A reproductive management program aimed at increasing reinsemination of nonpregnant dairy cows at detected estrus resulted in similar reproductive performance to a program that favored timed artificial insemination

摘要

The objective of this experiment was to compare timeto pregnancy and proportion of cows not pregnant 210d after first service for cows managed for second andsubsequent artificial insemination (AI) services with areproductive management program that promoted reinseminationat detected estrus (AIE) or a program thatpromoted timed AI (TAI). After first service, lactatingHolstein cows were blocked by parity and randomlyassigned to d 32 Resynch (D32R; n = 464) or AIEResynch (AIER; n = 512). To determine the effect ofmanagement strategies on time to pregnancy and cowsnot pregnant by the end of a 210 d at-risk period afterfirst AI service, cows remained in AIER and D32Runtil pregnancy or herd exit. Cows in D32R receiveda GnRH treatment 32 ± 3 d after AI (first treatmentintervention; FTI). Nonpregnancy diagnosis was conducted7 d later by transrectal ultrasonography whennonpregnant cows with a corpus luteum (CL) ≥15 mmcompleted the Resynch protocol (PGF_(2α), 56 h laterGnRH, and 16 to 18 h later TAI) and cows withouta CL (NoCL cows) were enrolled in a PreG-Ovsynchprotocol (GnRH, 7 d later GnRH, 7 d later PGF_(2α), 56h later GnRH, and 16 to 18 h TAI) to receive TAI. Forthe AIER treatment, nonpregnant cows with a CL ≥15mm observed by transrectal ultrasonography 32 ± 3 dafter AI (i.e., FTI) received PGF_(2α) to induce estrus.Cows not AIE within 7 d were enrolled in Resynch(GnRH, 7 d later PGF_(2α), 56 h later GnRH, and 16to 18 h TAI). Cows in the NoCL group in AIER wereenrolled in PreG-Ovsynch. Detection of estrus was performedbased on visual observation of behavioral signsof estrus and tail-paint removal. Binomial data wereanalyzed with logistic regression and time to eventdata with Cox’s proportional regression. After the FTI,a greater proportion of cows were AIE in AIER thanD32R (36.0 vs. 11.9%) and more cows were AIE within7 d of the FTI for AIER (25.0%) than D32R (4.8%).Overall pregnancy per AI at 68 ± 3 d after AI did notdiffer (AIER = 35.5% vs. D32R = 34.7%). The hazardof pregnancy up to 210 d after first AI for all cowsenrolled (hazard ratio = 1.04, 95% CI 0.90 to 1.19)and for cows that received treatments only (D32R =308, AIER = 349; hazard ratio = 1.00, 95% CI 0.85 to1.19) did not differ. We conclude that a program aimedat increasing the proportion of cows reinseminated atdetected estrus by treatment with PGF_(2α) at 32 ± 3 dafter AI may be an alternative strategy for dairy farmsthat prefer or need to inseminate more cows at detectedestrus rather than by TAI.