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

Abstract

Understanding what determines feeding behaviour in herbivores is essential to optimise the use of forages in breeding systems. Herbivores can evaluate foods by associative learning of their pre-ingestive characteristics (taste, odour, etc.) and their postingestive consequences. Post-ingestive consequences are acknowledged as influencing intake and food choices, but the role of pre-ingestive characteristics is still being debated. Our experiment was designed to test their separate effects on daily dry matter intake (DMI), intake patterns and short-term choices in sheep by crossing the nature of the hay orally consumed (o) ad libitum, lucerne (L) or grass (G), with the nature of the hay introduced into the rumen (r), L or G, at a rate of half the total amount of hay received the day before. We applied four treatments, Go/Gr, Go/Lr, Lo/Gr and Lo/Lr, to test the effects of (i) post-ingestive consequences with similar pre-ingestive characteristics (Go/Gr v. Go/Lr; Lo/Gr v. Lo/Lr) and (ii) pre-ingestive characteristics with similar post-ingestive consequences at the end of the feeding period (Go/Lr v. Lo/Gr). Six rumen-fistulated sheep underwent all the treatments over 11-day periods in a latin square design. Eating time was restricted to 6 h/day, intraruminal introductions were performed just before food offer and choice tests were conducted after food removal. For similar pre-ingestive characteristics, DMI increased when L hay was introduced into the rumen rather than G ( P , 0.05), possibly owing to a lower fill effect of L due to its lower NDF content and higher rumen degradability. The increased DMI resulted from longer eating time when G was orally consumed (149 v. 192 min, P , 0.05), whereas it resulted from higher intake rate with L (4.8 v. 6.1 g/min, P , 0.05). For similar post-ingestive consequences at the end of the feeding period (Go/Lr and Lo/Gr), DMI were similar ( P . 0.05). Pre-ingestive characteristics or palatability per se did not therefore influence daily intake, although they influenced eating patterns. Pre-ingestive characteristics also greatly influenced short-term choices in favour of the hay that was not previously consumed, independently of any post-ingestive influence. This study confirms the effects of post-ingestive consequences on daily intake, but demonstrates that these variations are obtained by different behavioural adjustments under the influence of pre-ingestive characteristics. Preference for novelty, regardless of post-ingestive consequences, thus suggests that sheep may seek a diverse diet more for pleasure than for functional purposes, with implications for animal welfare.Keywords: feeding behaviour, intake, sensory characteristics, rumen, sheep ImplicationsBreeding systems tend to increase the proportion of forages in the total diet of ruminants, both for economic gain and in response to social demand for environmental protection and welfare. However, their use remains to be optimised. To do this we need a better understanding of how food characteristics influence feeding beh...

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

“…Does the palatability of food sensory characteristics affect intake and feeding pattern? Using two good-quality forages (lucerne and grass hays) with different sensory characteristics, daily dry matter intake did not differ when controlling for post-ingestive consequences (Favreau et al, 2010c; Figure 1). Greenhalgh and Reid (1971) found similar results when offering two good-quality forages (dried grass and meadow hay), whereas they demonstrated that sensory characteristics influenced the daily intake of a lowquality forage (oat straw) compared with a good-quality forage (dried grass; Figure 1).…”

“…This can be achieved by (i) measuring short-term preferences and/or intake since it can be assumed that the postingestive consequences of the food have not been felt by the animal yet (Favreau et al, 2010c), (ii) by using an ingredient able to modify the sensory properties of the food without adding any post-ingestive consequence (e.g. a calorie-free sweetener such as saccharin; Hellekant et al, 1994), (iii) by offering the different food items simultaneously since it increases the difficulty for the animal to identify which food item is responsible for which consequence (Duncan and Young, 2002;Favreau et al, 2010b), and/or (iv) by checking, with a conditioning procedure, that the intake of the added sensory modifier does not cause any post-ingestive consequence at the dose rate involved in the study (Gherardi and Black, 1991;Favreau et al, 2010a).…”

“…The palatability of the two tested food (A and B) could then be assessed by comparing feeding behaviour in reversed situations (i.e. comparison of Ao/Br and Bo/Ar situations), where the food sensory characteristics are different, but the diet composition and the post-ingestive consequences are similar (Greenhalgh and Reid, 1971;Favreau et al, 2010c).…”

“…In the same way, moderate energy preloads, combined with manipulations of palatability during a test meal, resulted in overconsumption in humans, thus demonstrating that the hedonic value of food sensory characteristics decreased the ability of short-term satiety cues to stop intake (Yeomans et al, 2001). In sheep, when post-ingestive consequences were controlled, the intake of lucerne hay was higher than that of grass hay just after food distribution, indicating that the motivation to eat was then higher than the negative fill effect of the hay introduced in the rumen (Favreau et al, 2010c). Finally, the physical form (pellets or cubes) and the addition of monosodium glutamate (i.e.…”

“…The first experiment (Greenhalgh and Reid, 1971) used a good-quality forage (dried grass 5 Dg, 13.9% of CP in dry matter) and a low-quality forage (oat straw 5 Os, 3.9% CP). The second (Greenhalgh and Reid, 1971) and third (Favreau et al, 2010c) experiments used two good-quality forages (meadow hay 5 Mh, 7.7% CP v. dried grass 5 Dg, 13.9% CP; lucerne hay 5 Lh, 15.6% CP v. grass hay 5 Gh, 7.2% CP, respectively). the literature concerning sweet taste (see Ginane et al, 2011 for review).…”