Fatores que influenciam no sucesso da produção in vitro de embriões em receptoras bovinas criadas na região da Amazônia legal

Abstract

The aim of the present study was to evaluate transfer efficiency in bovine embryos in vitro produced (IVP) in the Legally-defined Brazilian Amazon. In order to do so, two experiments were conducted. In Experiment I, embryos at different stages of development were inovulated in cows with different corpus luteum types, either in dry or rainy season. 5403 embryos transfers were evaluated, with IVP embryos at different stages of development. The oocytes were obtained from zebu females through vaginal aspiration guided by sonogram, matured, fertilized, and cultured in vitro. The embryos were inovulated in the stages of morula (MO), early blastocyst (BI), blastocyst (BL), expanded blastocyst (BX), blastocyst hatching (BN) and hatched blastocyst (EB) in cyclic crossbred cows. Corpus lutea were classified by ultrasonography in protruded (CL1:> 200mm, CL2: 160 to 200mm, CL3: 100 to 159mm) and included (CL <150 mm). 34.30% (1855) of the animals conceived, with significantly higher pregnancy rate of stage BX embryos (38.2%). The result of BX only did not differ significantly from that obtained in females inovuladas with embryos stage BN (35.9%) and BN did not differ MO, BI and BL (P>0.05). The analyses showed no correlation between corpus luteum size or type and the development of IVP embryos inovulated at different stages. Pregnancy rates did not differ for inovulations performed in dry and rain season, with 33.7% and 35.7% mean respectively (P>0.05). Experiment II aimed to evaluate optimal time for inovulation of bovine females with IVP embryos after seven days, as a function of estrus manifestation, either in dry or rainy season. Among 2234 inovulated receptors, Estrus manifestation was observed two days before (D-2) in 31 of the recipients, one day before (D-1) in 473, on the exact day (D-0) in 1.247, one day after (D+1) in vitro fertilization, in 472, respectively, and 11 of the animals revealed estrus behavior two days (D+2) after in vitro fertilization. 35.27% of all inoculated animals conceived. The pregnancy rate for D0 was 57.90%, , while for D-2, D-1, D+1 and D+2, such percentages were 0.37%, 22.34%, 19.02 and 0.37%, respectively. Considering pregnancy rates, no significant difference (P>0.05) was observed between D-1, D-0 and D+1, which also displayed no significant difference for synchronization to D-1, D-0 and D+1 in either seasons (P>0.05). The results obtained after embryo transfer with IVP from Amazon Region were similar to studies in other regions and not influenced by the season. These results show the need for continuous research in order to address oocyte development problems for the production of quality embryos, augmenting the knowledge in the area and optimizing the use of IVP, which will ultimately enable the dissemination of this technology, and increase livestock production efficiency. Therefore, it can be concluded that a synchronism of ± 1 day interval from estrus manifestation is optimal for the achievement of pregnancy through in vitro fertilization, and that in the Legally-defined Brazilian Amazon, the season is not a limiting factor for the maintenance of successful pregnancies.