The influence of tropical adaptation and breedtype on adrenal and testicular function in beef bulls

Bulls of various breedtypes including Angus (Bos taurus), Bonsmara (Sanga X Bos taurus), Brahman (Bos indicus), Romosinuano (Criollo), Tuli (Sanga) and Wagyu (Japanese Bos taurus) were utilized to evaluate the influence of tropical adaptation on adrenal and testicular function. The objectives were to determine if tropical adaptation influenced: a) response to management stressors, b) organ and gland weights, adrenal and testis StAR and P450 content and total adrenal, medullary and cortical areas, c) basal and hCG-induced testosterone and d) testis and epididymal sperm concentrations. Blood samples were obtained within 5 min before and after transportation and during restraint every 15 min for 6 h to evaluate cortical response. Angus, Brahman and Romosinuano bulls were slaughtered following sexual maturity. Cortical responses to transportation and restraint were not influenced by tropical adaptation. Response to these stressors could be categorized into high responders (Angus, Brahman), intermediate responders (Romosinuano, Tuli) and low responders (Wagyu, Bonsmara). Tropically-adapted breedtypes were not categorized into a single group; therefore, cortical responses to management stressors were influenced by breedtype, but not by tropical adaptation. Most organ and gland weights (actual weight and weight corrected for BW) and the steroid precursors, StAR and P450, were not influenced by tropical adaptation, but were by breedtype. Paired adrenal gland weight, total adrenal area, medullary and cortical areas were influenced by tropical adaptation. Tropically-adapted breedtypes had lighter glands and smaller areas than the temperate Bos taurus breedtypes. All breedtypes except Wagyu had similar basal concentrations of plasma testosterone prior to hCG administration; therefore, basal testosterone was not influenced by tropical adaptation, but only by breedtype. Wagyu had greater basal concentrations of testosterone than other breedtypes. Testosterone concentrations following hCG administration was similar between adaptation groups and breedtypes. As expected, testis and epididymal sperm concentrations were influenced by tropical adaptation. Tropically-adapted breedtypes had greater testicular and epididymal sperm concentrations than the temperate Bos taurus breedtypes during the summer months. In summary, adrenal weight and area and testicular and epididymal sperm concentrations were influenced by tropical adaptation. Cortical response to management stressors, basal testosterone and StAR and P450 content were influenced by breedtype, not tropical adaptation.