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

Based on earlier studies from our laboratory, we hypothesized that higher levels of plasma androgens in male embryos stimulate greater muscle development and are responsible for the greater muscle mass of male chickens after hatching. The results of these studies show that androgen supplementation by in ovo injection of testosterone prior to incubation had no effect on weight 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 female embryos was depressed and the protein concentration and protein content of the P. superficialis was reduced in 16-d-old female embryos. Interference with the actions of endogenous androgens by preincubation in ovo injection of Flutamide, an antiandrogen, resulted in significant linear and quadratic relationships between the dose of Flutamide injected and the weight, protein content, and DNA content of the P. superficialis of 16-d-old female embryos. Increases over the lower part of the dose range (0 to 1.74 micromol per egg) were followed by a decrease at the highest dose (2.9 micromol per egg). The DNA content of the P. superficialis of 16-d-old female embryos was similarly affected when Flutamide was injected on Day 8 of incubation, whereas the protein content and protein concentration of the muscle was increased in 20-d-old female embryos. There were no significant changes in the weight, protein content, or DNA content of the P. superficialis of male embryos when Flutamide was injected before or on Day 8 of incubation.