret, 1989) and can also be recorded at pasture by direct observation of feeding bouts. Rate of intake, especially at the

2. Feeding behaviour and control of intake beginning of the meal, seems to be a key factor for

understanding variations in voluntary intake between

Since the 1950s the feeding behaviour of rumin- forages (Moseley and Antuna Manendez, 1989)

ants fed indoors or at pasture has been extensively When fed indoors with two distributions and free

studied (see reviews by Jarrige et al., 1995; Ungar, access to forage, rumen fill, measured as the amount

1996). Intake is influenced primarily by hunger, of digesta in the rumen reaches a first maximum after

which is distressing, and by satiety, which is general- the morning main meal and the daily maximum after

ly pleasurable (Forbes, 1995). Regulation of feed the evening main meal (Baumont et al., 1988). In

intake and dietary choices combines short-term grazing sheep, Thomson et al. (1985) also observed

control of feeding behaviour related to the body a first maximum at 09:00 h and the daily maximum

(3)

capacity of the rumen is involved in the control of feeds allows anticipation of nutritional and

physio-intake is supported by two types of physiological logical consequences of intake. This is essential to

evidence: (i) stretch- and mechano-receptors are determine motivation to eat and feed preferences.

present in the rumen wall (Leek, 1977); and (ii)

increasing rumen fill with indigestible material by 2.2.1. Learning the post-ingestive effects of feeds

the equivalent of 1 kg dry digesta decreases intake The senses that are stimulated in the presence of

by 0.6 kg dry matter on average (review by Faverdin feed enable the animal to anticipate the postingestive

et al., 1995). When rumen fill is increased with effects of feed. The affective system integrates the

indigestible material, animals increase the number of taste of a feed with postingestive feedback and the

meals and the time spent ruminating per kg ingested cognitive system integrates the odour and appearance

(Baumont et al., 1990a). This stimulation of rumina- of the feed with its taste (Provenza et al., 1992).

tion behaviour, related to increased stimulation of Learned food aversions towards toxic plants or feeds

tactile receptors in the rumen wall, speeds up digesta experimentally laced with several compounds that

outflow and tends to reduce rumen fill. cause malaise have been clearly established in

During the main meals rapid fermentation of the ruminants (du Toit et al., 1991). Learned preferences

soluble fraction of feed increases osmotic pressure based on positive nutritional postingestive feedback

and VFA concentration of rumen fluid and lowers are undoubtedly also important for ruminants. After

pH (Remond et al., 1995). VFA infusion in the 10 days adaptation, lambs develop strong preferences

rumen decreases feed intake in the short term, more for non-nutritive flavours paired with glucose over

so as the molecular weight of the infused VFA is low flavours paired with saccharin (Burrit and Provenza,

(Faverdin et al., 1995). The influence of molecular 1992). Thus ruminants, like other mammals, develop

weight indicates involvement of osmotic pressure preferences for feeds that are richer in energy

(Carter and Grovum, 1990). Signals sensed by (Provenza, 1995). However, in a free-choice

situa-chemoreceptors in the rumen wall and / or in the liver tion, diet selection does not always maximise energy

enable the animal to avoid excess and nutritional density in the diet. Sheep eat some straw to prevent

disorders. This may explain the low duration of main rumen disorders, even when a more concentrated

meals with grass silages that contain large amounts feed is also on offer (Cooper et al., 1995). Sheep fed

of organic acids and ammonia, especially when they with a ‘long-fibre-free’ diet will eat 10-mm

poly-are poorly preserved (Van Os et al., 1995). In this ethylene fibre to restore normal rumination activity

case, satiation occurs before rumen fill reaches a (Campion and Leek, 1997). It was even observed

maximum. The same kind of adaptive phenomena that dairy goats could buffer seasonal variations in

may explain the choice of the feeds lowest in salt available vegetation composition. For example, at

when goats were given a diet rich in sodium chloride turn out, goats seek herbage species relatively low in

(Morand-Fehr et al., 1996). During a meal, the protein and rich in fibre; it is likely that animals

signals that contribute to the satiation process act select vegetation to reduce the variation in ingesta

simultaneously and probably additively as indicated composition as far as possible in the face of large

by the effects of an increase of rumen fill and an seasonal variations of vegetation composition

acetate infusion, performed separately or at the same (Fedele et al., 1993). Post-ingestive stimuli need to

time (Adams and Forbes, 1981). The different sig- be periodically reinforced, and so the animal has

nals that are sensed in the digestive tract and the regularly to re-evaluate the nutritional benefit of the

liver are integrated in the central nervous system and different choices.

balanced with other stimuli (Forbes, 1996). Dietary experience, particularly early in life,

modulates feeding behaviour and diet selection

2.2. Motivation to eat and feed preferences (Provenza, 1995). For example, naive sheep, cattle

and goats may graze up to 40% less than experienced

Satiation factors, mainly those related to rumen animals in the same environment (Provenza and

fill, have been favoured to explain forage intake. Balph, 1987). When grazing, animals adapt to their

(4)

plant species and their grazing skills (Flores et al., only 0.4 kg / day when they ate straw and received

1989), and by learning and memorising the dis- grass in the rumen but rose to 0.9 kg / day in the

tribution of resources (Dumont and Petit, 1998). reverse situation, although the digestibility of the

Learning from the dam and social partners is im- total diet was similar (Greenhalgh and Reid, 1971).

portant in the acquisition of dietary habits (Thor- Unpleasant sensations when previously eating straw

hallsdottir et al., 1990). Lambs accustomed to graze may explain its very low hedonic value. Hedonic

either clover or grass with their dam have a stronger behaviour can explain voluntary intakes greatly in

post-weaning preference for the species they had excess of requirements in wethers fed good quality

previously experienced (Ramos and Tennessen, forages (Baumont et al., 1997). The sensory

motiva-1992). After weaning, lambs reared by goats spent tion induced by a second distribution of fresh hay

less time eating clover than those reared by ewes, will override the satiety signals associated with the

consistent with the stronger preference for clover of first distribution (Baumont et al., 1990b). However,

ewes compared with goats (Orr et al., 1995). For the size of the second meal depends on the relative

adults, short-term neophilia may temporarily modu- quality of the two hays distributed. In goats, feed

late preferences. Sheep that had grazed either clover refusals may be explained by hedonic behaviour

or grass swards for 3 weeks subsequently showed a even when this selectivity prevents them meeting

stronger preference for the species previously lacking their energy requirements (Morand-Fehr et al.,

in their diet; nevertheless, after 3 days, they reverted 1991b). At pasture, the pleasant experiences

associ-to a stronger preference for the species they had been ated with the consumption of a new food have been

previously accustomed to eat (Parsons et al., 1994). suggested to explain preference for novelty or for

rarity (Newman et al., 1992). Hedonic behaviour,

2.2.2. Hedonic behaviour however, competes with the effort that has to be

Mechanisms of brain reward can to some extent expended to earn the reward. When animals have to

induce hedonic feeding behaviour, which competes walk to obtain a good forage, the preference for the

with physiological factors controlling intake. Sensory good forage depends on the amount offered the

properties of the feed will stimulate hedonic be- animals in reward (Dumont et al., 1998).

haviour to some extent. Total intake of sheep was In conclusion, Fig. 1 summarises the main

(5)

tionships between forage characteristics, short-term creases the amount of cell content, which is soluble,

control of intake, feeding behaviour and finally rapidly degraded and has almost no fill effect, and

forage intake. Modelling intake behaviour is a good increases the amount of cell walls. Consequently,

tool to test our knowledge of what controls intake. forage retention time in the rumen and thus fill effect

Forbes (1980) developed the first mechanistic model increases. In addition, tissue lignification increases

of intake in ruminants. More recently, Sauvant et al. the undegradable fraction of the cell walls and

(1996) proposed a mechanistic model of intake and decreases the degradation rate of the degradable

chewing activities that integrates relationships be- fraction (Grenet and Demarquilly, 1987). The time

tween feeding behaviour and digestive processes. needed to reduce particle size before ruminal escape

Decisions between eating, ruminating and resting are is also increased. Retention time in the rumen

taken according to the relative values of the func- depends mainly on the degradation rate of the

tions of motivation to eat and of satiety, which degradable fraction and on the proportion of the

integrate the signals described above. The forage is undegradable fraction, since its outflow rate does not

characterised by the cell wall content and its po- vary widely among plant species (Baumont et al.,

tential digestibility, and by the proportion of large 1997). Residence time of dry matter in the rumen is

particles. A palatability index and a coefficient of closely related to forage ingestibility (Baumont et al.,

heterogeneity take into account non-nutritional 1996).

characteristics and selection possibility in the forage

and are combined to estimate instantaneous 3.2. Sensory properties

palatability of the forage. This model accurately

predicted intake kinetics of sheep fed different types The sense of touch plays a role in the response of

of hay indoors. the animal to the feed (Arnold, 1966). Physical

characteristics of the forage such as dry matter content and particle size, and resistance to fracture

3. Role of plant characteristics on forage are known to affect ease of prehension and thus

ingestibility intake rate (Inoue et al., 1994). Sheep generally

prefer the feeds they can eat faster. With dried

Forage ingestibility is defined as the maximum forages, relative preferences for mixtures with

vary-quantity of the feed that can be eaten by the animal ing proportions of long and short particles were

when this is supplied ad libitum as the sole feed. closely related to the differences in intake rates

When given indoors, ingestibility of green forage (Kenney and Black, 1984).

depends mainly on its nutritive value and fill effect Small ruminants are also sensitive to the four

and on its sensory properties, assuming it does not primary tastes: sweet, salty, bitter and sour (Goatcher

contain toxic compounds (Fig. 1). Taking into and Church, 1970). However, animals’ response to

account the main variations in forage ingestibility added chemicals varies with feed management

allowed the development of the fill unit system to (Grovum and Chapman, 1988) and animals in the

predict feed intake for ruminants fed indoors (Jarrige same flock display a very wide range of response to

et al., 1986). the four taste components (Morand-Fehr et al.,

1993). The effects of various odoriferous compounds

3.1. Nutritive value and fill effect naturally present in plants were analysed by Arnold

et al. (1980) by sprinkling the chemicals onto cotton

For a given plant, ingestibility, like digestibility, is wool pads placed in the manger. Effects of

odorifer-dependent on the vegetation stage and the number of ous compounds are difficult to interpret because they

the vegetation cycle. During the first vegetation can vary in amplitude and sometimes in sign

accord-cycle, ingestibility decreases with the age of the ing to whether the animals are in choice situations or

plant (Demarquilly et al., 1981). The decrease in not. Moreover, several compounds recognised to

ingestibility with age of forage is the consequence of decrease intake by their odour or by their taste

the increase in its fill effect. As the plant ages, its (tannic acid, gramine, etc.) were found to decrease in

(6)

Low intake of silage is often attributed to low 1996). When an animal begins to eat, it selects a

palatability, since digestibility is only slightly differ- feeding site, and then a patch within that site.

ent from that of green forage. Effects of smell and

taste on silage intake were studied with anosmic and 4.1.1. Representation of the grazing process and

agustatory sheep (Michalet-Doreau, 1975). The in- theoretical bases of foraging behaviour

crease in silage intake by anosmic compared with Two approaches to foraging decisions have been

normal sheep was more pronounced with poorly proposed. Synthetic approaches assume animals

preserved (133%) than with well preserved silages organise their behaviour towards an objective,

(16.4%). Silage intake by agustatory sheep was not whereas analytical approaches assume that

behav-modified. Acetic acid added to the silage had a clear iours arise from cause–effect relationships. The basic

negative effect on intake (Buchanan-Smith, 1990). axiom of the main synthetic approach, Optimal

Amines are suspected to decrease palatability, be- Foraging Theory (OFT), is that present-day animals

cause in sheep initial eating rate at the beginning of forage optimally as a result of natural selection,

the meal was depressed by addition of amines in because optimal foraging enables the animal to

silage (Van Os et al., 1995). Low palatability of maximise its reproductive output (‘fitness’) (Krebs

silages probably results from learning the negative and McCleery, 1984). Fitness maximisation has

post-ingestive signals due to high amounts of fer- often been translated into efficiency of foraging,

mentation end products. which, for practical reasons, has often been equated

with short-term dry matter intake rate. The recent model of Newman et al. (1995) base foraging

4. Role of vegetation characteristics on grazing decisions on maximisation of fitness and include a

behaviour simplified mechanistic sub-model of digestion.

Analytical approaches explain foraging behaviour

Behavioural constraints are different and more in a complementary manner. For example, patch

diversified at pasture than indoor. Animals have to choice may be motivated by sensory stimuli, by

search for feed and they have to harvest the plants. post-ingestive feedback resulting from previous

Even so, animals are free at pasture to develop their choices, and by dietary experience. Synthetic and

own foraging strategy. They exploit environmental analytical approaches should be perceived as

com-heterogeneity by grazing selectively. Prediction of plementary rather than exclusive. Although OFT

intake and of the impact of animals on vegetation stresses the importance of natural selection in

de-needs an understanding of their foraging decisions. termining behaviour, it cannot exclude the

impor-When shepherds control their flocks on grazing tance of short-term dietary experiences.

Optimisa-circuit, their strategy of resource utilisation influ- tion-based predictions should, therefore, be

de-ences the animal’s behaviour and interacts with the veloped to include animals’ dietary experiences. The

foraging strategy of the flock. difficulty in dissociating the different approaches is

well illustrated by the question posed by Illius et al.

4.1. Foraging strategy and diet selection (1999): do animals eat a plant species faster because

they prefer it (sensory stimulus) or do they prefer it

On homogeneous swards, the importance of pre- because they can eat it faster (optimisation of

hension constraints first caused herbage intake to be behaviour)?

represented as the product of intake rate and grazing

time (Allden and Whittaker, 1970), assuming spatio- 4.1.2. How do vegetation characteristics influence

temporal stability of intake rate. As this approach is foraging decisions?

inappropriate on heterogeneous swards and

shrub-lands, a hierarchical approach is now preferred, that 4.1.2.1. Patch level

organises the grazing process into different levels A patch is defined as a spatial aggregation of bites

corresponding to animal decisions, which are then over which instantaneous intake rate (IIR) remains

integrated over wider spatio-temporal levels (Senft et relatively constant (Illius and Hodgson, 1996). Thus

(7)

paddock. IIR on the patch is determined by the mass the animal can graze the preferred patch without

of the bite and the functional relationship relating having to search for it, and (ii) those where

prefer-bite mass to the time required to handle it. Time per ences are modified by a cost of searching.

bite can be split into prehension and mastication When searching costs are negligible, animals

times. The animal is considered as subject to two generally prefer patches where they can eat rapidly

constraints: (i) the time required to prehend a bite, (Black and Kenney, 1984). However, preference is

which is independent of bite mass; and (ii) the time not absolute and intake rate is often less than

required to masticate the harvested material, which is predicted from optimisation theory. For example, on

proportional to bite mass (Newman et al., 1994; adjacent monocultures of grass and clover, the

Prache, 1997) and varies with plant species (New- proportion of clover in the diet of sheep is about

man et al., 1994). Bite mass is determined by the 70%, even though sheep generally eat clover faster

ease with which the sward can be gathered into the than grass (Newman et al., 1994). Why do animals

mouth and sheared (see review by Prache and express partial preference and choose mixed diets? In

Peyraud, 1997). On vegetative swards, sward height the short-term, the necessity for the animal to

and bulk density are the main determinants of bite consume the different patches to evaluate their

mass and IIR (Black and Kenney, 1984; Burlison et profitability, difficulty or lack of interest of the

al., 1991). On mature swards, bite mass is also animal in discriminating, and discrimination errors,

affected by the presence of ‘barrier’ components in have been proposed as explanations (Illius et al.,

the sward such as stems and dead material. Green 1999). On a daily scale basis, diurnal pattern in

leaf mass per unit area has been shown to be the best preferences, search for a balance of nutrients, avoid

predictor of bite mass and IIR across different excess of protein, and digestive constraints have

phenological stages of the sward (Penning et al., been proposed as explanations of partial preferences

1989; Prache et al., 1998). Sward height or green and mixed diets (Newman et al., 1995).

leaf mass do not take into account all the factors Preference is sensitive to relative vertical

availa-involved, because they are one- (sward height) or bility in different plant species. Animals may trade

two-dimensional (green leaf mass) descriptors, while off quality for quantity and switch to the less

bites are taken in three dimensions (Ungar, 1996). preferred item, when greater benefit is obtained on it

(Harvey and Orr, 1996; Prache et al., 1996). If one

4.1.2.2. Patch departure assumes that animals seek to maximise intake rate,

Forage depletion in the patch and expectation of the switch to the less preferred patch may be

intake opportunities in other patches will motivate predicted from potential intake rate on each patch.

the animal to move on. The animal has to make a For example, sheep rotationally grazing swards

trade-off between continuing to graze a patch where containing reproductive patches in a vegetative

back-it is experiencing diminishing marginal rewards, and ground, should consume the vegetative patches as

moving to another patch, thereby incurring a time long as their green leaf mass will allow a higher

cost. If the animal seeks to maximise intake rate, the intake rate than the reproductive ones (Fig. 2). Thus,

Marginal Value Theorem (MVT, Charnov, 1976) if animals seek to maximise intake rate, they should

predicts that the animal will leave the patch when switch to reproductive patches when the green leaf

intake rate within the patch equals the average intake mass on vegetative patches becomes lower than 300

rate for the whole environment. Demment et al. kg DM ha (i.e., 9 cm height in this study). This

(1993) and Laca et al. (1993) have globally validated result is in agreement with the preference

measure-MVT, but Bazely (1988) observed a longer residence ments of Dumont et al. (1995).

time than predicted by MVT. Searching constraints may limit intake rate. They

induce the animal to consume less preferred but

4.1.2.3. Multi patch level easier-to-reach food patches (Clarke et al., 1995) and

Vegetation characteristics, distance to water, need to develop search strategies: it may walk faster

for shelter, and social factors will then influence (Roguet et al., 1998), increase daily grazing time

patch choice. Considering vegetation characteristics, (Prache et al., 1998), or learn about the location of

(8)

quency to resources that had the same edible biomass relative to the distance to the patch (Dumont et al., 1998).

4.2. When a shepherd organises patch selection Shepherding consists in interacting with sponta-neous animal’s decisions. The herder’s interventions could be considered simply as new constraints to the expression of the behavioural trends of the flock. An experienced shepherd will identify spontaneous be-havioural trends and avoid countering them too often. While building a strategy for both animal feeding and resource management, the shepherd has to some extent to follow the movements of the flocks to maintain the confidence of the animals. Effective management can upgrade dietary motivation on heterogeneous pastures (Meuret, 1993a,b).

Fig. 2. Prediction of diet choices based on dry matter intake rate

Shepherding interacts with the animals’ foraging

maximisation: an example on swards containing reproductive

patches (dotted curve) in a background of vegetative patches (solid response patterns (Senft et al., 1987), through

trans-curve) (from Prache et al., 1998). _{humance and nomadism practices, that both have}

developed a wide range of informal and formal rules in seasonal forage uses. For animal nutrition

sci-cues (Edwards et al., 1997; Dumont and Petit, 1998). entists, there is now a need to devote more attention

The cost of searching is difficult to assess. Indirect to how a shepherd can manoeuvre an animal’s

indicators may be used, such as the animal’s degree appetite, taking full advantage of forage spatial

of selectivity expressed as the difference between heterogeneity and variability. That could help to

diet and sward composition, intake per distance reconsider the leader paradigm that ignores livestock

walked and proportion of potential bites encountered mobility characteristics and promotes settling process

removed (Prache et al., 1998; Roguet et al., 1998). A from land carrying-capacity evaluation (Scoones,

decrease in the horizontal availability may affect 1994).

encounter rate and therefore the proportion of pre- Rangelands are patchy environments. Within a

ferred species in the diet (Parsons et al., 1994). single day, a flock may well come across extremely

The effect of scale of patchiness may have marked diverse vegetation, and each of its members will

effects on animals’ foraging decisions, although it distribute thousands of bites over contrasted plant

has not, as yet, received much attention. Two types parts, from a tiny grass regrowth to a large mature

of patchiness may involve searching costs: small- leafy branch. Such broad diversity can motivate

scale, with constraints due to selection of preferred feeding. Firstly, it offers the animal many ways to

from less preferred food items, and larger scale with solve the usual conflicting problems: obtaining

maxi-constraints due to moving and locating alternative mal quality and adequate quantity (Owen-Smith and

patches. Fine mixtures reduce the opportunity for Novellie, 1981). Secondly, shrubs and leafy branches

selection. Sheep grazing grass / clover swards select can be easily prehended, allowing small ruminants

less clover when the species are offered in an high intake rate (Meuret, 1997). Finally, motivation

intimate mixture than in separate strips (Clark and is increased if the diversity of plant material on offer

Harris, 1985). Larger scale heterogeneity may im- during a grazing bout is high, especially when the

pose constraints on the visual perception of alter- material is of medium or low potential palatability

native patches and spatial memory. In an operant (Meuret and Bruchou, 1994).

(9)

succession of encounters of the different patches. A distinct roles during a circuit, and their use value for

model of shepherded circuit design, based on farm a specific phase during the meal is assessed

in-surveys together with intake kinetics analysis has dividually according to two simple criteria: the

been developed (Meuret, 1993a,b). The grazing relative abundance and the ‘instantaneous

palatabili-circuit may be viewed as an ordered sequence of ty’ (Sauvant et al., 1996) of the resources. A

patches offered during one main meal, the objective moderation-patch, with abundant but not highly

being to optimise the animal’s feeding motivation palatable plants, could be used at the beginning of

(Fig. 3). The ‘menu’ model is based on two rules: (i) the circuit to reduce the appetite of the flock. In

creation of synergetic sequences within the foraging contrast, an appetite promotion patch, with highly

bout; and (ii) follow spontaneous behavioural trends palatable but rare resources, has to be used at the

while developing flock’s confidence in shepherd’s beginning to stimulate a flock that has a low appetite.

interventions. When intake must be stimulated in a The target-patch, with medium plant abundance and

particular patch (‘target-patch’) with rough and less palatability, is then used as a main-course, for the

palatable resources (e.g., a patch to be cleared of bulk of the meal. When animals are losing interest in

scrub), the shepherd has to detect and mobilise this patch, a booster-patch (see Fig. 3) has to be used

complementary and sometimes contiguous patches in to add diversity and revive appetite. When the

the feeding site. The different patches could play booster-action is successful, another target-patch

Fig. 3. The Menu model: a shepherded grazing circuit is an ordered sequence of offered patches during one main meal, the objective being to constantly revive the animal’s motivation to eat on resources of medium or low quality (‘target-patches’). A booster patch can be of low plant abundance but high instantaneous palatability (Ba); or conversely of medium abundance and very low instantaneous palatability (Bb). In addition a booster action can be watering the flock or offering salt licks (from Meuret, 1993a,b).

(10)

with slightly better instantaneous palatability than the 5. Conclusions

main course-patch is used for a second course. At the

end, if the shepherd considers there is not enough From the different research fields reviewed in this

time for a new booster-course sequence, a dessert- paper (control of intake, determinants of forage

patch, with high plant abundance and palatability, ingestibility, feeding behaviour and diet selection at

can be used. pasture, shepherding practices) we can propose a

The organisation of a ‘menu’ by a shepherd, that framework for a mechanistic model of intake

be-takes full advantage of a patchy environment and haviour and patch choice at the feeding site level

emphasises the concept of instantaneous palatability, (Fig. 4). The balance between motivation to eat and

seems consistent with the role of aversions in diet satiation controls eating decision. The expression of

selection at pasture hypothesised by Provenza this eating decision, patch choice and intake rate,

(1996). This shows that the feed value of such an depends on the patch characteristics and among them

environment results largely from proper feeding mainly the potential intake rate and the spatial

management at the level of the feeding site and distribution.

feeding bout that could manoeuvre the appetite. Meal size and diet composition is mainly

con-Experienced shepherds observe their flock’s attitudes trolled by anticipation of postingestive effects to

to evaluate initial hunger, intermediate disaffection avoid nutritional excesses or deficiencies. The role

for food and signs of satiety. A shepherd who played by sensory properties of the diet

(‘palatabili-succeeds in designing a menu is able to generate a ty’) is still not completely understood as it is partly

‘build-up’ pastoral value from a heterogeneous and confounded with the role of nutritive value after

variable vegetation (Meuret, 1996). learning, but it is essential in explaining the control

Fig. 4. Framework of a mechanistic model of patch choice and intake behaviour within a feeding site. The animal representation is based on the model developed by Sauvant et al. (1996). The dotted line indicates the information that a shepherd can use to manage the grazing circuit.

(11)

of feeding behaviour. Ruminants generally develop reduce further decline in forage quality. Predicting

preferences for feeds that provide a high satiety level diet selection is further complicated in more complex

rapidly. Feeds that can be ingested fast and that are situations such as rangelands, with a large diversity

rapidly and highly digested are very palatable pro- on offer, making the environment more difficult for

vided they do not contain toxic compounds. Never- the animal to perceive, and offering it opportunities

theless, for a given nutritive value, sensory properties for trade-offs between behavioural options.

of the feed per se can stimulate or depress hedonic behaviour and thus intake. Offering choice to

ani-mals may stimulate forage intake level and so _References

forestall some pathological problems. The nutrient

requirements of each individual could be more Adams, G.B., Forbes, J.M., 1981. Additivity of effects of ruminal

precisely met. However, research is needed to de- acetate and either portal propionate or rumen distension on

food intake in sheep. Proc. Nutr. Soc. 40, 44A.

termine appropriate conditions for choice feeding.

Allden, W.G., Whittaker, A.M.C., 1970. The determinant of

A more efficient feed utilisation necessitates

im-herbage intake by grazing sheep: the interrelationship of factors

proved prediction of forage ingestibility. Residual _{influencing herbage intake and availability. Aust. J. Agric. Res.}

variation in predictive models of voluntary intake 21, 755–766.

based on nutritional characteristics (i.e., energy and Arnold, G.W., 1966. The special senses in grazing animals. 2.

Smell, taste and touch and dietary habits in sheep. Aust. J.

nitrogen values, fill effect) remains generally high.

Agric. Res. 17, 531–542.

Fill effect of forage can be expressed as its ruminal

Arnold, G.W., De Boer, G., Boundy, 1980. The influences of

retention time and can be predicted using in situ _{odour and taste on food preferences and food intake of sheep.}

degradability or laboratory methods. A so-called Aust. J. Agric. Res. 31, 571–585.

‘hedonic value’ of feed is probably much more Bailey, D.W., Gross, J.E., Laca, E.A., Rittenhouse, L.R.,

Coughenour, M.B., Swift, D.M., Sims, P.L., 1996. Mechanisms

difficult to predict, and to a first approximation can

that result in large herbivore grazing distribution patterns. J.

be assessed by the difference between observed and

Range Manage. 49, 386–400.

predicted intake. _{Baumont, R., Dulphy, J.P., Andrieu, J.P., 1988. Comportement}

At pasture, intake, diet composition and the impact alimentaire et etat de repletion du reticulo-rumen chez le´ ´ ´ ´

` ´

of grazing on the vegetation is the result of a mouton nourri a volonte de foin de prairie ou de luzerne avec

` ´ ˆ

acces en continu ou limite: incidences sur le controle physique

complex interaction between the animal and the

de l’ingestion. Reprod. Nutr. Dev. 28, 573–588.

vegetation. The livestock farmer has to organise this

Baumont, R., Brun, J.P., Dulphy, J.P., 1989. Influence of the

interaction within a pastoral strategy adapted to local _{nature of hay on its ingestibility and the kinetics of intake}

conditions. Through selective grazing, the animal during large meals in sheep and cow. In: Jarrige, R. (Ed.),

consumes a diet of a higher nutrient quality than that XVIth International Grassland Congress, Nice, France. French

Grassland Society, pp. 787–788.

on offer, and distributes its impact on the vegetation.

Baumont, R., Malbert, C.H., Ruckebusch, Y., 1990a. Mechanical

Nevertheless, the determinants of foraging decisions

stimulation of rumen fill and alimentary behaviour in sheep.

remain a matter of debate. In simple experimental _{Anim. Prod. 50, 123–128.}

situations (very short-term, simple dietary choices), Baumont, R., Seguier, N., Dulphy, J.P., 1990b. Rumen fill, forage

animals tend to maximise their rate of food intake. palatability and alimentary behaviour in sheep. J. Agric. Sci.

115, 277–284.

However, short-term prediction of foraging

behav-Baumont, R., Barlet, A., Jamot, J., 1996. L’effet d’encombrement

iour is not sufficiently validated on a daily scale

´ ´ ruminal des fourrages: sa relation avec l’ingestibilite et etude

basis, which may be affected by digestive con- _{de sa prevision au laboratoire. Renc. Rech. Ruminants 3,}_´

straints, balance of nutrients, diurnal pattern of diet 313–316.

selection, sampling, social effects within the flock, Baumont, R., Dulphy, J.P., Jailler, M., 1997. Dynamic of

vol-untary intake, feeding behaviour and rumen function in sheep

flock-farmer interactions. Prediction of total intake is

fed three contrasting types of hay. Ann. Zootech. 46, 231–244.

further impaired by the difficulty of predicting

Bazely, D.R., 1988. Foraging behaviour of sheep (Ovis aries L.)

grazing time. General understanding of diet selection _{grazing on swards of perennial ryegrass (Lolium perenne L.),}

may nevertheless be sufficient to predict switches PhD Thesis. Oxford University UK, 180 pp.

(12)

sheep. II. Height and density of pasture. Aust. J. Agric. Res. E., Farce, M.H., Theriez, M., Demarquilly, C. (Eds.), Proceed-35, 565–578. ings of the IVth International Symposium on the Nutrition of Buchanan-Smith, J.G., 1990. An investigation into palatability as Herbivores, Recent Developments in the Nutrition of

Herbi-a fHerbi-actor responsible for reduced intHerbi-ake intHerbi-ake of silHerbi-age by vores, INRA Editions, Paris, pp. 95–120.

sheep. Anim. Prod. 50, 253–260. Fedele, V., Pizillo, M., Claps, S., Morand-Fehr, P., Rubino, R., Burlison, A.J., Hodgson, J., Illius, A.W., 1991. Sward canopy 1993. Grazing behaviour and diet selection of goats on native structure and the bite dimensions and bite weight of grazing pasture in Southern Italy. Small Ruminant Res. 11, 305–322. sheep. Grass Forage Sci. 46, 29–38. Flores, E.R., Provenza, F.D., Balph, D.F., 1989. Role of ex-Burrit, E.A., Provenza, F.D., 1992. Lambs form preferences for perience in the development of foraging skills of lambs non-nutritive flavors paired with glucose. J. Anim. Sci. 70, browsing the shrub serviceberry. Appl. Anim. Behav. Sci. 23,

1133–1136. 271–278.

Campion, D.P., Leek, B.F., 1997. Investigation of a fibre appetite Forbes, J.M., 1980. A model of the short-term control of feeding in sheep fed a long fibre-free diet. Appl. Anim. Behav. Sci. 52, in the ruminant: effects of changing animal or feed

characteris-79–86. tics. Appetite 1, 21–41.

Carter, R.R., Grovum, W.L., 1990. A review of the physiological Forbes, J.M., 1995. In: Voluntary Food Intake and Diet Selection significance of hypertonic body fluids on feed intake and in Farm Animals, CAB International, Wallingford, UK, p. 532. ruminal function: salivation, motility and microbes. J. Anim. Forbes, J.M., 1996. Integration of regulatory signals controlling Sci. 68, 2811–2832. forage intake in ruminants. J. Anim. Sci. 74, 3029–3035. Charnov, E.L., 1976. Optimal foraging, the Marginal Value Goatcher, W.D., Church, D.C., 1970. Review of some nutritional

Theorem. Theor. Pop. Biol. 9, 129–136. aspects of the sense of taste. J. Anim. Sci. 31, 973–981. Clark, D.A., Harris, P.S., 1985. Composition of the diet of sheep Greenhalgh, J.F.D., Reid, G.W., 1971. Relative palatability to

grazing swards of differing white clover content and spatial sheep of straw, hay and dried grass. Br. J. Nutr. 26, 107–116. distribution. New Zealand J. Agric. Res. 28, 233–240. Grenet, E., Demarquilly, C., 1987. Rappels sur la digestion des

Clarke, J.L., Welch, D., Gordon, I.J., 1995. The influence of fourrages dans le rumen (parois) et ses consequences. In: ´

vegetation pattern on the grazing of heather moorland by red Demarquilly, C. (Ed.), Les Fourrages Secs: Recolte, Traite-deer and sheep. I. The location of animals on grass / heather ment, Utilisation, INRA Editions, Paris, pp. 141–162. mosaics. J. Appl. Ecol. 32, 166–176. Grovum, W.L., Chapman, H.W., 1988. Factors affecting the Cooper, S.D.B., Kyriasakis, I., Nolan, J.V., 1995. Diet selection in voluntary intake of food by sheep 4. The effect of additives sheep: the role of the rumen environment in the selection of a representing the primary tastes on sham intakes by diet from two feeds that differ in their energy density. Br. J. oesophageal-fistulated sheep. Br. J. Nutr. 59, 61–72. Nutr. 74, 39–54. Harvey, A., Orr, R.J., 1996. Dietary preference of sheep for grass

Demarquilly, C., Andrieu, J., Weiss, P., 1981. L’ingestibilite des and clover at contrasting sward surface heights. Br. Soc. Anim.

´ ´

fourages verts et des foins et sa prevision. In: Prevision de la Sci., Winter Meeting, 161.

Valeur Nutritive des Aliments des Ruminants, INRA Publi- Illius, A.W., Hodgson, J., 1996. Progress in understanding the cations, Versailles, pp. 155–157. ecology and management of grazing systems. In: Hodgson, J., Demment, M.W., Distel, R.A., Griggs, T.C., Laca, E.A., Deo, G.P., Illius, A.W. (Eds.), The Ecology and Management of Grazing 1993. Selective behaviour of cattle grazing ryegrass swards Systems, CAB International, Wallingford, UK, pp. 429–458. with horizontal heterogeneity in patch height and bulk density. Illius, A.W., Gordon, I.J., Elston, D.A., Milne, J.D., 1999. Diet In: Proc. of the XVII Int. Grass. Congress, pp. 712–714. selection in grazing ruminants: A test of rate maximization. du Toit, J.T., Provenza, F.D., Nastis, A.S., 1991. Conditioned food Ecology 80, 1008–1018.

aversions: How sick must a ruminant get before it detects Inoue, T., Brookes, I.M., John, A., Kolver, E.S., Barry, T.N., toxicity in foods? Appl. Anim. Behav. Sci. 30, 35–46. 1994. Effects of leaf shear breaking load on the feeding value Dumont, B., Petit, M., 1998. Spatial memory of sheep at pasture. of perennial ryegrass (Lolium perenne) for sheep. 2. Effects on Appl. Anim. Behav. Sci. 60, 43–53. feed intake, particle breakdown, rumen digesta outflow and Dumont, B., D’Hour, P., Petit, M., 1995. The usefulness of animal performance. J. Agric. Sci. 123, 137–147.

grazing tests for studying the ability of sheep and cattle to Jarrige, R., Demarquilly, C., Dulphy, J.P., Hoden, A., Robelin, J., exploit reproductive patches of pastures. Appl. Anim. Behav. Beranger, C., Geay, Y., Journet, M., Malterre, C., Micol, D., Sci. 45, 79–88. Petit, M., 1986. The INRA ‘fill unit’ system for predicting the Dumont, B., Dutronc, A., Petit, M., 1998. How readily will sheep voluntary intake of forage-based diets in ruminants: a review. J.

walk for a preferred forage ? J. Anim. Sci. 76, 965–971. Anim. Sci. 63, 1737–1758.

Edwards, G.R., Newman, J.A., Parsons, A.J., Krebs, J.R., 1997. Jarrige, R., Dulphy, J.P., Faverdin, P., Baumont, R., Demarquilly, ´

Use of cues by grazing animals to locate food patches: an C., 1995. Activites d’ingestion et de rumination. In: Jarrige, R., example with sheep. Appl. Anim. Behav. Sci. 51, 59–68. Ruckebusch, Y., Demarquilly, C., Farce, M.H., Journet, M.

´ `

Faverdin, P., 1985. Regulation de l’ingestion des vaches laitieres (Eds.), Nutrition des Ruminants Domestiques, INRA Editions,

´ `

en debut de lactation. These de Doctorat INA Paris-Grignon, Paris, pp. 123–181.

France, 131 pp. Kenney, P.A., Black, J.L., 1984. Factors affecting diet selection by Faverdin, P., Baumont, R., Ingvartsen, K.L., 1995. Control and sheep. I. Potential intake rate and acceptability of feed. Aust. J.

(13)

Krebs, J.R., McCleery, R.H., 1984. Optimization in behavioural Owen-Smith, N., Novellie, P., 1981. What should a clever ungulate ecology. In: Krebs, J.R., Davies, N.B. (Eds.), Behavioural eat? Am. Nat. 119, 151–178.

Ecology: An Evolutionary Approach, Sinauer Associates, Parsons, A.J., Newman, J.A., Penning, P.D., Harvey, A., Orr, R.J., Sunderland, MA, pp. 91–121. 1994. Diet preference of sheep: effects of recent diet, physio-Laca, E.A., Distel, R.A., Griggs, T.C., Deo, G., Demment, M.W., logical state and species abundance. J. Anim. Ecol. 63, 465–

1993. Test of optimal foraging with cattle: the marginal value 478.

theorem successfully predicts patch selection and utilisation. Penning, P.D., Parsons, A.J., Hooper, G.E., Orr, R.J., 1989. In: Proc. of the XVII Int. Grass. Congress, pp. 709–710. Responses in ingestive behaviour by sheep to changes in sward Laca, E.A., Ortega, I.M., 1995. Integrating foraging mechanisms structure. In: Jarrige, R. (Ed.), XVIth Int. Grass. Congress,

across spatial and temporal scales. In: Fifth Int. Rangeland Nice, France French Grassland Society, pp. 791–792. Congress, pp. 129–132. Prache, S., 1997. Intake rate, intake per bite and time per bite of Leek, B.F., 1977. Abdominal and pelvic visceral receptors. Br. lactating ewes on vegetative and reproductive swards. Appl.

Med. Bull. 33, 163–168. Anim. Behav. Sci. 52, 53–64.

´ ´ ˆ ´

Meuret, M., 1989. Valorisation par des caprins laitiers de rations Prache, S., Peyraud, J.L., 1997. Prehensibilite de l’herbe paturee ´ ´

ligneuses prelevees sur parcours: feuillages, fromages et flux chez les bovins et les ovins. INRA Prod. Anim. 10, 377–390.

´ ´ ` ´

ingeres. These de Doctorat en Sciences Agronomiques, Faculte Prache, S., Roguet, C., Louault, F., Petit, M., 1996. Evolution des

´ ´ ´ ´

des Sciences Agronomiques de Gembloux, 229 pp. choix alimentaires d’ovins entre talles vegetatives et epiees au

ˆ ´ ´

Meuret, M., 1993a. Piloter l’ingestion au paturage. Et. Rech. Syst. cours de l’exploitation d’un couvert epie de dactyle. Renc.

Agric. Dev. 27, 161–198. Rech. Ruminants 3, 89–92.

Meuret, M., 1993b. Les regles de l’Art: garder des troupeaux au Prache, S., Roguet, C., Petit, M., 1998. How degree of selectivity ˆ

paturage. Et. Rech. Syst. Agric. Dev. 27, 199–216. modifies foraging behaviour of dry ewes on reprodutive Meuret, M., 1996. Organizing a grazing route to motivate intake compared to vegetative sward structure. Appl. Anim. Behav.

on coarse resources. Ann. Zootech. 45 (Suppl.), 87–88. Sci. 57, 91–108.

´ ´

Meuret, M., 1997. Prehensibilite des aliments chez les petits Provenza, F.D., 1995. Role of learning in food preferences of ruminants en landes et sous-bois. INRA Prod. Anim. 10, ruminants: Greenhalgh and Reid revisited. In: Engelhardt, W.V., 391–401. Leonhard-Marek, S., Breves, G., Giesecke, D. (Eds.),

Proceed-´

Meuret, M., Bruchou, C., 1994. Modelisation de l’ingestion selon ings of the Eighth International Symposium on Ruminant

´ ´ ´ `

la diversite des choix alimentaires realises par la chevre au Physiology, Ruminant Physiology: Digestion, Metabolism, ˆ

paturage sur parcours. Renc. Rech. Ruminants 1, 225–228. Growth and Reproduction, Ferdinand Enke Verlag, Stuttgart, Michalet-Doreau, B., 1975. Recherches sur les causes des varia- pp. 233–247.

´ ´ ´

tions des quantites d’ensilage d’herbe ingerees par les rumin- Provenza, F.D., 1996. Acquired aversions as the basis for varied

` ´ ´

ants. These Docteur-Ingenieur Universite de Nancy, 99 pp. diets of ruminants foraging on rangelands. J. Anim. Sci. 74, Morand-Fehr, P., Ben Ayed, M., Hervieu, J., 1993. Individual 2010–2020.

responses of goats to main taste components included in feeds. Provenza, F.D., Balph, D.F., 1987. Diet learning by domestic In: Proceedings FAO-CIHEAM-EU Workshop. Aristotle Uni- ruminants: theory, evidence and practical implications. Appl. versity, Thessaloniki (Greece) 24–26 Sept. 1993, Sheep and Anim. Behav. Sci. 18, 211–232.

Goat Nutrition, pp. 41–45. Provenza, F.D., Pfister, J.A., Cheney, C.D., 1992. Mechanisms of Morand-Fehr, P., Ben Ayed, M., Hervieu, J., Lescoat, P., 1996. learning in diet selection with reference to phytotoxicosis in

Relationship between palatability and rate of intake in goats. herbivores. J. Range. Manage. 45, 36–45.

In: Lindberg, J.E., Gonda, H.L. (Eds.), Recent Advances in Ramos, A., Tennessen, T., 1992. Effect of previous grazing

´ ´

Small Ruminants Nutrition. Options Mediterraneennes, Vol. 34, experience on the grazing behaviour of lambs. Appl. Anim. CIHEAM, Paris, pp. 121–123. Behav. Sci. 33, 43–52.

´ `

Moseley, G., Antuna Manendez, A., 1989. Factors affecting the Remond, B., Brugere, H., Poncet, C., Baumont, R., 1995. Le ´

eating rate of forage feeds. In: Jarrige, R. (Ed.), XVIth Int. contenu du reticulo-rumen. In: Jarrige, R., Ruckebusch, Y., Grassl. Congress, Nice, France French Grassland Society, pp. Demarquilly, C., Farce, M.H., Journet, M. (Eds.), Nutrition des

789–790. Ruminants Domestiques, INRA Editions, Paris, pp. 253–298.

Newman, J.A., Parsons, A.J., Harvey, A., 1992. Not all sheep Roguet, C., Prache, S., Petit, M., 1998. Feeding station behaviour prefer clover: diet selection revisited. J. Agric. Sci. 119, 275– of ewes in response to forage availability and sward

phenologi-283. cal stage. Appl. Anim. Behav. Sci. 56, 187–201.

Newman, J.A., Parsons, A.J., Penning, P.D., 1994. A note on the Sauvant, D., Baumont, R., Faverdin, P., 1996. Development of a behavioural strategies used by grazing animals to alter their mechanistic model of intake and chewing activities of sheep. J. intake rates. Grass Forage Sci. 49, 502–505. Anim. Sci. 74, 2785–2802.

Newman, J.A., Parsons, A.J., Thornley, J.H.M., Penning, P.D., Scoones, I., 1994. In: Living With Uncertainty: New Directions in Krebs, J.R., 1995. Optimal diet selection by a generalist Pastoral Development in Africa, Intermediate Technology grazing herbivore. Functional Ecol. 9, 255–268. Publications, IIED, London.

Orr, R.J., Penning, P.D., Parsons, A.J., Harvey, A., Newman, J.A., Senft, R.L., Coughenour, M.B., Bailey, D.W., Rittenhouse, L.R., 1995. The role of learning and experience in the development Sala, O.E., Swift, D.M., 1987. Large herbivore foraging and of dietray choice by sheep and goats. Ann. Zootech. 44, 111. ecological hierarchies. BioScience 37, 789–799.

(14)

Thomson, B.C., Cruickschank, G.J., Poppi, D.P., Sykes, A.R., Ungar, E.D., 1996. Ingestive behaviour. In: Hodgson, J., Illius, 1985. Diurnal patterns of rumen fill in grazing sheep. Proc. A.W. (Eds.), The Ecology and Management of Grazing Sys-New Zealand Soc. Anim. Prod. 45, 117–120. tems, CAB International, Wallingford, UK, pp. 185–218. Thorhallsdottir, A.G., Provenza, F.D., Balph, D.F., 1990. Ability Van Os, M., Dulphy, J.P., Baumont, R., 1995. The effect of protein

of lambs to learn about novel foods while observing or degradation products in grass silages on feed intake and intake participating with social models. Appl. Anim. Behav. Sci. 25, behaviour in sheep. Br. J. Nutr. 73, 51–64.

(1)

succession of encounters of the different patches. A

distinct roles during a circuit, and their use value for

model of shepherded circuit design, based on farm

a specific phase during the meal is assessed

in-surveys together with intake kinetics analysis has

dividually according to two simple criteria: the

been developed (Meuret, 1993a,b). The grazing

relative abundance and the ‘instantaneous

palatabili-circuit may be viewed as an ordered sequence of

ty’ (Sauvant et al., 1996) of the resources. A

patches offered during one main meal, the objective

moderation-patch, with abundant but not highly

being to optimise the animal’s feeding motivation

palatable plants, could be used at the beginning of

(Fig. 3). The ‘menu’ model is based on two rules: (i)

the circuit to reduce the appetite of the flock. In

creation of synergetic sequences within the foraging

contrast, an appetite promotion patch, with highly

bout; and (ii) follow spontaneous behavioural trends

palatable but rare resources, has to be used at the

while developing flock’s confidence in shepherd’s

beginning to stimulate a flock that has a low appetite.

interventions. When intake must be stimulated in a

The target-patch, with medium plant abundance and

particular patch (‘target-patch’) with rough and less

palatability, is then used as a main-course, for the

palatable resources (e.g., a patch to be cleared of

bulk of the meal. When animals are losing interest in

scrub), the shepherd has to detect and mobilise

this patch, a booster-patch (see Fig. 3) has to be used

complementary and sometimes contiguous patches in

to add diversity and revive appetite. When the

the feeding site. The different patches could play

booster-action is successful, another target-patch

(2)

with slightly better instantaneous palatability than the

5. Conclusions

main course-patch is used for a second course. At the

end, if the shepherd considers there is not enough

From the different research fields reviewed in this

time for a new booster-course sequence, a dessert-

paper (control of intake, determinants of forage

patch, with high plant abundance and palatability,

ingestibility, feeding behaviour and diet selection at

can be used.

pasture, shepherding practices) we can propose a

The organisation of a ‘menu’ by a shepherd, that

framework for a mechanistic model of intake

be-takes full advantage of a patchy environment and

haviour and patch choice at the feeding site level

emphasises the concept of instantaneous palatability,

(Fig. 4). The balance between motivation to eat and

seems consistent with the role of aversions in diet

satiation controls eating decision. The expression of

selection at pasture hypothesised by Provenza

this eating decision, patch choice and intake rate,

(1996). This shows that the feed value of such an

depends on the patch characteristics and among them

environment results largely from proper feeding

mainly the potential intake rate and the spatial

management at the level of the feeding site and

distribution.

feeding bout that could manoeuvre the appetite.

Meal size and diet composition is mainly

con-Experienced shepherds observe their flock’s attitudes

trolled by anticipation of postingestive effects to

to evaluate initial hunger, intermediate disaffection

avoid nutritional excesses or deficiencies. The role

for food and signs of satiety. A shepherd who

played by sensory properties of the diet

(‘palatabili-succeeds in designing a menu is able to generate a

ty’) is still not completely understood as it is partly

‘build-up’ pastoral value from a heterogeneous and

confounded with the role of nutritive value after

variable vegetation (Meuret, 1996).

learning, but it is essential in explaining the control

(3)

of feeding behaviour. Ruminants generally develop

reduce further decline in forage quality. Predicting

preferences for feeds that provide a high satiety level

diet selection is further complicated in more complex

rapidly. Feeds that can be ingested fast and that are

situations such as rangelands, with a large diversity

rapidly and highly digested are very palatable pro-

on offer, making the environment more difficult for

vided they do not contain toxic compounds. Never-

the animal to perceive, and offering it opportunities

theless, for a given nutritive value, sensory properties

for trade-offs between behavioural options.

of the feed per se can stimulate or depress hedonic

behaviour and thus intake. Offering choice to

ani-mals may stimulate forage intake level and so

_References

forestall some pathological problems. The nutrient

requirements of each individual could be more

Adams, G.B., Forbes, J.M., 1981. Additivity of effects of ruminal

precisely met. However, research is needed to de-

acetate and either portal propionate or rumen distension on

food intake in sheep. Proc. Nutr. Soc. 40, 44A.

termine appropriate conditions for choice feeding.

Allden, W.G., Whittaker, A.M.C., 1970. The determinant of

A more efficient feed utilisation necessitates

im-herbage intake by grazing sheep: the interrelationship of factors

proved prediction of forage ingestibility. Residual

_{influencing herbage intake and availability. Aust. J. Agric. Res.}

variation in predictive models of voluntary intake

21, 755–766.

based on nutritional characteristics (i.e., energy and

Arnold, G.W., 1966. The special senses in grazing animals. 2. Smell, taste and touch and dietary habits in sheep. Aust. J.

nitrogen values, fill effect) remains generally high.

Agric. Res. 17, 531–542.

Fill effect of forage can be expressed as its ruminal

Arnold, G.W., De Boer, G., Boundy, 1980. The influences of

retention time and can be predicted using in situ

_{odour and taste on food preferences and food intake of sheep.}

degradability or laboratory methods. A so-called

Aust. J. Agric. Res. 31, 571–585.

‘hedonic value’ of feed is probably much more

Bailey, D.W., Gross, J.E., Laca, E.A., Rittenhouse, L.R., Coughenour, M.B., Swift, D.M., Sims, P.L., 1996. Mechanisms

difficult to predict, and to a first approximation can

that result in large herbivore grazing distribution patterns. J.

be assessed by the difference between observed and

Range Manage. 49, 386–400.

predicted intake.

_{Baumont, R., Dulphy, J.P., Andrieu, J.P., 1988. Comportement}

At pasture, intake, diet composition and the impact

alimentaire et etat de repletion du reticulo-rumen chez le´ ´ ´ ´

` ´

of grazing on the vegetation is the result of a

mouton nourri a volonte de foin de prairie ou de luzerne avec

` ´ ˆ

acces en continu ou limite: incidences sur le controle physique

complex interaction between the animal and the

de l’ingestion. Reprod. Nutr. Dev. 28, 573–588.

vegetation. The livestock farmer has to organise this

Baumont, R., Brun, J.P., Dulphy, J.P., 1989. Influence of the

interaction within a pastoral strategy adapted to local

_{nature of hay on its ingestibility and the kinetics of intake}

conditions. Through selective grazing, the animal

during large meals in sheep and cow. In: Jarrige, R. (Ed.),

consumes a diet of a higher nutrient quality than that

XVIth International Grassland Congress, Nice, France. French

Grassland Society, pp. 787–788.

on offer, and distributes its impact on the vegetation.

Baumont, R., Malbert, C.H., Ruckebusch, Y., 1990a. Mechanical

Nevertheless, the determinants of foraging decisions

stimulation of rumen fill and alimentary behaviour in sheep.

remain a matter of debate. In simple experimental

_{Anim. Prod. 50, 123–128.}

situations (very short-term, simple dietary choices),

Baumont, R., Seguier, N., Dulphy, J.P., 1990b. Rumen fill, forage

animals tend to maximise their rate of food intake.

palatability and alimentary behaviour in sheep. J. Agric. Sci.

115, 277–284.

However, short-term prediction of foraging

behav-Baumont, R., Barlet, A., Jamot, J., 1996. L’effet d’encombrement

iour is not sufficiently validated on a daily scale

´ ´ ruminal des fourrages: sa relation avec l’ingestibilite et etude

basis, which may be affected by digestive con-

_{de sa prevision au laboratoire. Renc. Rech. Ruminants 3,}_´

straints, balance of nutrients, diurnal pattern of diet

313–316.

selection, sampling, social effects within the flock,

Baumont, R., Dulphy, J.P., Jailler, M., 1997. Dynamic of vol-untary intake, feeding behaviour and rumen function in sheep

flock-farmer interactions. Prediction of total intake is

fed three contrasting types of hay. Ann. Zootech. 46, 231–244.

further impaired by the difficulty of predicting

Bazely, D.R., 1988. Foraging behaviour of sheep (Ovis aries L.)

grazing time. General understanding of diet selection

_{grazing on swards of perennial ryegrass (Lolium perenne L.),}

may nevertheless be sufficient to predict switches

PhD Thesis. Oxford University UK, 180 pp.

(4)

Herbi-a fHerbi-actor responsible for reduced intHerbi-ake intHerbi-ake of silHerbi-age by vores, INRA Editions, Paris, pp. 95–120.

1133–1136. 271–278.

characteris-79–86. tics. Appetite 1, 21–41.

Clarke, J.L., Welch, D., Gordon, I.J., 1995. The influence of fourrages dans le rumen (parois) et ses consequences. In: ´

Demarquilly, C., Andrieu, J., Weiss, P., 1981. L’ingestibilite des and clover at contrasting sward surface heights. Br. Soc. Anim.

´ ´

fourages verts et des foins et sa prevision. In: Prevision de la Sci., Winter Meeting, 161.

walk for a preferred forage ? J. Anim. Sci. 76, 965–971. Anim. Sci. 63, 1737–1758.

Edwards, G.R., Newman, J.A., Parsons, A.J., Krebs, J.R., 1997. Jarrige, R., Dulphy, J.P., Faverdin, P., Baumont, R., Demarquilly, ´

´ `

Faverdin, P., 1985. Regulation de l’ingestion des vaches laitieres (Eds.), Nutrition des Ruminants Domestiques, INRA Editions,

´ `

en debut de lactation. These de Doctorat INA Paris-Grignon, Paris, pp. 123–181.

(5)

1993. Test of optimal foraging with cattle: the marginal value 478.

Med. Bull. 33, 163–168. Anim. Behav. Sci. 52, 53–64.

´ ´ ˆ ´

Meuret, M., 1989. Valorisation par des caprins laitiers de rations Prache, S., Peyraud, J.L., 1997. Prehensibilite de l’herbe paturee ´ ´

ligneuses prelevees sur parcours: feuillages, fromages et flux chez les bovins et les ovins. INRA Prod. Anim. 10, 377–390.

´ ´ ` ´

ingeres. These de Doctorat en Sciences Agronomiques, Faculte Prache, S., Roguet, C., Louault, F., Petit, M., 1996. Evolution des

´ ´ ´ ´

des Sciences Agronomiques de Gembloux, 229 pp. choix alimentaires d’ovins entre talles vegetatives et epiees au

ˆ ´ ´

Meuret, M., 1993a. Piloter l’ingestion au paturage. Et. Rech. Syst. cours de l’exploitation d’un couvert epie de dactyle. Renc.

Agric. Dev. 27, 161–198. Rech. Ruminants 3, 89–92.

Meuret, M., 1993b. Les regles de l’Art: garder des troupeaux au Prache, S., Roguet, C., Petit, M., 1998. How degree of selectivity ˆ

on coarse resources. Ann. Zootech. 45 (Suppl.), 87–88. Sci. 57, 91–108.

´ ´

Proceed-´

Meuret, M., Bruchou, C., 1994. Modelisation de l’ingestion selon ings of the Eighth International Symposium on Ruminant

´ ´ ´ `

la diversite des choix alimentaires realises par la chevre au Physiology, Ruminant Physiology: Digestion, Metabolism, ˆ

paturage sur parcours. Renc. Rech. Ruminants 1, 225–228. Growth and Reproduction, Ferdinand Enke Verlag, Stuttgart, Michalet-Doreau, B., 1975. Recherches sur les causes des varia- pp. 233–247.

´ ´ ´

tions des quantites d’ensilage d’herbe ingerees par les rumin- Provenza, F.D., 1996. Acquired aversions as the basis for varied

` ´ ´

ants. These Docteur-Ingenieur Universite de Nancy, 99 pp. diets of ruminants foraging on rangelands. J. Anim. Sci. 74, Morand-Fehr, P., Ben Ayed, M., Hervieu, J., 1993. Individual 2010–2020.

Relationship between palatability and rate of intake in goats. herbivores. J. Range. Manage. 45, 36–45.

In: Lindberg, J.E., Gonda, H.L. (Eds.), Recent Advances in Ramos, A., Tennessen, T., 1992. Effect of previous grazing

´ ´

Small Ruminants Nutrition. Options Mediterraneennes, Vol. 34, experience on the grazing behaviour of lambs. Appl. Anim. CIHEAM, Paris, pp. 121–123. Behav. Sci. 33, 43–52.

´ `

Moseley, G., Antuna Manendez, A., 1989. Factors affecting the Remond, B., Brugere, H., Poncet, C., Baumont, R., 1995. Le ´

789–790. Ruminants Domestiques, INRA Editions, Paris, pp. 253–298.

phenologi-283. cal stage. Appl. Anim. Behav. Sci. 56, 187–201.

(6)