Factors affecting the voluntary intake of food by sheep

Abstract

1. Sheep given ground and pelleted lucerne hay (Medicago sativa)ad lib.were infused intravenously with pentagastrin, secretin, cholecystokinin (CCK) and its analogues to assess their effects on motility of the reticulo-rumen and on food intake. In the latter experiments the animals were deprived of their diet for periods of up to 6 h to induce hunger and the infusions were made before and during 3–10 min periods of feeding.2. Pentagastrin, an analogue of gastrin, depressed intake by 35–50% (P< 0.05) when it was infused at 9 μg/kg per h during 30 min of feeding. The threshold may however be below 1 μg/kg per h as this dose decreased intake of 12–17%. The frequency of reticular contractions decreased by 13, 35, 39 and 44% when 1, 3, 9 and 27 μg pentagastrin/kg per h respectively was infused (P> 0.025).3. Secretin depressed food intake 38% after 30 min (P> 0.025) when 8 Clinical Units (CU)/kg per h was infused but the threshold could be less than this dose since 0.5 CU/kg per h depressed intake by 12%. Contraction amplitude but not frequency decreased at 8 CU/kg per h.4. CCK produced a 39% decrease in intake during the first 10 min of feeding (P< 0.05) and the threshold was between 5 and 15 Ivy Dog Units (IDU) or 425 and 1276 pmol/kg per h. The frequency of reticular contractions was not affected by 1.7 IDU/kg per h but it was depressed 21 and 63% by 5 and 15 IDU/kg per h. Octapeptide at 1.5 and 3 μg (1312 and 2624 pmol)/kg per h depressed intake by 11 and 43% respectively after 10 min (not significant) and 1.5 μg/kg per h depressed motility by 39% (P< 0.01). Ceruletide at 810 ng (599 pmol)/kg per h depressed intake by 31% (not significant) after 10 min and decreased motility by 52% (P> 0.05). The threshold dose for ceruletide on intake appeared to be about 90 ng or 66 pmol/kg per h which is considerably less than that for CCK or octapeptide.5. The biological significance of gastrointestinal hormones as signals of satiety in normal sheep is not known since doses of pentagastrin and CCK that suppressed intake also interfered quite markedly with motility. However there is good reason to suspect that elevated concentrations of gastrin and CCK in blood of parasitized sheep may account at least in part for their symptoms of rumen atony and reduced food intakes.