Time of Artificial Insemination and Fertility in Dairy Cattle

Data were from 44,707 cows and first-calf heifers in a commercial artificial insemination program.The percentage of heifers first seen in estrus in the morning was 73.2, not different from 72.6 for cows.Unfrozen semen was used for insemination.The 150-to 180-day percent nonreturns for cows inseminated before noon the same day (67.1) was not different from those inseminated between noon and 1800 h (69.9) and after 1800 h (68.9) the same day.However, insemination the following morning was too late for best results (62.7%).Cows first seen in estrus in the evening should be inseminated by noon the next day.The nonreturn rate for cows inseminated after 1400 h the next day resulted in 63.8% 150-to 180-day nonreturns.A single mid-morning insemination for all cows first seen in estrus the night before or the same morning should give near maximum conception.