Factors limiting the intake of feed by the sheep. VI. Feed intake in the ruminant lamb in relation to the administration of a nutrient solution per abomasum

The voluntary consumption by lambs of a ground and pelleted diet containing 24.4% crude protein on a dry matter basis was studied over 25 days when a nutrient solution based on evaporated cows' milk and lactose was administered per abomasum. The lambs, initially 11-12 weeks old and weighing 26 kg, had been surgically prepared with permanent abomasal fistulae. Separate digestion experiments were conducted to determine (i) the digestible energy (DE) content of the basal diet and (ii) patterns of digestion of the basal diet in the stomach and intestines. The basal diet had a DE content of 3.39 kcal/g dry matter and provided 22 g crude protein digested in the intestines per 100 g digestible organic matter; the nutrient solution contained 7.2 g nitrogen/Mcal gross energy and the energy was 94% digestible. In the digestion experiments, the rates of flow of digesta from the rumen and abomasum were 9.9 and 14.4 l/day respectively; the ruminal digesta was at pH 5.7 and the concentration of volatile fatty acids was 138 mmoles/litre. Approximately 59% of the apparent digestion of organic matter and 78% of the digestion of acid detergent fibre occurred in the stomach. The supplemented and unsupplemented groups of lambs consumed similar amounts of feed in a control period; the daily intakes expressed in relation to body weight in kg0.75 (BWkg0.75) were 101 g dry matter and 341 kcal DE. When nutrient solution providing 836 kcal gross energy or 58 kcal DE/BWkg0.75 per day was administered per abomasum, voluntary feed consumption declined by 16 g dry matter/BWkg0.75 or 53 kcal DE/BWkg0.75. Thus on the basis of DE, the decline in dietary intake compensated for the nutrient solution administration to the extent of 91 %. The daily DE intake of the supplemented group during nutrient administration was 345 kcal/BWkg0.75 and the rate of body height increase was 306 g/day ; the corresponding values for the unsupplemented group were 340 kcal DE/BWkg0.75 and 290 g/day. The data indicated that caloric homeostasis was well developed in lambs of this maturity and that the diet probably contained sufficient essential nutrients to permit the lambs to exhibit maximum growth. The capacity of the lamb to consume feed and increase in body weight did not appear to be restricted by any feature of ruminal digestion.