Maternal heat stress in Bos indicus and Bos taurus Cattle: evolutionary adaptation and reproductive responses

Heat stress adversely affects the productivity of the herd, especially the reproductive performance of cattle, posing a persistent challenge for cattle farming. This issue is particularly evident in Bos taurus (taurine) breeds of European origin, whose genetic selection was primarily focus on production traits rather than heat tolerance. In contrast, Bos indicus (zebu) breeds are more resilient to high temperatures and humidity due to evolutionary history that led to physiological, cellular and molecular adaptations to hot environments. This adaptation has a significant consequence not only on the capacity to regulate body temperature when compared with B. taurus, represented by the ability to cope with higher temperature-humidity index, but also how follicle cells, oocytes and embryos deal with high temperatures. Indeed, zebu oocytes and embryos display better development performance when exposed to heat stress than taurine ones. This may be due to differential gene expression and epigenetic modifications that can play a role in protecting them from the deleterious effect of heat stress, favoring the preimplantation development. Specific alleles may further enhance the resilience observed in zebu cattle. However, these conditions appear insufficient to confer tolerance to prolonged and severe heat stress in zebu oocytes. Although paternal factors may contribute to early embryo development, the zebu embryo resilience to heat stress seems to rely on maternal contribution. Examining the genomic diversity between B. indicus and B. taurus may enable the identification of genomic and epigenomic markers that elucidate the observed differences between these subspecies.