Postingestive feedback from starch influences the ingestive behaviour of sheep consuming wheat straw

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 postingesŽ . tive feedback from macronutrients on the ingestion of a low-quality forage by sheep OÕis aries . We compared the ingestive behaviour of two groups of lambs conditioned with intraruminal Ž . Ž . infusions of starch 100 grlambrday; Group 1 or water 250 mlrlambrday; Group 2 while they Ž . grazed wheat straw held erect in wooden frames; 30 cm height; Trials 1, 2 and 3 or consumed Ž . wheat straw from food boxes 1–2 cm particle size; Trial 4 . Lambs were conditioned as Ž . 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 minrlamb. After conditioning and testing, all Ž . animals had restricted access 80% of their daily energy requirements to a basal diet of alfalfa Ž . pellets. No differences between groups were detected during initial tests before infusing starch or Ž . Ž during Trial 1 P)0.05 . Lambs conditioned with starch in Trial 2 consumed more straw 8 vs. 2 . Ž . Ž . g; P-0.05 at higher rates 2.3 vs. 1.0 grmin; P-0.1 , and took more 13 vs. 5; P-0.1 and Ž . larger 0.59 vs. 0.31 grbite; P-0.05 bites than lambs conditioned with water. This pattern was Ž . maintained during Trial 3: Lambs infused with starch showed higher intake 24 vs. 5 g; P-0.01 , Ž . Ž . Ž intake rate 5.4 vs. 1.4 grmin; P-0.001 , bites 29 vs. 10; P-0.01 , bite rate 6.7 vs. 2.6 . Ž . bitesrmin; P-0.01 and bite size 0.86 vs. 0.54 grbite; P-0.05 than lambs infused with Ž . water. In Trial 4, lambs conditioned with starch consumed more straw 21 vs. 9 g; P-0.1 , at Ž . higher rates 5.4 vs. 2.6 grmin; P-0.1 , than lambs conditioned with water. Thus, the ) Corresponding author. Tel.: q1-435-797-2539; fax: q1-435-797-3796; e-mail: [email protected] 0168-1591r00r$ see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0168-1591 99 00081-7 ( ) J.J. Villalba, F.D. ProÕenzarApplied Animal BehaÕiour Science 66 2000 49–63 50 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. q 2000 Elsevier Science B.V. All rights reserved.