A novel paradigm in the prediction of the performance of breeding buffalo bulls: role of hair cortisol and testosterone.

Despite having strong pedigree records, passing breeding soundness evaluations, and receiving appropriate management and nutrition, some breeding bulls consistently underperform in similar environmental conditions where other bulls thrive. These underperforming bulls are economically unsuitable for semen stations that produce semen doses. Our study aims to predict the performance of breeding bulls based on hair cortisol and testosterone concentrations. We also measured these hormones in buffalo calves. Furthermore, we assessed seminal plasma cortisol and testosterone concentrations in poor-quality and good-quality ejaculates. To evaluate bull performance, we categorized the bulls into two groups based on ejaculate discard rates: consistent (n = 9) and inconsistent semen quality bulls (n = 6). The breeding bulls' hair cortisol and testosterone levels were evaluated at two-month intervals for one year. We analyzed the semen from both groups for motility and kinematic parameters using a computer-assisted semen analyzer and acrosome integrity, mitochondrial membrane potential, and superoxide production through flow cytometry. The bulls that exhibited consistent semen quality had higher (P < 0.05) hair testosterone concentrations than those with inconsistent quality; however, there was no difference (P > 0.05) in hair cortisol levels between the two groups. Additionally, the ejaculates from bulls with inconsistent semen quality met minimum standards, showing no differences (P > 0.05) in sperm motility. However, mitochondrial membrane potential and superoxide production were compromised at the subcellular level. Acrosome integrity was also lower (P < 0.05) in bulls with inconsistent semen quality than those with consistent quality. In poor-quality ejaculates, regardless of the bull group, cortisol and testosterone concentrations were higher (P < 0.05) than in good-quality ejaculates intended for cryopreservation. Additionally, hair testosterone concentration increased with age in male calves, while hair cortisol levels were higher during July-August and lower from March to April. In conclusion, bulls that exhibited consistent semen quality appear stress-tolerant, while those with inconsistent quality are more stress-susceptible. Our findings suggest that hair testosterone is a better indicator of stress in breeding bulls than hair cortisol.