Developmental growth and body weight loss of cattle. V. Changes in the alimentary tract

Abstract

This paper describes an investigation of the effects of developmental growth and body weight loss on the alimentary tract of Angus steers. Two groups of steers were used: group A which grew continuously, and group B which grew like group A and were then subjected to a period of weight loss before slaughter. Corresponding animals in both groups were killed at the same body weights. Group A animals (and group B animals before the commencement of weight loss) were fed on a high quality ration ad libitum. During their period of weight loss the group B animals were given a restricted intake of oaten straw. Statistical analysis was by analysis of covariance of the weights of components converted to logarithms. As empty body weight (EBW) increased, the weight of the empty, fat-trimmed alimentary tract (GT), the weight of each component of GT (oesophagus, rumenreticulum, omasum, abomasum, small intestine, caecum, colon-rectum), and the weight of contents in each component of GT decreased as proportions of EBW. Apart from the oesophagus and the caecum, GT and each of its components did not change significantly in weight as the live body weight of the animals increased from 250 to 400 kg. Thus, developmental growth of the alimentary tract had almost finished when the experiment began. The effect of weight loss on the components of the alimentary tract was independent of EBW except for weight of the rumen-reticulum. This component lost weight in all animals but the loss was relatively smaller in the heavier animals than in the lighter ones. When group A and group B animals were compared at the same EBW, the weight of GT in group B animals was significantly less than in the group A animals. However, the components of GT did not all behave in the same way. Thus the weight of the oesophagus was greater, weights of the abomasum and small intestine were less, and weights of the omasum, caecum, and colon-rectum were not significantly changed in group B animals when compared with group A. Also, there was more digesta and its dry matter percentage was less in group B than in group A. The overall loss of weight of GT during body weight loss was an indication that GT was used as a source of protein and energy. The changes in the weights and relative proportions of the components of GT during weight loss were thought to be a reflection of the change both to a poor quality ration and to a reduced food intake.