Luteal activity at the onset of a timed insemination protocol affects reproductive outcome in early postpartum dairy cows.

This study was designed to compare two timed insemination protocols, in which progesterone, GnRH and PGF2alpha were combined, with the Ovsynch protocol in presynchronized, early postpartum dairy cows. Reproductive performance was also evaluated according to whether cows showed high or low plasma progesterone concentration, at the onset of treatment. One hundred and six early postpartum dairy cows were presynchronized with two cloprostenol treatments given 14 days apart, and then assigned to one of the three treatment groups. Treatments for the synchronization of estrus in all three groups started 7 days after the second cloprostenol injection, which was considered Day 0 of the actual treatment regime. Cows in the control group (Ovsynch, n=30) were treated with GnRH on Day 0, PGF2alpha on Day 7, and were given a second dose of GnRH 32 h later. Cows in group PRID (n=45) were fitted with a progesterone releasing intravaginal device (PRID) for 9 days, and were given GnRH at the time of PRID insertion and PGF2alpha on Day 7. In group PRID/GnRH (n=31), cows received the same treatment as in the PRID group, but were given an additional GnRH injection 36 h after PRID removal. Cows were inseminated 16-20 h after the administration of the second GnRH dose in the Ovsynch group, and 56 h after PRID removal in the PRID and PRID/GnRH groups. Ovulation rate was determined on Day 11 postinsemination by detecting the presence of a corpus luteum in the ovaries. Lactation number, milk production, body condition at the onset of treatment and treatment regime were included as potential factors influencing ovulation and pregnancy after synchronization. Logistic regression analysis for cows with high and low progesterone concentration on treatment Day 0 revealed that none of the factors included in the models, except the interaction between progesterone and treatment regime, influenced the risk of ovulation and pregnancy significantly. In cows with high progesterone concentration at treatment onset, Ovsynch treatment resulted in a significantly improved pregnancy rate over values obtained following PRID or PRID/GnRH treatment. In cows with low progesterone concentration, PRID or PRID/GnRH treatment led to markedly increased ovulation and pregnancy rates with respect to Ovsynch treatment. These findings suggest the importance of establishing ovarian status in early postpartum dairy cows before starting a timed AI protocol, in terms of luteal activity assessed by blood progesterone.