Scrotal thermography for evaluating temperature gradients and their association with semen quality and stress biomarkers of Karan Fries (Holstein Friesian × Tharparkar) and Tharparkar bulls under tropical climatic conditions

Present study evaluated the influence of different seasons and testicular temperature gradient (TTG) on semen quality, physiological responses and oxidative stress biomarkers of Tharparkar and Karan Fries (KF) bulls (five each) maintained under standard conditions of feeding and management at ABRC, ICAR-NDRI, Karnal (Haryana), India. TTG was determined using infrared thermography (Therma Camera SC2000, FLIR Systems, Inc. Wilsonville, OR, USA) of the scrotal surface (proximal, mid-pole, distal). The rectal temperature, respiration rate, semen quality traits and blood biomarkers (MDA, HSP70, ROS, and testosterone) were also assessed across seasons in both the breeds. TTG was significantly lower (p < 0.05) in KF and during summer compared to Tharparkar and other seasons, respectively, coinciding with higher physiological strain, elevated oxidative stress markers, and reduced semen quality. In contrast, Tharparkar bulls maintained better semen quality and lower sperm abnormalities, with higher testosterone levels across seasons. Temperature – humidity index (THI) was negatively correlated with TTG and semen quality parameters in both the breeds of bull. These findings underscore the superior resilience of Tharparkar bulls during heat stress compared to KF bulls and highlight the importance of breed-specific reproductive management strategies under tropical climatic conditions for better semen quality and welfare.