20 years ago, before sexed semen I presume, I synchronized seven 3 year old cows, all were AId the same day to GR Exclusive and GR Dreamboat. All stuck and all had bull calves from 4 days early to 10 days late. In 45 years of raising Shorthorns, this is the first year I can remember having more heifers than bulls and the ratio is better than 3 to 1. I've had 12 year old cows that have never had a heifer calf. The general rule of thumb is the more you want a heifer, the greater the odds you'll get a bull. (and in Shorthorns, you'll probably get a white, horned one at that!)