This study aimed to describe the endocrine, cellular, and transcriptomic changes associated with mild heat stress responses in Wugu-Hu and Hu rams. Testicular samples from rams exposed to 3 days of scrotal insulation, resulting in an approximate 3 °C increase in scrotal temperature, and corresponding controls were analyzed for endocrine activity, seminiferous tubule morphology, germ cell composition, and transcriptomic profiles. There were no significant changes in testosterone, follicle-stimulating hormone, or luteinizing hormone after 3 days of mild heat exposure in either breed. Wugu-Hu rams showed greater disorganization of seminiferous tubules. Apoptotic events occurred mainly from spermatocytes to spermatids and were accompanied by a greater decline in spermatids in Wugu-Hu rams. Comparative transcriptomic analysis between Wugu-Hu and Hu rams identified 854 differentially expressed genes, mainly enriched in immune response function. We conclude that scrotal heat stress does not disrupt endocrine balance at the level applied in this study, but it induces breed-dependent morphological and testicular cellular responses. The differences in the immune response of Hu and Wugu-Hu rams may contribute to their distinct levels of spermatocytes and spermatids’ response to elevated temperatures.
chen et al. (2026) studied this question.