Timed artificial insemination with estradiol cypionate or insemination at estrus in high-producing dairy cows

A total of 799 Holstein cows from 3 herds were randomly assigned at 37 +/- 3 d in milk ( DIM) to timed artificial insemination ( AI) or insemination at detected estrus. Cows were presynchronized with injections of PGF(2alpha) at 37 and 51 DIM. At 65 DIM, cows received an injection of GnRH, followed 7 d later by PGF2a. Cows in the estrus-detected group were inseminated after being observed in estrus during the 7 d after the last PGF2a. Cows in the timed AI group received an injection of 1 mg of estradiol cypionate (ECP) 24 h after the last PGF(2alpha). If detected in estrus less than or equal to24 h after ECP, cows were inseminated then or at a fixed time 48 h after ECP. Pregnancy was diagnosed by ultrasonography at 30 d and by palpation at 44 and 58 d after AI. Plasma progesterone was measured in 4 samples per cow collected on days of 1) second PGF2a, 2) GnRH, 3) third PGF2a, and 4) 48 h after third PGF2a. Cows were classified as cyclic or anovulatory based on progesterone concentrations in samples 1 and 2. Similarly, cows were classified according to progesterone concentrations in samples 2, 3, and 4 ( H = greater than or equal to 1 ng/mL; L = < 1 ng/mL), resulting in 8 combinations (LLL, LHL, LLH, LHH, HHH, HHL, HLH, and HLL). Conception rates and pregnancy rates were higher for cows in the timed AI group than in the estrus-detected group at 30, 44, and 58 d ( e. g., at 58 d, pregnancy rates were 42.2% for multiparous cows or 34.4% for primiparous cows in the group receiving ECP and timed AI compared with only 20.8 or 18.8% for respective parity subgroups for the treatment group inseminated only at detected estrus). Pregnancy losses were 11.5% from 30 to 58 d and did not differ between treatments. Cyclic cows within both treatments had higher estrous responses, conception rates, and pregnancy rates. Cows that responded to presynchronization and to luteolysis ( HHL) had the highest conception and pregnancy rates, followed by cows classified as LHL. Use of 1 mg of ECP to induce ovulation as part of a synchrony regimen improved reproduction at first postpartum insemination in dairy cows.