Effect of vasoactive intestinal polypeptide infusion on feed intake, digesta flow and nutrient digestion in sheep with access to feed for limited time

Abstract

Two experiments were conducted to test the hypothesis that vasoactive intestinal polypeptide (VIP) infusion into the gastric artery increases feed intake, duodenal flow and amino acid supply to the small intestine of sheep. Four sheep in exp. 1 and five sheep in exp. 2 were fistulated with rumen and duodenal cannulae. Sheep in exp. 2 also had an ileal cannula. In both experiments animals were fed a diet of alfalfa pellets ad libitum for 8 h per day in a thermoneutral environment (20 ± 2 °C) and had free access to water and mineralized salt blocks. In exp. 1, VIP was infused at 1 nmol min−1 through a gastric-artery catheter for 10 min duration each hour for 3 h each day for 4 consecutive days. In exp. 2, VIP was infused at 1.5 nmol min−1 for 10 min duration each half-hour for 3 h each day for 7 consecutive days. Control sheep were infused with saline. Vasoactive intestinal polypeptide infusion increased (P < 0.05) feed intake by 14.3 and 26.1% in exp. 1 and exp. 2, respectively. In exp. 2, there was a positive regression (P < 0.01) between intake and duodenal passage of dry matter (DM) (n = 5, r2 = 0.67), organic matter (OM) (n = 5, r2 = 0.68), and amino acids (AA) (n = 5, r2 = 0.85). The present results suggest that VIP may play a role as a physiological regulator of feed intake in sheep and also has potential to increase the supply of nutrients to the animal. Key words: Digesta passage, intake, sheep, vasoactive intestinal polypeptide