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 (<i>P</i> < 0.01) pregnancy at first AI (P/AI; 55.3%) than multiparous cows (MPC; 38.6%). But PPC submitted to SP had the greatest P/AI during the cold season (63.8%), followed by PPC on SP (57.5%) and on HD (54.6%) during the hot season. During the cold season, P/AI in PPC on HD was lower (45.6%) than that of PPC on SP (63.8%); whereas P/AI in MPC was similar among treatments and seasons, except for MPC in HD during the hot season (32.2%) compared with those on SP (41.9%). By 150 DIM, there were no differences in the proportion of pregnant cows between SP and HD. Cows with retained placenta tended to be inseminated later than those that expelled the placenta within 24 h. Cows that experienced metritis tended to have lower P/AI than cows that stayed healthy after calving, but cows on SP that incurred metritis tended to have better P/AI than cows on HD with metritis. Relying on estrus detection may allow for a first AI at lower DIM, but at 150 DIM, the proportions of pregnant cows was similar between the 2 strategies.