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Reproductive Performance of Lactating Dairy Cows after Resynchronization with Ovsynch or a Program Aimed to Maximize Artificial Insemination in Estrus and Fertility of Timed Artificial Inseminations based on Ovarian Structures
Our objective was to compare the reproductive performance of dairy cows after enrollment in a program that combined resynchronization with Ovsynch and AI in estrus based on activity (AIAct) versus a program aimed to maximize AIAct and fertility of timed AI (TAI) services by assigning treatments according to the ovarian structures present at non-pregnancy diagnosis (NPD). One day after NPD by transrectal ultrasonography at 31±3 d after AI, lactating cows were blocked by parity (primiparous vs. multiparous) and randomly assigned to: 1) Control (CON; n=469): resynchronization with Ovsynch-56 (GnRH-7d-PGF-56h-GnRH-16h-TAI) at 32±3 d after AI combined with AIAct or 2) Treatment (TRT; n=430): cows with a corpus luteum (CL) ≥20 mm (TRT-CL) received a PGF injection and AIAct for 9 d. Cows with no CL or CL <20 mm (TRT-NoCL) received a GnRH injection 2 d after enrollment. Cows in TRT-CL and TRT-NoCL not AIAct were enrolled in a 5d-Ovsynch+Progeterone protocol (GnRH+CIDR-5d-PGF+CIDRremoval-1d-PGF-32h-GnRH-16h-TAI) 9 and 7 d after the PGF or GnRH injection, respectively. The percentage of cows with a CL ≥20 mm at NPD was similar (P=0.79) for CON (64.2%; 301/469) and TRT (63.3%; 272/430) whereas, it was greater (P=0.005) for multiparous than primiparous cows (66.8 vs. 57.1%). Cows in CON (mean 9.5 d, median 10 d) were reinseminated at a faster rate (P<0.01; HR 2.9 CI: 2.4-3.5) than cows in TRT (mean 13.2 d, median 17 d). Parity did not affect (P=0.76) time to reinsemination. After enrollment, a greater (P<0.001) percentage of cows received AIAct in TRT (29.8%) than CON (10.4%) whereas, a greater (P<0.001) percentage of cows were AIAct in TRT-CL (38.6%) than TRT-NoCL (14.6%). Pregnancies per AI (P/AI) for cows AIAct were similar (P=0.65) for CON (32.7%; 16/49) and TRT (28.8%; 36/125) and were not affected by parity (P=0.37). Also, P/AI after TAI were similar (P=0.47) for CON (27.9%; 113/405) and TRT (30.4%; 87/286) and were not affected by parity (P=0.55). Pregnancy rate from 0 to 21 d after enrollment was similar (P=0.62) for CON (28.4%; 129/454) and TRT (29.9%; 123/411). Thus, compared to a typical resynchronization program, a program aimed to maximize AIAct and fertility of TAI by assigning treatments according to ovarian structures; increased the percentage of cows AIAct and had similar pregnancy rate by 21 d after NPD, however, time to reinsemination was delayed which could be explained by the small percentage of cows inseminated on activity.
Keywords:
Resynchronization
Estrous activity
Dairy Cow