Relationship of Temperature and Humidity to Conception Rate of Holstein Cows in Subtropical Climate

Conception rates of a Holstein dairy herd near Culiacan on the west coast of Mexico were evaluated with respect to the average temperature-humidity index of the 2 days prior to breeding, the day of breeding, and the day following breeding. Average daily index for 3 yr ranged from 62 to 86. Average daily ambient temperature and relative humiditv for indexes 76 and 82 were 26.5 C," 68% and 29.7 C, 75%. Conception rates for 191 cows serviced on days with an average index under 66 was 67% as compared to 21% for 818 cows serviced on days averaging above 76. The average temperature-humidity index of the 2nd day prior to breeding was the most related to conception rate. Conception rate declined from 55 to 10% as the average index of this day increased from 70 to 84 (r = --.995). Between 68 and 82 the average conception was 42.3% ff the average index of the 2 days prior to breeding was less than on the day of breeding. Conception rates averaged 10.4% lower (31.9%) ff the index of the 2 days prior to breeding was higher than on the day of breeding indicating that temperature~humidity of individual days prior to breeding influenced breeding efficiency.