Rumen fill, forage palatability and alimentary behaviour in sheep

Abstract

S U M M A R YFive sheep were fitted with rumen cannulas and fed once daily ad libitum at 09.00 h with a low-quality mixed-grass hay or a good-quality lucerne hay. The effects of a second amount of the same hay or of the second hay distributed at the end of the large meal following the morning distribution, when rumen fill reaches its daily maximum, were investigated for feed intake, alimentary behaviour and rumen fill. The second distribution induced a true meal (200-400 g dry matter intake), except in the case of mixed grass offered after lucerne. On the basis of initial eating rate and the amount ingested, the highest palatability was for lucerne offered after mixed grass, and the lowest for mixed grass offered after lucerne. Diet selection was more pronounced with lucerne than with mixed grass, as indicated by the larger decrease in the neutral detergent fibre content of the fraction ingested. The true meals following the second distribution were associated with an increase in rumen fill up to 10% of the daily maximum observed without the second distribution. However, rumen fill with lucerne remained 1 kg lower than with mixed-grass hay, even after a second meal. It is concluded that the sensory response induced by a distribution of a sufficiently palatable hay is able to override the satiety signals due to rumen fill, and that there is a permanent balance between the stimuli related to the characteristics of the food available and those related to reticulo-ruminal digesta.

Feeding behaviour of sheep fed lucerne v. grass hays with controlled post-ingestive consequences

“…Despite this high proportion, sheep showed good adaptability, as they decreased their voluntary daily intake accordingly and stabilized it within 3 days. Sheep in treatments Lo/Lr and Go/Gr consumed an amount of hay such that they received similar total amounts as sheep orally fed lucerne or grass hay ad libitum with no time restriction (Baumont et al, 1990a). Our results are thus consistent with previous studies in which addition of 1 g of feed into the rumen lowered voluntary intake by about 0.9 g (Faverdin et al, 1995 for review).…”

“…Palatability can be considered to reflect those characteristics of a food which invoked a sensory response in the animal (Greenhalgh and Reid, 1971;Baumont, 1996). For instance, the sensory motivation induced by offering a fresh meal of a palatable hay in satiated sheep could override satiety signals and induced a new meal (Baumont et al, 1990a). However, the food learning theory considers that palatability and post-ingestive consequences are interrelated , because ruminants can learn to associate the pre-ingestive characteristics of a food with its post-ingestive consequences and adjust their choices accordingly (Forbes and Provenza, 2000).…”

Food sensory characteristics: their unconsidered roles in the feeding behaviour of domestic ruminants

“…It has been shown that satiated sheep ate a substantial meal after a second distribution of a sufficiently palatable hay; this meal was then associated with an increase in rumen fill of up to 10% of the daily maximum observed without this second distribution (Baumont et al, 1990b). The hedonic stimulation induced by the new distribution thus overrode the satiety signals due to rumen fill.…”

Palatability and feeding behaviour in ruminants. A review

“…The sensory response induced by a second distribution of fresh hay will override the satiety signals induced by the meal following the first distribution (Gatel, 1984). However, the size of the second meal depends on the relative palatability of the two hays distributed (Baumont et al, 1990). Sheep satiated with low-quality meadow hay will eat 400 g of lucerne hay (fig 1 however, Hedonic behaviour also competes with the effort that has to be expended to earn the reward.…”