Effect of somatotropin on rate and composition of gain and feed intake in young, pituitary intact female rats.

The effects of recombinant porcine somatotropin on rate and composition of gain in the carcass, and feed intake, and the consequences of somatotropin treatment withdrawal in young, growing, pituitary intact rats were investigated. Female Sprague-Dawley rats were assigned to one of two groups for a 21 day treatment phase, and a 14 day withdrawal phase: 1) Control, saline injected; 2) Somatotropin, 2 mg porcine somatotropin/d. During the 21 day treatment phase, somatotropin increased rate of body weight gain (46%), average daily feed intake (11%), and feed conversion efficiency (30%), relative to the control group. Upon withdrawal of somatotropin, there was a reversal of these effects relative to the treatment phase and to the controls. Somatotropin increased carcass protein accretion rate by 82% during the treatment phase. Upon cessation of treatment, protein accretion was decreased by 67% relative to the control group. The rates of carcass lipid accretion (g/d) were increased 44% over the control group during the treatment phase, but were decreased (49%) upon withdrawal. This data demonstrates that somatotropin is able to stimulate greater than normal growth in rapidly growing young female rats, but upon withdrawal of exogenous somatotropin, many of the benefits are not sustained.