Abstract

FLORES DOMINGUEZ, Silvano et al. Pregnancy in dairy cows with two protocols for synchronization of ovulation and timed artificial insemination. Rev. mex. de cienc. pecuarias [online]. 2015, vol.6, n.4, pp.393-404. ISSN 2448-6698.

The objective was to compare the pregnancy rate (PR) between two timed AI protocols in dairy cattle. Two hundred seventy-five (275) cows were presynchronized with PGF2α given 14 d apart beginning at d 32 postpartum; 12 d after second PGF2α, cows were assigned to two treatments: 1) Ovsynch (n=144) received GnRH, followed 7 d later by PGF2α and then GnRH 56 h after PGF2α and cows were inseminated 16 h later 2) PRID5d (n=131), received GnRH and a progesterone-releasing intravaginal device, which remained in place 5 d. Cows received an injection of PGF2α at the time of progesterone device removal and a second injection of PGF2α 24 h later. At 56 h following progesterone device removal, the next injection of GnRH was given and cows were inseminated 16 h later. Pregnancy diagnosis was performed 45 d after AI by transrectal palpation. PR was compared by logistic regression analysis. Independent variables were: treatment (Ovsynch vs PRID5d), milk yield (≤40 vs >40 kg), technician (1 vs 2), puerperium (normal vs abnormal), parity (primiparous vs multiparous) and standing estrus during presynchronization. PR was similar (P>0.1) between treatments (27 vs 21 %; Ovsynch and PRID5d, respectively). There was no effect of the other independent variables on PR. The interaction of these variables with the treatment did not affect PR (P>0.1). In conclusion, PR was similar in dairy cows inseminated by an Ovsynch protocol or through modified Ovsynch which included progesterone during 5 d and reduction of the interval between the GnRH and PGF2α from 7 to 5 d.

Keywords : Ovsynch; Progesterone; Fertility; Dairy cows.