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FACTORS THAT AFFECT THE RESUMPTION OF THE POSTPARTUM OVARIAN ACTIVITY AND PREGNANCY RATE IN DUAL-PURPOSE COWS IN SOUTHEAST OF MEXICO

Background. The resumption of ovarian activity after parturition is related to reproductive efficiency. Objective. To determine the effect of breed group and some non-genetic factor on resumption of ovarian activity and pregnancy rate of dual-purpose cows. Methodology. In study 1, 37 cows were sampled biweekly, from the day 15 to 150 postpartum or until a corpus luteum (CL) was detected. Follicular population (FP), maximum follicle diameter (MFD) and maximum CL diameter (MCLD) were also measured. In study 2, 71 cows were pregnancy diagnosed. Chi2 tests and analyses of variance were performed to determine the effects of breed group, parity number, body condition score (BCS), BCS change (BCSC) and body weight change (BWC) on the dependent variables. Results. In study 1, aproximately, 84% of cows resumed ovarian activity at 68.3 days. More CL were found in multiparous cows (92.59%) and those with BCS ≥3.0 (95.83%). No differences were found in the FP and MFD. F1 cows had the largest MCLD (19.51 mm). In study 2, pregnancy rate was higher in cows with 2-3 (47.83%) and ≥4 parities (54.55%), F1 (54.29%) cows, those gaining BCS (64.29%) and high body weight (66.67%). Implications. Results suggest that primiparous cows and those with BCS ≤2.5 require better management; therefore, strategies must be established to improve reproductive efficiency. Conclusion. Primiparous and cows with BCS ≤2.5 delayed the first ovulation. Multiparous, F1 cows, those gaining BCS and body weight after calving had the highest pregnancy rate. 