The effect of live weight gain and live weight loss on body composition of Merino wethers: chemical composition of the noncarcass organs and the empty body.

Chemical composition of the noncarcass organs, combined noncarcass organs, and fleece-free empty body (FFEB) was measured during live weight gain (LWG) and live weight loss (LWL) to determine the effect of different periods of normal and retarded growth on chemical composition of noncarcass organs and FFEB. Thirty-five Merino wethers had ad libitum access to the experimental diet (17.23% CP and 12.09 MJ/kg of DE) to grow from 23.0 to 33.0 kg live weight and then were fed to lose a total of 10 kg in three periods of 25 d each at the rate of 133 g/d. Groups of five wethers were slaughtered at live weights of 23.0, 26.3, 29.6, and 33.0 kg during LWG and 29.6 (first period), 26.3 (second period), and 23.0 kg (third period) during LWL. The lower combined noncarcass weight in LWL wethers than in LWG wethers at 23.0 and 26.3 kg of live weights was due to the significantly lower protein weight at 23.0 and 26.3 kg (P < .01) and water weight at all common slaughter weights (P < .01). Chemical fat in the combined noncarcass organs was significantly greater in LWL wethers than in LWG wethers at 23.0, 26.3 (P < .01), and 29.6 kg (P < .05). The general increase of chemical fat in the combined noncarcass organs of the LWL wethers was mainly due to the significant increase in the chemical fat in the head and feet at 23.0 (P < .01), 26.3, and 29.6 kg (P < .05), liver at 23.0 kg (P < .01), and total alimentary tract fat at 23.0 (P < .01) and 29.6 kg (P < .05). Although fleece-free empty body weight (FFEBW) was similar in LWG and LWL wethers at all common slaughter weights, FFEB water weight was lower significantly in LWL wethers at 23.0, 26.3 (P < .01), and 29.6 kg (P < .05) and that of chemical fat was greater significantly in LWL wethers at 23.0 (P < .01), 26.3, and 29.6 kg (P < .05) than in LWG wethers. Wethers after weight loss had more chemical fat and less water in their FFEB than normal growing wethers at the same FFEBW.