Somatotropin treatment reduces energy intake without altering protein intake in pigs selecting between high and low protein diets.

The current experiment examined the effect of somatotropin (STH) on feed intake and diet selection in pigs selecting between high (24% CP) and low (12% CP) protein diets. Sixteen pigs (initial weight 69 +/- 2 kg) were individually penned and allowed to select between the diets for a 7-d pretreatment period and a 14-d treatment period during which time they received daily, subcutaneous injections of porcine somatotropin (0 or 4 mg/d). A 6-d withdrawal period followed. Feed intake was recorded daily. Over the 14-d treatment period, feed intake in pigs treated with STH was 21% less than that in the control group (2.49 vs. 3.17 kg/d, P < 0.01). The decrease in total intake was accounted for entirely by a decrease in the amount of the 12% CP diet selected (1.00 vs. 2.00 kg/d, P <0.01). STH-treated pigs altered their selection pattern such that energy intake was reduced, but total protein intake was unaffected. Control pigs selected a diet that was 15-16% crude protein throughout the study. STH-treated pigs selected a higher protein diet (18%, P < 0.02). During the withdrawal period, total feed intake began to normalize, such that by the third day of withdrawal, intake was not different than that in the control group. The recovery of total intake was accomplished by increased consumption of both diets rather than a specific normalization of low protein diet consumption. The results indicate that pigs treated with STH decrease feed intake, which is due to a decrease in the amount of 12% CP diet consumed. The change in dietary selection pattern is likely associated with a change in energy retention (carcass lipid + protein) associated with the STH-induced changes in composition of gain.