Effect of egg yolk levels on the fertility of diluted bovine sperm stored at ambient temperatures

There were no significant differences in fertility between semen diluted in Caprogen and stored at ambient temperatures with egg yolk levels of 20, 5,2, and 1%. There was, however, a highly significant interaction between sires and egg yolk concentrations in a trial comparing 5, 2, and 1 % egg yolk. This effect resulted from reducing egg yolk level with semen of one sire. Reducing egg yolk level for this sire from 5 to 2% and 5 to 1 % lowered the 49‐day nonreturn rate by 5.8 and 17.1 %, respectively. Possible reasons for sire differences are discussed.