Interaction of thyroxine and testosterone in stimulating muscle protein breakdown in female broiler chickens

The effects of thyroxine (T4), testosterone propionate (TP) and a combination of hormone treatments on growth and the rates of muscle protein breakdown estimated by Ntau-methylhistidine excretion were studied. 2. Broiler chickens aged from 15 d to 27 d were used; T4 and TP were mixed in the basal diet at concentrations of 1.2 and 20 mg/kg respectively. 3. Although growth was not altered significantly by any treatment, the rate of muscle protein breakdown was significantly increased about 2-fold by the combined treatment, but not by treatment with T4 or TP alone.