Analysis of cow factors influencing conception rates after two timed breeding protocols

The objective of this study was to determine cow factors that influence con ception rates after timed artificial insemination (TAI) on a commercial dai ry farm. In Trial 1, 197 cows were synchronized by an administration of 25 mg of dinoprost between Days 48 and 54 post partum and again 14 days later. Cows were inseminated 66 and 90 hours after the second treatment. In Trial 2, 196 cows were treated with an Ovsynch protocol consisting of an adminis tration of 0.02 mg of buserelin between Days 62 and 68 post partum, a treat ment with 0.75 mg of tiaprost 7 days later and a second treatment with buse relin 48 h later. Cows were bred 16 to 20 hours after the last treatment. C ows with abnormal vaginal discharge at the time of insemination were exclud ed from AI. Lactation number, milk yield, fat and protein content of milk, signs of endometritis at an examination 14 to 20 days post partum and month of breeding were included as potential factors influencing conception on T AI. Conception rates after timed breeding were 32.0% and 30.6% in Trials 1 and 2, respectively. Logistic regression revealed that neither milk product ion parameters nor endometritis at post partum. examination influenced conc eption rates in either of the two timed breeding protocols. Only parity sho wed an effect (P=0.012) in Trial 2. Primiparous cows were more likely to co nceive after timed breeding than older cows (43.5 vs. 23.1%). An effect of parity, however, was not observed in Trial 1. It can be concluded that neit her milk production nor endometritis at an examination 14 to 20 days post p artum influence conception rates after TAI if cows with abnormal vulval dis charge at the designated time of Al are excluded from breeding. (C) 2001 by Elsevier Science Inc.