Influence of temperature–humidity index and seasonal variations on semen quality, scrotal circumference, and hormones in Kail rams raised under subtropical climate

Context Seasonality plays a vital part in determining the profitability of ovine farms, particularly in tropical and subtropical regions, where environmental factors influence reproductive efficiency. Understanding seasonal variations in semen quality, testicular parameters, and hormonal profiles is essential for optimizing breeding strategies in Kail rams. Aims The purpose of this study was to evaluate monthly variations in semen quality, scrotal circumference (SC), testicular echogenicity (TE), and plasma testosterone and melatonin concentrations in adult Kail rams. Methods Five adult Kail rams (2–3 years old) were monitored over 1 year. Semen was collected thrice monthly, testicular ultrasonography was performed, and blood samples were taken monthly. Semen parameters, SC, TE, and hormone concentrations were analyzed in relation to environmental variations, including temperature–humidity index (THI). Key results Semen volume (0.7 ± 0.03 mL) and SC (25.1 ± 0.6 cm) were lowest in January, peaking in September and July respectively. In December, sperm motility and kinematics were at their lowest. TE values were lowest in September and highest in January. No significant monthly variations were observed in testosterone and melatonin concentrations. Semen volume (R2 = 0.70), sperm total motility (R2 = 0.62), progressive motility (R2 = 0.65), rapid sperm (R2 = 0.68), curvilinear velocity (R2 = 0.83) and TE (R2 = 0.47) correlated significantly with THI. TE negatively correlated with sperm motility, kinematics, SC, and plasma testosterone and melatonin concentrations, whereas SC showed a positive correlation with sperm-quality parameters. No significant association was found between SC and hormonal concentrations. Conclusions Seasonal variations significantly influenced sperm motility, kinematics, SC, and TE, whereas testosterone and melatonin concentrations remained unaffected. The optimal THI range for semen production was 58–72. Implications These findings have highlighted the importance of seasonal reproductive management in tropical and subtropical ovine farming systems. TE could serve as a useful predictor of sperm quality, whereas SC may be a positive indicator of reproductive performance in Kail rams.