The aim of this study was to evaluate the efficacy of the synchronization of ovulation for fixed-time embryo transfer in crossbred recipient heifers (Bos taurus indicus x Bos taurus taurus). At Experiment 1, ovarian ultrasonography was performed to evaluate follicular dynamics during the "Ovsynch" protocol (G1; n=35) or single PGF2alpha injection (G2; n=34). At Experiment 2, the same treatments were used at field conditions in 168 (G1) and 177 (G2) heifers. On D6, ovarian ultrasonography and blood collection for P4 assay were performed. On D7, a embryo was transferred. At Experiment 1, 45.7% of the heifers ovulated after the 1st and 74.3% after the 2nd GnRH injection (P<0.05). The ovulation rate in G2 was 58.8%. In G2, 64.7% of the heifers were detected in estrus and in Gl, 22.9% (P<0.01). At Experiment 2, Gl had more selected heifers for embryo transfer than G2 (72.6% vs. 45.2%; P<0.01). Conception rates were 49.2% and 56.3% in G1 and G2, respectively (P>0.05). Thus, the pregnancy rate in Gl was 35.7% and 25.4% in G2 (P<0.05). Estrus was detected in 53.7% of the recipients in G2 and 33.3% in those of the Gl (P<0.05). It was verified that CL with larger area induced an increase on P4 concentration and on the conception rate of both groups (P<0.05). The synchronization of ovulation for fixed-time embryo transfer increased the ovulation, the selection and the pregnancy rates in recipient heifers.
Progesterone; Pregnancy rate; Embryo recipient; Bovine; Corpus Luteum
