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 compositio n of gain in the carcass, and feed intake, and the consequences of som atotropin treatment withdrawal in young, growing, pituitary intact rat s were investigated. Female Sprague-Dawley rats were assigned to one o f two groups for a 21 day treatment phase, and a 14 day withdrawal pha se: 1) Control, saline injected; 2) Somatotropin, 2 mg porcine somatot ropin/d. During the 21 day treatment phase, somatotropin increased rat e of body weight gain (46%), average daily feed intake (11%), and feed conversion efficiency (30%), relative to the control group. Upon with drawal of somatotropin, there was a reversal of these effects relative to the treatment phase and to the controls. Somatotropin increased ca rcass protein accretion rate by 82% during the treatment phase. Upon c essation 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 soma totropin is able to stimulate greater than normal growth in rapidly gr owing young female rats, but upon withdrawal of exogenous somatotropin , many of the benefits are not sustained.