According to initial research findings, the timing of insemination affects the ratio of bull calves to heifer calves.
Preliminary data from Richard Pursley, extension dairy reproductive specialist at Michigan State University, show that inseminating cows 36 hours before ovulation results in 65 percent heifers. And, insemination at 16 hours before ovulation results in 56 percent heifers. The industry average is 46 percent heifers and 54 percent bulls.
When sperm is in the reproductive tract longer, it appears that more of the x-chromosomes succeed in fertilizing the egg.
Still, Pursley says it is too soon to change your insemination strategy. The study will be completed by the first of the year.