Vol. 8, Special Issue 9, Part K (2024)

Cattle reproduction is significantly hampered in the tropics and subtropics by a variety of causes and fertility of cattle depends on the ovulation of competent oocyte from the healthy follicular population and heat stress affects the follicular developmental pattern directly or indirectly, subsequently affect the fertility of the animal. Summer is one of the seasons that negatively affects cow fertility, which hurts rural populations' livelihoods in developing countries. Environmental conditions during the hot season cause modifications in the oestrous cycle and endocrine secretions so that there is reduction in the fertility. In addition, there is decrease in small (3–5 mm) and medium sized (6–9 mm) follicular population by causing changes in follicular dynamics which in turn influence the follicular steroid production and subsequently reduction in the diameter of the dominant follicle. Furthermore, high temperatures and humidity may influence the quality of oocytes by premature aging, disparity in nuclear to cytoplasmic maturation and development of the embryos both in vivo or in vitro. The harmful consequences of HS begin with the developing egg and continue to the subsequent stages i.e., the oestrus cycle and oestrus behaviour; the development and implantation of the embryo, the uterine environment and even the growing foetal calf. Therefore, the micro-environment of oocytes development is a cue for the success of in vitro maturation, embryo development and fertility. Reducing the impact of heat stress on oocyte quality, competence, and fertility in cattle has been achieved through nutritional management, breeding management, genetic selection of more heat-tolerant heifer breeds, hormonal manipulation with timed AI, nutritional manipulation, antioxidant treatment, and other measures.