The fasting metabolism of adult wether sheep.

Abstract

The heat produced when an animal is fasted in an environment which is neither too hot nor too cold to cause increases in metabolism is a measure of the energy needed to maintain that animal. When man is the subject, muscular repose can invariably be assured and the measurement of heat production is termed the basal metabolism. Most animals do not co-operate in the way that man does and their heat production during fasting thus includes some heat incidental to normal body movement. The measurement is, therefore, best termed the fasting metabolism. Many thousands of determinations of the basal metabolism of man have been made and have recently been reviewed in detail by Quenouille, Boyne, Fisher & Leitch (1951). No studies on any similar scale have been made of the fasting metabolism of sheep, though notable investigations have been made by Ritzman & Benedict (1930, 1931), Lines & Pierce (1931) and Marston (1948). In addition, Brody (1945) has made a number of determinations of heat production in sheep at various times after food. During the past 7 years, the fasting metabolism of adult wether sheep has been determined in this laboratory on many occasions during the course of other experiments and this paper is concerned with analysis of the results. EXPERIMENTAL Animals. The sheep used were all castrated males. The breeds were Scottish Blackface, Cheviot and Down crosses. Before experiments began the sheep were trained to become accustomed to the apparatus. Graham (1958) showed that, when untrained sheep were fasted, heat production was 20 yo higher than it was in the same individuals 3 weeks later after they had been accustomed to confinement. Method of determination of fasting metabolism. A standard method was used. The sheep was given a ration of hay or dried grass, calculated to be sufficient to prevent its losing or gaining weight, for at least 7 days before the determination of fasting heat production began. This procedure was adopted because Marston (1948) showed that the level of feeding of sheep before a fast had a marked effect on the length of time it took to reach a minimal metabolism. The sheep was given its last meal at 5 p.m. and metabolism determinations were commenced at 9 a.m. the following morning and were continued until 9 a.m. 4 days later. The total length of fast was thus I 12 h. All sheep had access to unlimited water though they consumed little. On each of the 4 days of the experiment, oxygen consumption, carbon dioxide production, methane production and excretion of nitrogen in the urine were measured. The sheep was