Presynchronization strategy using prostaglandin F2α, gonadotropin-releasing hormone, and detection of estrus to improve fertility in a resynchronization program for dairy cows.

Objectives of experiment 1 were to evaluate pregnancy outcomes and reinsemination patterns of cows whose estrous cycles or ovulation were presynchronized with prostaglandin (PGF2α) or PGF2α and gonadotropin-releasing hormone (GnRH) after non-pregnancy diagnosis in programs focusing on inseminating cows based on tail paint removal. Objectives of experiment 2 were to evaluate pregnancy outcomes and reinsemination patterns of cows with or without a corpus luteum (CL) present at non-pregnancy diagnosis in a program utilizing PGF2α and GnRH to presynchronize estrous cycles before resynchronization. Lactating Holstein cows from three herds were enrolled in the experiments at non-pregnancy diagnosis (d 0). Estrus was determined daily based on tail paint removal. In experiment 1, cows were assigned randomly to two treatments: (1) PGF2α on d 0 (n = 967; P7); and 2) PGF2α on d 0 and GnRH on d 7 (n = 962; P7G7). Cows not reinseminated based on tail paint removal were submitted to the timed-AI Cosynch-72 protocol 7 d after presynchronization treatments. Pregnancy per AI (P/AI) was greater (P = 0.01) for P7G7 cows than P7 cows. Cows inseminated based on tail paint removal had increased (P < 0.01) P/AI than cows submitted to the timed AI protocol. In addition, an interaction was detected (P = 0.03) between method of insemination and presynchronization treatment such that cows submitted to timed AI in the P7G7 treatment had greater P/AI than P7 cows. Nonetheless, P7 cows were inseminated at a faster rate (P < 0.01) than P7G7 cows. In experiment 2, presence of a CL was determined by transrectal ultrasonography at initiation of the P7G7 protocol (n = 1479). In a random subset of cows (n = 210), blood samples were collected immediately after ultrasound examination to determine progesterone concentration in order to evaluate accuracy of detection of a CL by ultrasonography. Accuracy of detection of a CL was 80%. Hazard to insemination and P/AI did not differ among cows regardless of CL status. In conclusion, herds relying mostly on detected estrus to reinseminate cows may achieve greater pregnancy outcomes if presynchronizing with PGF2α and GnRH instead of only PGF2α, albeit at a slower insemination rate. In addition, pregnancy outcomes and reinsemination patterns were similar for cows bearing or not bearing a CL when utilizing the P7G7 protocol, indicating a limited benefit of evaluating ovarian luteal structures by ultrasonography.