A total of 1,421 lactating dairy cows on 4 spring-calving farms were stratified based on days in milk (DIM) and parity and randomly allocated to 1 of 3 treatments: (1) control: no hormonal treatment; cows inseminated at detected estrus; (2) P4- Ovsynch: cows received a 7-d P4-releasing intravaginal device with 100 μg of a gonadotropin-releasing hormone analog at PRID insertion, a 25-mg injection of PGF2α at PRID removal, GnRH at 56 h after device removal and TAI 16 h later; (3) P4-Ovsynch+eCG: the same as P4-Ovsynch, but cows received 500 IU of equine chorionic gonadotropin at PRID removal.