The effects of in ovo administration of testosterone or an antiandrogen ongrowth of chick embryos and embryonic muscle characteristics

Based on earlier studies from our laboratory, we hypothesized that higher l evels of plasma androgens in male embryos stimulate greater muscle developm ent and are responsible for the greater muscle mass of male chickens after hatching, The results of these studies show that androgen supplementation b y in ovo injection of testosterone prior to incubation had no effect on wei ght of 12-, 16-, or 20-d-old male chicken embryos or on characteristics of their Pectoralis superficialis muscle. In contrast, weight of 12 d-old fema le embryos was depressed and the protein concentration and protein content of the P. superficialis was reduced in 16-d-old female embryos. Interferenc e with the actions of endogenous androgens by preincubation in ovo injectio n of Flutamide (R), an antiandrogen, resulted in significant linear and qua dratic relationships between the dose of Flutamide injected and the weight, protein content, and DNA content of the P. superficialis of 16-d-old femal e embryos. Increases over the lower part of the dose range (0 to 1.74 mu mo l per egg) were followed by a decrease at the highest dose (2.9 mu mol per egg). The DNA content of the P. superficialis of 16-d-old female embryos wa s similarly affected when Flutamide was injected on Day 8 of incubation, wh ereas the protein content and protein concentration of the muscle was incre ased in 20-d-old female embryos. There were no significant changes in the w eight, protein content, or DNA content of the P. superficialis of male embr yos when Flutamide was injected before or on Day 8 of incubation.