Eficiencia reproductiva de Ovsynch + CIDR en vacas Holstein bajo un esquema de inseminación artificial a tiempo fijo en el norte de México

The use of Ovsynch plus controlled internal drug release of progesterone (CIDR) in high producing dairy cows was evaluated. The study was carried-out at the Comarca Lagunera (25° 44´ N, 103° 10´ W, at 1,111 m asl.) during December and January. Cows (n= 100) were pre-synchronized with two injections of PGF2α at 35 and 47 d postpartum and assigned to two treatments (n= 50 each). 1) The group OV received the Ovsynch protocol: 100 μg GnRH (i.m.; d 1), 25 mg of PGF2α (i.m.; d 7), and 100 μg GnRH (i.m.; d 9); 2) The group OV+C was subjected to the Ovsynch protocol plus a CIDR (1.38 g P4) which was removed at d 7. Cows of both groups were exposed to a fixed time artificial insemination protocol (IATF; 16 to 20 h after the last injection). Response variables included pregnancy rate, cows with repeated estrus considering two periods, ≤24 and ≥25 d after insemination, and the period to return to estrus. While no differences occurred between groups regarding pregnancy rates (OV= 28 %, OV+C= 32 %; P >0.05), the percentage of cows showing estrus after IATF differed ( P <0.05) between treatments for the two studied periods (28 % vs 62 % ≤24 d; 69 % vs 35 % ≥25 d; OV and OV+C, respectively). Moreover, mean of days when cows repeated estrus was lower ( P <0.05) in the OV+C group (25 ± 1.6 vs 30 ± 1.3 d). Although the Ovsynch+CIDR treatment did not improve pregnancy rate, it reduced the latency for return to estrus, emerging as an alternative to diminish the days to the next AI, and potentially improve the reproductive efficiency and the economic return of the dairy herd.