Effects of Summer Heat Stress on Physiological Parameters and Reproductive Efficiency of Barbarine Ewes Under Natural Outdoor or Indoor Conditions

Climate change and rising ambient temperatures increasingly challenge sheep production systems in arid and semi-arid regions, particularly during the summer breeding season. This study evaluated the effects of heat stress and direct solar exposure on physiological responses, metabolic profile, and reproductive performance of Barbarine ewes, a fat-tailed breed adapted to harsh environments. A total of 112 non-lactating multiparous ewes were allocated to two groups during summer mating: an indoor group protected from solar radiation (IDGp; n = 58) and an outdoor group exposed to direct sunlight (ODGp; n = 54). Both groups experienced severe to extreme heat stress for more than 65% of the experimental period. Sun exposure significantly increased rectal temperature (+0.2 to +0.6°C), respiratory rate (up to 130 vs 61 breaths/min), and heart rate (up to 95 vs 87 beats/min) in outdoor ewes (ODGp) compared to indoor ewes (IDGp), indicating a higher physiological heat load in sun-exposed animals. The temperature-humidity index (THI) remained comparable between groups (≈24.7), suggesting comparable THI values. Metabolic responses were characterized by increased plasma concentrations of triglycerides (+36%), total proteins (+7.5%), urea (+13%), creatinine (+34%), and potassium (+5%), along with a decrease in cholesterol levels (-15%) in ODGp compared to IDGp. Despite these physiological and metabolic adjustments, body condition score and live weight were maintained in both groups. Reproductive performance was not affected by solar exposure, with estrus occurrence exceeding 94%, an ovulation rate of 1.17, and no significant differences in fertility (79.3% vs 77.8%), prolificacy, or fecundity between groups. These findings indicate that, although direct solar radiation increases physiological strain, it does not impair reproductive function under comparable ambient thermal conditions. Barbarine ewes thus exhibit strong functional resilience to heat stress, highlighting their suitability for extensive production systems in hot and dry environments.