Abstract
The objective of this study was to evaluate the effectiveness of synchronization of follicular wave emergence using steroid hormone treatments in Nelore cows. Donors were placed into three groups. Those that were between days 9 and 12 of their cycle (estrus=day 0) formed the TI group (n=60), whilst those that were in any other stages of their estrus cycle constituted groups TII (n=60) and TIII (n=60). TI donors were submitted to a standard protocol of superovulation, however, TII and TIII donors were treated with the Syncro-Mate-B (SMB) or Controlled Internal Drug Releasing Device (CIDR-B) programs, respectively. Superovulation was induced with p-FSH, divided into eight decreasing doses at intervals of 12 h. The donors received cloprostenol 48 h after the beginning of the treatment and progestagens were removed 12 h later. Artificial inseminations (AI) were done at 12 and 22 h after the initiation of estrus and the embryo collections were done 7 days after AI. In the donors which displayed behavioral estrus, mean (±S.E.M.) total ova and viable (transferable) embryos were 15.8±1.4 and 8.3±1.0 (TI, n=56); 15.6±1.3 and 8.9±1.0 (TII, n=56); 17.3±1.0 and 9.9±0.9 (TIII, n=57), respectively, with no significant difference (P≥0.05) among groups. In those animals that did not displayed behavioral estrus, the mean values of total ova and viable embryos were 3.5±1.6 and 0.7±0.5 (TI, n=4); 11.5±3.9 and 9.0±4.4 (TII, n=4); 8.7±5.0 and 5.0±2.9 (TIII, n=3), respectively, with no significant differences (P≥0.05) among groups. Pregnancy rates of 62.2% (TI, n=235); 66.4% (TII, n=284) and 65.1% (TIII, n=244) were obtained with embryos transferred from these collections and did not differ significantly (P≥0.05) among groups. It was concluded that the synchronization of the emergence of follicular waves in Nelore donors is usable and does not harm the efficiency of embryo transfer programs. In addition, in contrast to the standard superovulation protocol, this method permits the use of a large number of donors in a short time period, at any stage of the estrus cycle, minimizing the costs of embryo transfer.
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