Effect of heat stress on incidence of retained placenta in Holstein cows at dry hot weather of Shiraz

To study the heat stress effect on the incidence of retained placenta in dry and hot weather of Shiraz, five hundred and forty two Holstein cows were examined. The study revealed that incidence of retained placenta was 6.92, 18.3, 13.23 and 7.58% in spring, summer, fall and winter, respectively. The average temperature-humidity index (THI) was 73.2 in summer, indicating that the cows were under heat stress. It is concluded that heat stress increased the incidence of retained placenta in Holstein cows.