Climatic impact on ram lamb reproductive development: the effect of solar radiation

Climate change has a significant impact on global animal production. The objective was to evaluate the long-term effects of direct solar radiation on reproductive development in Pelibuey ram lambs under heat stress. Eighteen ram lambs (6.9 ± 1.1 months of age; 25.7 ± 7.9 kg body weight) were allocated to either shaded pens under a galvanized roof ( ROR ) or unshaded pens ( EXPR ) for ten months in a warm subhumid environment (air temperature = 37.3 °C; temperature–humidity index = 85.1 units). Monthly assessments included scrotal circumference, scrotal surface temperature, semen collection (volume, concentration, mass motility, and kinetic parameters), serum testosterone concentration, and standardized sexual behavior tests. The semen was collected using an electroejaculator. At the end of the trial, testicular cytology was performed via fine needle aspiration. EXPR lambs exhibited greater scrotal circumference (29.6 vs 25.7 cm; P = 0.003) and lower scrotal temperature (35.9 vs 36.6 °C; P = 0.0006). Semen from EXPR lambs had higher sperm concentration and mass motility (P < 0.01) and increased curvilinear, average path, and straight-line velocities (P < 0.01). EXPR lambs also displayed more anogenital sniffing, mounts, and ejaculations (P < 0.05). Cytology revealed a higher proportion of late spermatids in EXPR lambs, while serum testosterone was slightly higher in ROR lambs (P < 0.05). The interaction between treatment and time across most evaluated variables indicates that the effects of solar radiation exposure are not static but fluctuate over the experimental period, likely influenced by seasonal variations in solar radiation intensity, air temperature, and day length. The ability of EXPR animals to maintain superior performance in certain months (e.g., higher sperm concentration in November, January, March, and June, or higher mass motility from December to April) reaffirms the idea of a resilient or adaptive capacity, enabling them to thrive at different times of the year—even when environmental conditions might be more challenging.