Effect of vasoactive intestinal polypeptide and environmental temperatures on feed intake, digesta flow and nutrient digestion in sheep

Abstract

Three experiments were conducted to test the hypothesis that vasoactive intestinal polypeptide (VIP) infused into the gastric artery and exposure to a low temperature will increase feed intake, duodenal flow and amino acid supply to the small intestine of sheep, both effects as a result of increased ruminal outflow. A total of eight sheep (55 ± 2.7 kg) with rumen and duodenal cannulae and eight sheep without digestive cannulae were provided with continuous access to a diet of alfalfa pellets. Water and salt licks were accessible 24 h d-1. Two infusion treatments, VIP (1 nmol min-1) solution or a saline control (0.9% NaCl solution) were given through a left gastric-artery catheter for 10 min each hour for the first 3 h after feeding each day for 3 to 4 consecutive days in a crossover arrangement during experimental periods. Sheep were exposed to 1 ± 2°C in exp.1, to a thermoneutral (21 ± 2°C) environment in exp. 3 and to both thermoneutral (21 ± 1.5°C) and cold environments (1 ± 2°C) in exp. 2. These studies demonstrated that a VIP infusion of short duration did not increase dry matter intake (DMI) (P > 0.05) and did not influence duodenal passage of DM, OM, CP, amino acids (AA) or bacterial protein (P > 0.05). The exposure of animals to a cold environment stimulated (P < 0.05) intake of DM, OM and AA and duodenal passage of DM, OM, AA and microbial protein. There was an interaction (P < 0.05) between VIP and environmental temperature such that VIP improved duodenal AA passage in the thermoneutral, but not in the cold, environment. The data suggest that short-term VIP treatment does not induce a change in feed intake when sheep have access to feed for 24 h d-1. Cold environmental temperature stimulates significant increases in feed intake and passage of protein and AA into the small intestine of sheep fed ad libitum, such that there was enrichment of intestinal supply of AA relative to digestible organic matter. Key words: Sheep, vasoactive intestinal peptide, feed intake, environmental temperature