CO-Synch enhances time to ovulation, cyclicity and pregnancy in anovulatory lactating Bos taurus/Bos indicus cows

Induction of ovulation for timed artificial insemination (TAI) was evaluated in postpartum anovulatory and lactating Bos taurus/Bos indicus cows (n = 50). Palpation per rectum and transrectal ultrasonography were used on days − 30, − 20, − 10 and 0 (day 0 = start of treatment) to confirm the anovulatory status but with ovarian follicles ≥ 10 mm on day 0, and on the days of PGF2α injection and pregnancy diagnosis to determine rates of ovulation and induction of cyclicity. Cows were randomly assigned to: (1) CO-Synch (n = 25; day 0, 200 μg GnRH; day 7, 150 μg PGF2α; day 9, 200 μg GnRH + TAI) and (2) control (n = 25; no treatment). Rates of ovulation for the first GnRH injection, pregnancy and cyclicity induction were greater for CO-Synch (P < 0.05). There was no effect of body condition score (BCS) (P > 0.05). In conclusion, the CO-Synch protocol resulted in acceptable rates of cyclicity induction and pregnancy to TAI in anovulatory and lactating B. taurus/B. indicus cows under tropical conditions.