Testicular, semen and blood parameters in adapted and nonadapted [formula omitted][formula omitted] bulls in the semi-arid tropics

Abstract

Two experiments were conducted to evaluate differences in testicular, seminal and hematological characteristics in adapted (Senepol) and nonadapted (Holstein) Bos taurus bulls under the semi-arid environmental conditions of St. Croix, Virgin Islands (17°N, 64°W). In Experiment 1 mature, sexually-rested Senepol (n=10) and Holstein (n=9) bulls of similar age (37 months) and body weight (715 kg) and grazing on adjacent native pastures, were tested on the same day in July (28.8°C mean ambient temperature, 81.5% humidity). Senepol bulls had lower (P<0.01) rectal temperatures (39.3 vs 40.0°C) and higher (P<0.01) packed cell volumes (41.4 vs 35.2%) than Holstein bulls. Scrotal circumference was 3 cm larger (P<0.1) and testis tone firmer (P<0.001) in Senepol compared to Holstein bulls. Ejaculates, obtained by electroejaculation, contained 3.2×10 9 more spermatozoa with fewer abnormal tails and detached acrosomes in Senepol than in Holstein bulls (P<0.05). In Experiment 2, Senepol (n=42) and Holstein (n=30) bulls, representing 3 beef and 5 dairy farms, were evaluated during the summer (August/September) and winter (February/March). Again, scrotal circumference was larger (P<0.05) and testis tone firmer (P<0.001) in Senepol than in Holstein bulls, with no effect of season. Seminal fructose was higher (P<0.01) in Senepol than in Holstein bulls and decreased (P<0.01) during the winter collection. Blood plasma urea nitrogen and glucose were similar between breeds, but urea nitrogen was lower (P<0.01) during the summer. Significant (P<0.01) breed-by-age interactions were observed for the frequency of spermatozoa with protoplasmic droplets, decreasing in Holstein but not in Senepol bulls. The data point to differences between the adapted and nonadapted breed type in testicular and ejaculate characteristics, but also suggest that season has only a limited impact on bull reproductive function under the environmental conditions in St. Croix.