Effect of environmental thermal stress on reproductive performance of Holstein cows in Egypt

The aim was to investigate effects of ambient temperature-humidity index (THI) on the reproductive indices of 920 Holstein (HO) cows in the subtropics. THI was categorized as low: below 70; moderate: from 70 to 75 and high: more than 75. The high THI significantly (P < 0.001) prolonged the periods of calving interval, days open and dry period, and increased the service per conception rate. The conception rate in the high THI group (17.31%) was significantly (P < 0.001) lower than that noticed in both low (36.96%) and moderate THI (31.61%) groups. Meanwhile, high THI significantly increased the embryonic loss (P < 0.001) and abortion (P=0.043) rates compared with low (14.62% and 8.89%; respectively) and moderate (22.84%; and 11.17%; respectively) THI groups. The high THI group had a significantly (P=0.001) greater embryonic losses than the other groups. Conclusively, THI over 75 deteriorates the reproductive indices of Holstein cows.