THE EFFECT OF LIVE WEIGHT-GAIN AND LIVE WEIGHT-LOSS ON BODY-COMPOSITION OF MERINO WETHERS - NONCARCASS ORGANS

The weight of the noncarcass external tissues, thoracic organs, and visceral organs was measured during live weight gain (LWG) and live weight loss (LWL) to evaluate the effect of different periods of normal and retarded growth on noncarcass organs. Thirty-five Merino wethers were allowed ad libitum access to an experimental diet of 80% alfalfa chaff and 20% cereal grain (17.23% CP and 12.09 MJ/kg of DE) to grow from 23.0 to 33.0 kg live weight and then fed to lose 10 kg at 133 g/d. Groups of five animals were slaughtered at live weights of 23.0, 26.3, 29.6, and 33.0 kg during LWG and 29.6, 26.3, and 23.0 kg during LWL. Although total weight of noncarcass organs was significantly lower in LWL animals than in LWG animals at 23.0- and 26.3-kg (P < .05) common slaughter weights, the weight of some noncarcass organs was significantly greater in LWL animals. For example, the weight of the head at 23.0 and 26.3 kg (P < .05), of the feet and esophagus at 23.0 (P < .01) and 26.3 kg (P < .05), and of the total alimentary tract fat at 23.0 kg (P < .01) was greater in LWL wethers. Weights of other organs, however, were lower in LWL animals. Weights of skin at 23.0 kg (P < .05), liver at 23.0 (P < .05), 26.3, and 29.6 kg (P <.01), kidneys and pancreas at 23.0 and 26.3 (P < .01), and 29.6 (P < .05), lymph glands at 23.0 (P < .01) and 29.6 kg (P < .05), and total alimentary tract tissue at all common slaughter weights (P < .01) were lower in LWL wethers. The lower total weight of noncarcass organs of LWL animals than of noncarcass organs of LWG animals at the same fleece-free empty BW was due to the mobilization of skin, liver, kidneys, pancreas, lymph glands, rumen-reticulum, and small and large intestines at higher rates during LWL than during LWG.