Heat stress impact on reproductive and physiological performance of Barbados Blackbelly rams under different management systems in the tropics

Tropical regions face climate change, which increases the impacts of heat stress (HS) on ram fertility. Twenty-four Barbados Blackbelly rams were divided into intensive (ITS) and semi-intensive (SIS) management systems. ITS rams were housed in a barn, while SIS rams spent six hours daily outside over two months. Daily climate data were collected, and the Temperature-Humidity Index (THI) was calculated. Weekly semen collections and physiological assessments were conducted. Sperm motility was evaluated using a Computerised Assisted Sperm Analyser (CASA), alongside sperm viability, morphology, hormone levels, and oxidative stress. SIS rams experienced more severe heat stress, indicated by higher physiological responses ( p  < 0.05) than ITS rams. SIS sperm quality was significantly lower, with reduced motility, progressive motility, kinematic parameters, morphology, and viability ( p  < 0.05). Testosterone and cortisol levels showed no significant differences between systems, though ITS had higher testosterone and SIS had elevated cortisol. MDA ( p  < 0.001) and H ₂ O ₂ ( p  < 0.05) followed similar trends, with SIS rams showing higher oxidative stress levels. The THI for SIS was significantly greater than that of ITS, potentially affecting adaptable breeds like Barbados Blackbelly, resulting in lower fertility in SIS rams. Despite exceeding the THI threshold, the minimal impact on physiological responses in ITS rams suggests a contradiction, indicating a need for a specific classification of heat stress severity, with a focus on humidity in the tropics. Although heat stress (HS) impacts reproductive performance, physiological functions, and oxidative stress parameters, it does not significantly lead to infertility, and the rams generally remain fertile.