Heat stress and seasonal effects on reproductive performance and milk production in dairy cows raised in hot and humid climate

Abstract

The effects of heat stress and utilizing evaporative cooling, equipped with tunnel ventilation, on postpartum reproductive performance and the milk production of early dictating dairy cows in a hot and humid climate, were studied from April 2004 to May 2005. Thirty-six crossbred. Holstein-Friesian (93.75%HF), primiparous cows were randomly assigned to one of two groups, based upon calving date and body weight. Cooled cows (n=18; treatment) were housed in a tunnel ventilated barn equipped with an evaporative, cooling pad system and uncooled cows (n=18; control) were housed in a naturally ventilated barn without a supplemental cooling system. The temperature, relative humidity, rectal temperature and respiration rates were continuously monitored and recorded at the AM and PM milkings. Cows were milked twice daily and fed a totally mixed ratio (TMR), ad libitum. Daily feed intake and milk production were recorded. Evaporative cooling and tunnel ventilation systems reduced (P<0.05) the afternoon barn temperature and the conditions of heat stress in the dairy cows. Cooled cows had lower(P<0.05) rectal temperatures and respiration rates than the uncooled cows. Cooled cows had greater (P<0.05) dry matter intake and milk production than the uncooled cows. There was no significant difference in the postpartum anovular condition and interval to first postpartum ovulation between the cooled and the uncooled cows. In addition, there was no difference between the groups for follicular development after the synchronization of oestrus, and the days from PGF 2 α infection to ovulation. However, the synchronization rates and conception rates in the cooled cows tended to be greater than in the uncooled cows. The benefits were demonstrated by increased income over costs. These results suggest that heat stress has a significant impact on postpartum reproductive performance and milk production, and evaporative cooling and tunnel ventilation systems have the potential to decrease heat stress, alleviate the symptoms of heat stress and improve both milk production and metabolic efficiency, during early lactation, without affecting reproductive function in dairy cows in hot and humid climates.