Postingestive Feedback from Starch Influences the Ingestive Behaviour of Sheep Consuming Wheat Straw
Applied Animal Behaviour Science
Villalba, J. and Provenza, F. (2000). Postingestive feedback from starch influences the ingestive behaviour of sheep consuming wheat straw. Applied Animal Behaviour Science, 66(1-2), 49-63. doi:10.1016/S0168-1591(99)00081-7
Plant species present a complex array of biochemicals to herbivores that in conjunction with a plant's physical structure influence intake. Our objective was to determine the role of postingestive feedback from macronutrients on the ingestion of a low-quality forage by sheep (Ovis aries). We compared the ingestive behaviour of two groups of lambs conditioned with intraruminal infusions of starch (100 g/lamb/day; Group 1) or water (250 ml/lamb/day; Group 2) while they grazed wheat straw (held erect in wooden frames; 30 cm height; Trials 1, 2 and 3) or consumed wheat straw from food boxes (1–2 cm particle size; Trial 4). Lambs were conditioned as individuals during Trials 1 and 4, in pairs during Trial 2, and as two groups (Groups 1 and 2) during Trial 3. Ingestive behaviour – intake, intake rate, number of bites, bite size, bite rate — was assessed during individual tests that lasted 5 min/lamb. After conditioning and testing, all animals had restricted access (80% of their daily energy requirements) to a basal diet of alfalfa pellets. No differences between groups were detected during initial tests (before infusing starch) or during Trial 1 (P>0.05). Lambs conditioned with starch in Trial 2 consumed more straw (8 vs. 2 g; P<0.05) at higher rates (2.3 vs. 1.0 g/min; P<0.1), and took more (13 vs. 5; P<0.1) and larger (0.59 vs. 0.31 g/bite; P<0.05) bites than lambs conditioned with water. This pattern was maintained during Trial 3: Lambs infused with starch showed higher intake (24 vs. 5 g; P<0.01), intake rate (5.4 vs. 1.4 g/min; P<0.001), bites (29 vs. 10; P<0.01), bite rate (6.7 vs. 2.6 bites/min; P<0.01) and bite size (0.86 vs. 0.54 g/bite; P<0.05) than lambs infused with water. In Trial 4, lambs conditioned with starch consumed more straw (21 vs. 9 g; P<0.1), at higher rates (5.4 vs. 2.6 g/min; P<0.1), than lambs conditioned with water. Thus, the postingestive effects of energy played an important role in modulating rates of food intake, and our findings suggest postingestive feedback from macronutrients is a fundamental factor influencing the ingestive behaviour of herbivores.