| Abstrakt: |
Two experiments examined pregnancy after synchronized ovulation (Ovsynch) with or without progesterone (P4) administered via controlled internal drug release (CIDR) intravaginal inserts. In experiment 1, 262 lactating cows in one herd were in 3 treatments: Ovsynch (n = 91), Ovsynch + CIDR (n = 91), and control (n = 80). The Ovsynch protocol included injections of GnRH 7 d before and 48 h after an injection of PGF20. Timed artificial insemination (TAI; 57 to 77 d postpartum) was 16 to 20 h after the second GnRH injection. Cows in the Ovsynch + CIDR group also received a CIDR (1.9 g of P4) insert for 7 d starting at first GnRH injection. Control cows received A-I when estrus was detected using an electronic estrus detection system. Based on serum P4, 44.1% of cows were cyclic before Ovsynch. Pregnancy rates at 29 d (59.3 vs. 36.3%) and 57 d (45.1 vs. 19.8%) after TAI and embryo survival (75.9 vs. 54.5%) from 29 to 57 d were greater for Ovsynch + CIDR than for Ovsynch alone. In experiment 2, 630 cows in 2 herds received TAI at 59 to 79 d postpartum after 6 treatments. Estrous cycles were either presynchronized (2 injections of PGF2alpha 14 d apart; n = 318) or not presynchronized (n = 312). Within those groups, Ovsynch was initiated 12 d after second presynchronization PGF2alpha, and used alone (n = 318) or with CIDR inserts for 7 d (1.38 g of P4/insert, n = 124 or 1.9 g of P4/insert, n = 188). Before Ovsynch, 80% of cows were cyclic. Presynchronization increased pregnancy (46.8 vs. 37.5%) at 29 d after TAI, but CIDR inserts had no effect on pregnancy in experiment 2. Overall embryonic survival between 29 and 57 d in experiment 2 was 57.7%. Use of CIDR inserts with Ovsynch improved conception and embryo survival in experiment 1 but not in experiment 2, in part due to differing proportions of cyclic cows at the outset. Presynchronization before Ovsynch enhanced pregnancy rate. |
