CHANGES IN THE BODY-COMPOSITION OF BEEF-CATTLE DURING COMPENSATORY GROWTH

Forty-two weaned suckled Charolais-cross steers were used to measure changes in body composition during compensatory growth in growing cattle. Six cattle were slaughtered initially and the remaining 36 allocated to either a low level of feeding to 350 kg live weight followed by a high level (LH) or a high level of feeding throughout (HH). Above 350 kg live weight, food intake on both treatments was the same at any given live weight. Six cattle were slaughtered from each treatment at 350, 400 and 450 kg live weight. From initial live weight (259 kg) to 350 kg, live-weight gains were 0.45 and 0.78 kg/day for the LH and HH treatments respectively (P < 0.001). From 350 to 400 kg live weight, live-weight gains were 1.35 and 0.98 kg/day (P < 0.01) for the LH and HH cattle respectively, while from 400 to 450 kg live weight there was no significant difference (1.38 v. 1.20 kg/day). The LH cattle contained less fat in the empty body than the HH cattle at 350 kg (118 v. 153 g/kg; P < 0.05) and 400 kg live weight (117 v. 169 g/kg; P < 0.01), but at 450 kg there was no significant difference between treatments. From 350 to 400 kg live weight the composition of the empty body-weight gain was 663 g water, 108 g fat and 216 g protein per kg in the LH cattle and 422 kg water, 311 g fat and 173 g protein in the HH cattle. From 400 to 450 kg live weight the equivalent figures were 491, 291, 156 g/kg for the LH cattle and 744, 67 and 203 g/kg for the HH cattle. The results demonstrate that following a period of food restriction the empty body-weight gain of cattle initially comprises increased proportions of protein and water and a reduced proportion of fat compared with unrestricted cattle when both are given the same amount of food and compared at the same weight. There then follows a second phase in which the proportion of fat increases and the proportions of protein and water decrease.