Efficacy of an intravaginal progesterone insert and an injection of PGF2α for synchronizing estrus and shortening the interval to pregnancy in postpartum beef cows, peripubertal beef heifers, and dairy heifers1

The objective was to test the efficacy of an intravaginal progesterone insert and injection of PGF2α for synchronizing estrus and shortening the interval to pregnancy in cattle. Cattle were assigned to one of three treatments before a 31-d breeding period that employed artificial insemination. Control cattle were not treated, and treated cattle were administered PGF2α or an intravaginal progesterone-releasing insert (CIDR) for 7 d and treated with PGF2α on d 6. The treatments were applied in one of three experiments that involved postpartum beef cows (Exp. 1; n = 851; 56 ± 0.6 d postpartum), beef heifers (Exp. 2; n = 724; 442.5 ± 2.8 d of age), and dairy heifers (Exp. 3; n = 260; 443.2 ± 4.5 d of age). Luteal activity before treatment was determined for individual cattle based on blood progesterone concentrations. In Exp. 1, there was a greater incidence of estrus during the first 3 d of the breeding period in CIDR+PGF2α-treated cows compared with PGF2αtreated or control cows (15, 33, and 59% for control, PGF2α, and CIDR+PGF2α, respectively; P < 0.001). The improved estrous response led to an increase in pregnancy rate during the 3-d period (7, 22, and 36% for control, PGF2α, and CIDR+PGF2α, respectively; P <