Heat stress impact on the dairy cattle fertility

Abstract

The increase of the ambient temperature has a negative effect; it is altering the physiology of the reproductive system of the cow including the oocyte, granulose and the theca cell, the developing embryo during the early stages of development, and the quality of the sperm . The low LH and estradiol is one of the main factors for low fertility during the hot weather. The decrease of FSH and the low concentration of inhibin decrease the quality of the preovolatory follicle and therefore the fertility. The primary site affected by heat stress seems to by the hypothalamic axis. There are two ways how heat stress affects the bovine animal and decreases fertility: The first is before conception, the animal fails to enter into estrus due to immature follicle or hormonal alteration affecting the Oestrus cycle, or during heat stress the Estrus behavior is weak. The second way is after conception, showing that heat stress has a high effect on the first days of the embryonic development. The high rectal temperatures of the animal have direct negative effect and indirect effect on the hormones responsible to sustain the pregnancy.