Record the cow's number and the breeding date in your pocket calendar and check that cow closely for any signs of return heat 18-23 days later. If the percentage of cows returning to heat is high, remove the bull and check for injury or semen quality factors. Replace the questionable bull with a fresh bull. In a multi-sire breeding system, the infertile or sterile bull often goes unnoticed because another bull will get the cow bred. Do not mix bulls or unequal rank .
Older bulls are usually more dominant and often have lowered fertility.
Dominance and sex drive are not related, and neither is dominance and fertility. In multi-sire groups, pregnancy rates can be reduced when the dominant bull is infertile. Use homogenous groups of younger bulls. In an ideal world, all breeding herds would be single-sire. Ideal because sire identity as well as fertility would be known.