Effects of dietary soybean isoflavones (SI) on reproduction in the young breeder rooster

Soybean isoflavones (SIs) are phytoestrogens that competitive with estrogens in body. Although SIs play an important role in reproduction, their role in testicular development in roosters is unknown. This study was conducted to investigate the effect of SIs on testicular development and serum reproductive hormone profiles in young breeder roosters (70–133 days old). Gene expression of steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (P450scc), and 3β-hydroxysteroid dehydrogenase (3β-HSD), which are related to testosterone synthesis, in rooster testis were also evaluated after treatment with different SI doses. Although SIs had no significant effect on body weight, 5 mg/kg SIs significantly increased the testis index and serum levels of reproductive hormones (gonadotropin releasing hormone, follicle- stimulating hormone, luteinizing hormone, and testosterone).To further investigate whether SIs regulate hormone synthesis via StAR, p450scc, 3β-HSD, real time-PCR was performed to measure the mRNA levels of the corresponding genes. The results showed that 5 mg/kg of SIs significantly increased StAR mRNA levels. However, there were no significant effects on p450scc or 3β-HSD mRNA levels. Moreover, the spermatogonial development and the number of germ cell layers were increased by treatment with 5 mg/kg of SIs. These results suggest that SIs promote testicular growth by increasing reproductive hormone secretion, which is closely related to StAR expression, to positively regulate reproduction in young roosters.