Testis size, peripheral concentrations of testosterone, semen criteria and Sertoli and germ cell numbers in Nelore bulls

Abstract

A study was conducted to evaluate the associations among testis size, testosterone concentrations, semen parameters and aspects of spermatogenesis in Nelore bulls (n = 28). Testis size was measured from 10 to 29 months of age. Bulls were treated with GnRH (12 to 21 months) and semen samples also collected from 25 to 29 months. At 30 months, animals were slaughtered. Correlations were significant when p < 0.05. Basal testosterone was highest at 18 months, suggesting that bulls reached puberty at this age. At 30 months, seminiferous tubules represented 77.9 ± 3.8 % of the testicular parenchyma and there were 33.6 ± 8.4 round spermatids/A1 spermatogonium/tubule section, indicating a 47.5% degeneration rate during spermatogenesis. At 30 months, heavier testis correlated with Sertoli cell numbers/testis (r = 0.77), and round spermatids/tubule section, Sertoli cell and A1 spermatogonium (r = 0.50 -0.60). Scrotal circumference (SC) taken between 10 and 29 months correlated with the percentage of tubules with spermatids (r = 0.42 -0.59) and number of A1 spermatogonium and round spermatids/Sertoli cell (r = 0.49 -0.68). Epididymal weight was related to Sertoli cell numbers/testis, and round spermatids/ Sertoli cell and A1 spermatogonium (r = 0.51 -0.61). GnRH-stimulated testosterone from 17 to 21 months correlated with SC between 14 and 29 months (r = 0.48 -0.60), testis and epididymal weights (r = 0.41 -0.64) and with parameters of spermatogenesis (r = 0.44 -0.58). Additionally, sperm motility and vigor from 25 to 29 months correlated with the number of tubules with spermatids (r = 0.42 -0.59) and GnRH-stimulated testosterone at 12, 13 and 18 months (r = 0.46 -0.57). In conclusion, testis size during and after the period of pronounced increases in testosterone is an indicator of quantitative parameters of spermatogenesis of post-pubertal bulls. Key words: Nelore, sperm motility, spermatogenesis, testis, testosterone ResumoConduziu-se o presente estudo com o objetivo de avaliar as associações entre biometria testicular, testosterona, parâmetros seminais e aspectos da espermatogênese em touros Nelore (n = 28). Avaliou- se os testículos dos 10 aos 29 meses de idade. Os touros foram tratados com GnRH (12 a 21 meses) e amostras de sêmen coletadas (25 a 29 meses). Aos 30 meses, os animais foram abatidos. Correlações foram consideradas significativas quando p < 0.05. Concentrações elevadas de testosterona basal ocorreram aos 18 meses, indicativo da puberdade dos touros. Aos 30 meses, os túbulos seminíferos representaram 77,9 ± 3,8% do parênquima testicular e quantificou-se 33,6 ± 8,4 espermátides arredondadas/espermatogônia A1/secção tubular, referente a 47,5% de degeneração celular durante a espermatogênese. Aos 30 meses, peso testicular correlacionou-se com o número de células de Sertoli/ testículo (r = 0,77) e espermátides arredondadas/seção tubular, célula de Sertoli e espermatogônia A1 (r = 0,50 -0,60). A circunferência escrotal (CE) entre 10 e 29 meses correlacionou-se com a percentagem de túbulos com espermátide...