Reproductive performance of dairy cows assigned to either a combination of estrus detection using sensors and timed artificial insemination or to a synchronization program.

At calving, 2,213 Holstein cows from 5 farms were enrolled in a study to establish potential associations between postcalving health disorders and reproductive performance and to determine the effectiveness in achieving pregnancy at first artificial insemination (AI) and the consequences on the proportion of cows pregnant by 150 DIM when using 2 different reproductive management programs for first service. Within farm, cows were randomly allocated to 2 reproductive schemes: (1) inseminating based on estrus detection with a backup synchronization program (SP) on open cows with DIM ≥ 80 (HD; 1,141 cows, 34% primiparous [PPC]) or (2) after an SP (1,072 cows, 35% PPC). Cows on HD were inseminated when detected in estrus using an accelerometer if DIM >50, and those not inseminated based on estrus by 80 ± 3 DIM (28.8%) were submitted to an Ovsynch protocol, if a corpus luteum (CL) was present, or to the same Ovsynch protocol but with the addition of a progesterone-releasing intravaginal device if CL was absent. Cows on SP were submitted to a simplified double-Ovsynch protocol (the first GnRH injection was omitted) and serviced between 74 and 80 DIM. On average, cows on HD were first inseminated at 72.4 ± 1.63 DIM, whereas those on SP were first inseminated at 78.3 ± 1.63 DIM. At first AI, PPC had a greater (