Artificial insemination outcomes in beef females using bovine sperm with adetectable fertility-associated antigen

In this study, semen samples from 25 bulls that had passed a breeding sound ness evaluation were analyzed for the presence or absence of a 31-kDa prote in, known as fertility-associated antigen (FAA), on spermatozoal membranes. Eighteen bulls had FAA on sperm (FAA-positive) and seven were devoid of FA A on sperm (FAA-negative). A single ejaculate from each bull was extended a nd frozen with 25 to 30 x 10(6) sperm in .5-mL straws. Crossbred replacemen t heifers (n = 865) were estrus-synchronized and artificially inseminated e ither at timed AI or 12 h after they were detected in estrus. Mature cows ( n = 285) were inseminated 12 h after they were detected in estrus during a 45-d AI period. Pregnancy rates (pooled) to first AI service for females (n = 764) inseminated with FAA-positive sperm were 65.6% and were 49.7% for f emales (n = 386) inseminated with FAA-negative sperm (P < .005). Among the estrus-synchronized replacement heifers, pregnancy rates to synchronized Al service for heifers (n = 550) inseminated with FAA-positive sperm were 62% and were 45.7% for heifers (n = 315) inseminated with FAA-negative sperm ( P < .005). These data indicate that pregnancy rates to first Al service at spontaneous and synchronized estrus are higher when using semen from bulls with detectable FAA on spermatozoal membranes compared to semen from bulls devoid of FAA on membranes. Fertility-associated antigen is an important de terminant for fertility potential of sperm from bulls to be used in Al bree ding programs.