Effects of long-term ad libitum feeding on the voluntary food intake, body weight, body composition and adipose tissue morphology of lean adult sheep.

An experiment was conducted in which adult Suffolk ewes were given an ad libitum diet for 9 months and then compared with control sheep fed a maintenance diet. The changes in body weight and food intake could be divided into three phases. In the first phase, a high food intake 3-3.5 times the maintenance level corresponded to a high body weight gain of more than 200 g/day. In the second phase, body weight also increased, but voluntary food intake decreased. In the last phase, a stable body weight was associated with a decreased food intake. More than 6 months elapsed before this stability was reached. After a prephase, characterized by a large increase of body water, ad libitum feeding induced fat deposition with a consequent increment in body fat from 9 to 37 p. 100 of live weight. The total amounts of body water, mineral matter and protein remained stable but their relative amounts (in percent of live weight) decreased. The body weight of each sheep stabilized at a determined level of body fat (25-50 kg) ; the relative amounts were less variable (35-42 p. 100 of live weight). During the first 18 weeks of ab libitum feeding, both control and experimental sheep achieved the same mean fat cell weight (0.14 !g). Between the 18th and 22nd week a rapid increase was observed in the experimental sheep (mean + SD : 0.37 + 0.15 Ag), followed by stable values until the end of the test. The unimodal adipocyte size frequency distribution remained unaffected in the control group ; the adipocytes of the experimental group shifted towards a bimodal distribution, showing an increase in the proportion of small cells (S1), a decrease in the proportion of medium-sized cells (S4, S5) and the appearance of large cells (S6 to S9). These results seem to indicate close interrelationships between voluntary food intake, body weight and body compositon in sheep.