The effect of artificial insemination once versus twice per day.

The objective of this study was to determine the effect of inseminating Jersey cows and heifers once per day or according to the a.m.-p.m. rule. A total of 337 artificial inseminations (AI) were completed by three technicians at the University of Tennessee Dairy Experiment Station at Lewisburg for 6 mo. Cows and heifers were inseminated at estrus using the a.m.-p.m. rule on even days of the month. On odd days of the month, AI were once daily between 0800 and 1200 h. Estrus detection was conducted two to three times daily. Pregnancy was confirmed by rectal palpation 60 to 80 d after AI. Herd DHIA averages were a 12.2-mo calving interval, 76 d to first AI, 83% observed estruses, and a 50% conception rate during the trial. Pregnancy data were analyzed with a model including treatment, AI, lactation number, parity, technician, and group. This study grouped cows and heifers according to when they were in estrus and inseminated (a.m.-a.m., a.m.-p.m., or p.m.-a.m.); means were 43.7, 57.9, and 59.0%, respectively. The a.m.-p.m. AI versus once per day AI yielded a pregnancy rate of 55.6% versus 51.3%. These results show no difference among Jersey cows or heifers that were inseminated artificially once daily in the a.m. However, those cows and heifers inseminated in the a.m. of first estrus detection had a lower pregnancy rate.