Efficacy of an intravaginal progesterone insert and an injection of PGF(2 alpha) for synchronizing estrus and shortening the interval to pregnancy inpostpartum beef cows, peripubertal beef heifers, and dairy heifers

The objective was to test the efficacy of an intravaginal progesterone inse rt and injection of PGF(2 alpha) for synchronizing estrus and shortening th e interval to pregnancy in cattle. Cattle were assigned to one of three tre atments before a 31-d breeding period that employed artificial insemination . Control cattle were not treated, and treated cattle were administered PGF (2 alpha) or an intravaginal progesterone-releasing insert (CIDR) for 7 d a nd treated with PGF(2 alpha) 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 acti vity before treatment was determined for individual cattle based on blood p rogesterone concentrations. In Exp. 1, there was a greater incidence of est rus during the first 3 d of the breeding period in CIDR+PGF(2 alpha)-treate d cows compared with PGF(2 alpha)-treated or control cows (15, 33, and 59% for control, PGF(2 alpha), and CIDR+PGF(2 alpha), 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, PGF(2<alpha>), and CIDR+PGF(2 a lpha), respectively; P < 0.001) and tended to improve pregnancy rate for th e 31-d breeding period for cows treated with CIDR+PGF(2<alpha>) (50, 55, an d 58% for control, PGF(2 alpha), and CIDR+PGF(2 alpha), respectively, P = 0 .10). Improvements in rates of estrus and pregnancy after CIDR+PGF(2 alpha) were also observed in beef heifers. Presence of luteal activity before the treatment period affected synchronization and pregnancy rates because anes trous cows (Exp. 1) or prepubertal heifers (Exp. 2) had lesser synchronizat ion rates and pregnancy rates during the first 3 d of the breeding period a s well as during the entire 31-d breeding period. The PGF(2 alpha) and CIDR +PGF(2 alpha), but not the control treatments were evaluated in dairy heife rs (Exp. 3). The CIDR+PGF(2 alpha)-treated heifers had a greater incidence of estrus (84%) during the first 3 d of the breeding period compared with t he PGF(2 alpha)-treated heifers (57%), but pregnancy rates duping the first 3 d or during the 31-d breeding period were not improved for CIDR+-PGF(2 a lpha) compared with PGF(2 alpha)-treated heifers. In summary, the concurren t treatment of CIDR and PGF(2 alpha) improved synchronization rates relativ e to PGF(2 alpha) alone or control. Improved estrus synchrony led to greate r pregnancy rates for beef cows and beef heifers but failed to improve preg nancy rates for dairy heifers.