Developmental growth and body weight loss of cattle. I. Experimental design, body weight growth, and the effects of developmental growth and body weight loss on the dressed carcass and the offal

Abstract

At the age of approximately 11 months, 19 Angus steers were allotted to two experimental groups, namely, 10 to group A and 9 to group B. Group A animals were grown in pens and fed ad libitum. They were killed, two at each of the following of body weights: 250, 281, 316, 356, 400 kg. Group B animals were grown under similar conditions and killed at the same body weights as corresponding animals in group A; however, they were grown to weights 15% above their killing weights (growing-on phase) and then made to lose weight at 0.5 kg per day by restricting food intake until they reached their planned killing weights (weight loss phase). Huxley's (1932) allometric equation was used in logarithmic form as the basis for covariance analyses of the data. Empty body weight (EBW) increased as a proportion of full body weight as full body weight increased. EBW was higher in group A animals than in group B animals at the same full body weight, reflecting differences in weight of contents of the digestive tract. Dressed carcass weight increased as a proportion of EBW as EBW increased. Dressed carcass weight was higher in group B animals than in group A animals at the same EBW, indicating that the increase in carcass weight that occurred during the growing-on phase was not completely lost during the weight loss phase. During developmental growth, the weights of hide, feet, head, liver, gall bladder, heart, lungs, kidneys, and gut tissue decreased as proportions of EBW. The weight of abdominal fat increased as a proportion of EBW, while the weights of tail, spleen, and blood did not change significantly as proportions of EBW. During body weight loss, the weights of the feet, head, and tail remained close to the weights they had reached at the end of the growing-on phase, although, with the head, this varied considerably with the size of the animal before undergoing body weight loss. All other components lost weight during the weight loss phase. The hide, heart, lungs, and abdominal fat all reversed, approximately, the pattern of development that occurred during body weight growth. The liver, gall bladder, kidneys, gut tissue, spleen, blood, and thymus gland all lost more weight during the weight loss phase than they put on during the growing-on phase. With the liver, kidneys, and gut tissue, the proportion of weight lost varied according to the size of the animal before undergoing body weight loss.