Degree of sex differentiation of genetic female chicken treated with different doses of an aromatase inhibitor.

Injection of an aromatase inhibitor before gonadal sex differentiation can induce female-to-male sex reversal in chicken, but a higher dose could reduce hatchability. In the present study, the dosage effect of Fadrozole, a nonsteroidal aromatase inhibitor, on gonadal differentiation was analyzed in sex-reversed genetic female chicken. There was no significant difference for the hatchability among low-dose (0.1, 0.3 and 0.5 mg) Fadrozole-injected groups and control groups (p > 0.05), but in high-dose groups (1.0 mg and 1.3 mg) the hatchability was significantly reduced (p < 0.05). Complete phenotypic sex reversal was observed in both high- and low- dose groups, with more than 90% of genetic females reversed into phenotypic male chicks. The degree of gonadal differentiation in 124 chicken at 30 weeks of age was classified into 5 categories according to the visual appearance and histological structure of the gonads. Category I and V were standard ovary and testis, respectively, while category II, III, and IV represented gonads of slightly, moderately, and highly sex-reversed females, respectively. Most gonads in low-dose groups were classified into category I, II, and III, while those in high-dose groups were mainly category IV. The serum testosterone levels in the 1.3 mg group were significantly higher and the estradiol levels lower than those in low-dose groups (p < 0.05). In conclusion, the range from 0.5 to 1.0 mg Fadrozole is a key interval for survival of chicken embryos. The gonadal differentiation in sex-reversed females at 30 weeks of age is highly dependent on the dose of Fadrozole injected prior to gonadal sex differentiation.