Effects of diet, bacitracin, and body weight restrictions on the intestine of broiler chicks.

Six experiments were conducted to evaluate the effects of diet, bacitracin, and body weight restrictions on the intestine of the broiler chick. Bacitracin, at levels of 11 and 55 ppm, significantly increased body weight, significantly reduced small intestine weight, but had no significant effect on liver weight of chicks fed a soybean protein and sucrose-based diet. The greatest effects were observed in the ileum where weight, moisture, length per unit of body weight, and dry matter per unit of length were all significantly reduced. The least effects were observed in the duodenum where weight and length per unit of body weight were significantly reduced and dry matter per unit of length was significantly increased. Intestinal weight, as a percent of body weight, was not significantly affected when body weight was suppressed with a high level of nicarbazin added to a practical diet, but it was significantly reduced when bacitracin was added to the semipurified diet and chicks were restricted in food intake to 70% of controls. A level of 55 ppm of bacitracin added to the practical diet had no significant effect on body weight, intestinal weight, or liver weight. As discussed, the observed changes in the intestine, due to bacitracin, are probably indirect and most likely reflect the action of the antibiotic on the intestinal microflora.