Phytoestrogens are non-steroidal compounds that, can act as agonists and/or antagonists by binding to estrogen receptors
consequently they can modify estrogen-dependent processes of neonatal sexual differentiation. Results of the analysis of the sexual behavior of experimental rats that received 6.8 mg of isoflavones/kg/day, showed significantly more mating activity, but fewer ejaculations (p <
0.01), and a lower copulatory efficiency than the control group. Aggressive behavior was prominent in the phytoestrogen-treated males (p <
0.05), but defensive behavior was infrequent. Phytoestrogens may interfere with the development of male and female traits by competing with estradiol in contexts of sexual behavior. Compared to the control group, the phytoestrogen-treated males exhibited delayed olfactory perception and uncertain preference. The ventrolateral area of the medial hypothalamus is influenced by neonatal neuro estrogens that can produce changes in differentiation, such as the aggressiveness manifested by the males. A probable explanation is that this is due to the inhibition of aromatase by isoflavones. Regarding fertility, the females impregnated by the control males had more offspring (12.2 ± 2.10), than those of the experimental males (4.02 ± 1.13, p <
0.01). Spermatozoa analysis showed a low concentration (p <
0.05) due to isoflavone treatment, with increased immaturity (p <
0.01) and more dead spermatozoa (p <
0.05). We conclude that neonatal administration of genistein and daidzein alters olfactory functions, aggressiveness, sexual behaviors, and fertility through changes in spermatozoa quality. The most notable effect was the decreased of fertility in experimental male demonstrated by the lower number of pregnant females and smaller litters.