Effect of acrosomal defects on fertility of bulls used in artificial insemination and natural breeding

Four bulls that produced spermatozoa with a high percentage of abnormal acr osomes were individually placed in pens with females for 21 days. Frozen se men from 2 of the bulls was used for artificial insemination. One of the bu lls was placed in a competitive mating situation with normal bulls at pastu re. First service pregnancy rates were determined by transrectal ultrasonog raphy 28 days after bull removal from breeding pens, or after the last arti ficial insemination. The results of competitive mating at pasture were dete rmined from breeding observations, the phenotypic characteristics of calves sired, and blood typing for parentage. The results of these studies sugges t that bulls that produce a high percentage of spermatozoa with indented ac rosomes may have normal fertility when used in artificial insemination or i n single sire mating; however, their fertility may be low when breeding com petitively with bulls with normal spermiograms.