The effect of letrozole administration on the aggressive behavior and reproductive parameters of male goats (Capra hircus)

Estrogens have been showed to be important for reproduction in several species. These hormones are synthesized by the activity of P450- aromatase, an enzyme present in the testis. However information about their role in the male buck is scarce. The aim of this study was to investigate whether estradiol deprivation by treatment with the P450-aromatase inhibitor letrozole affects serum sex steroids, agressive behavior, or disrupts spermatogenesis in the male goat buck.Twelve bucks (Saanen) were included in the study, the herd was divided in two groups, 6 control, and 6 that received letrozole treatment that was administered by the route per os (PO) (2.5 mg/day) for 15 days. Blood samples were obtained from the jugular vein each third day during treatment, two samples along 4 days before beginning of the letrozole treatment, and two samples more along 4 days after the end of it. Serum 17β-estradiol and testosterone were measured by an enzymatic analysis (EIA). Simultaneously, the agonistic behavior of the goats was recorded daily for 3 h, evaluating butts, threats, chases and avoidance in order to create dominance matrices and investigate dominance levels in the groups. Testis circumference was measured and semen was collected by artificial vagina every 4 days. Semen characteristics were evaluated: Volume, color, mass and individual movement, concentration, viability, measured by eosine-nigrosin technique, and acrosome integrity by Coomasie. The results of this study showed that the goat aggressive behavior was increased by letrozole treatment, an effect probably associated to the rise in serum testosterone. The ejaculate volume and spermatic concentrations were significantly decreased after letrozole administration. Spermatozoa massive and individual movements began to decrease after the 5th sampling. In addition, dead spermatozoa significantly increased in the letrozole group and cells with an intact acrosome diminished in the letrozole group. In summary, the results of our study showed that inhibition of P450-aromatase by letrozol affects the male goat behaviour, semen production and spermatozoid characteristics, probably by blocking testis and reproductive tract intracrine and paracrine 17β-estradiol actions.