Rooster fertility peaks between 30 and 40 weeks of age and declines rapidly from 50 weeks of age. This is linked to a reduction in the number of spermatozoa in the ejaculate due to high density of spermatids in the seminiferous tubules of low-fertility roosters. In this study, we assessed the effects over spermatogenesis of both letrozole, an aromatase inhibitor, and a commercial herbal extract designed for improving fertility composed by Tribulus, Cinnamomum, Zingiber and Sativus. Forty-two- week- old Ross 308 roosters (n = 24) were distributed into four groups: control, letrozole (0.03 mg/kg), herbal extract (0.04 ml/kg) and letrozole+herbal extract. After 14 weeks of daily oral supplementation, their testes and epididymides were weighed, fixed and sectioned for assessment of spermatogenesis and quantification of sperm cells inside the lumen. Differences in seminiferous tubules measurements and density of sperm cells were tested using R software (version 3.0.1). Although body weight was not affected by the treatment, testes from animals treated with the combination of letrozole and herbal extracts were heavier than those from control animals. Animals treated with either letrozole or herbal extract, or their combination, showed a significant higher number of sperm cells inside the seminiferous tubules and epididymis than control animals (p < .05). These data suggest that the use of letrozole and the herbal extract could improve sperm cell production in ageing roosters. Future studies are needed to disclose the causal mechanisms involved and its effect on fertility and ejaculate features.
