Effect of estrus expression prior to ovulation synchronization protocols on reproductive efficiency of lactating dairy cow

Cosynch-72 (CO-72) is one of the most widely known timed AI (TAI) protocols in cattle. The protocol involves giving GnRH on d-7, PGF2α on day 0, and the second GnRH on day 3 concurrent with AI. CO-72 has been adapted as the standard reproductive management protocol in postpartum (pp) dairy cows in several large dairy farms in Jordan. This research was conducted to study the effect of estrus detection and presynchronization strategy prior to Cosynch protocol on reproductive efficiency of lactating dairy cows in Jordan. Cows (n=1220) were injected with PGF2α on day 30±3 pp and observed for signs of estrus over the experiment. Cows detected in estrus before (n=21) or after (n=409) PGF2α injection underwent to CO-72 protocol starting with GnRH 12 days after heat (control group; HCO-72). In contrast, cows that were not detected in estrus were randomly assigned into two treatments (NHCO-72; NHOV-CO-72): cows in the NHCO-72 treatment underwent a CO-72 protocol on day 44±3 pp; while cows in the NHOV-CO-72 treatment underwent a first CO-72 protocol without AI starting on day 44±3 followed by another CO-72 protocol with AI seven days after the last GnRH injection (day 61±3). Cows showed premature estrus (≤48 h post-PGF2α) (n=184) were excluded from the study. Cows in NHOV-CO-72 treatment had higher (P<0.05) pregnancies per AI (P/AI) and reduced pregnancy losses (PL) (42.8, 14.5%) than those in HCO-72 (27.1, 43.0%) and NHCO-72 (26.8, 42.5%) treatments, respectively. Pregnancies per AI and PL were significantly (P<0.05) affected by parity and season. Primiparous had higher P/AI and reduced PL (35.4, 21.4%) than multiparous cows (28.7, 41.7%; respectively). Cows inseminated in cold months had higher P/AI and reduced PL (35.9, 17.9%) than cows inseminated in hot months (24.8, 52.9%; respectively). In conclusion, presynchronization in the NHOV-CO-72 treatment increased P/AI and reduced PL when compared to the other two treatments. Detection of estrus before the beginning of Cosynch did not affect fertility and cows exhibiting heat at any time during the synchronization protocol should be inseminated to maximize P/AI. Improvement in the NHOV-CO-72 in this study was probably due to later insemination and not for induction of cyclicity as there were no differences between HCO-72 and NHCO-72.