Fertility of postpartum dairy cows generally decreases during summer when compared to winter seasons. The important factor behind the decrease in fertility is increase in ambient temperature that results in reduced levels of fertility hormones especially LH (Luteinizing Hormone) and estradiol due to direct effect of heat stress on hypothalamus in the brain. Heat stress also acts on ovary and uterine environment, which creates unfavorable condition to the oocytes and embryo. In addition, heat stress also causes decrease in dry matter intake, which in turn leads to negative energy balance. This also affects the levels of fertility hormones. To overcome these situations, measures like providing cooling system for animals, providing adequate drinking water and providing high quality forage and feed may help and improve the fertility in animals.
Compiled by Dr S Raja, NDDB from F D Rensis, R J Scaramuzzi /Theriogenology 60(2003) 1139-1151