Sex ratio of in vitro produced embryos 60 days after fixed-time embryo transfer according to the developmental stage of the implanted embryo

Abstract

In view of its wide and consolidated sale of bovine embryos and because it has the world’s largest herd, Brazil currently occupies an important position in the worldwide scenario of in vitro production (IVP) of embryos. However, sex ratio deviations have been frequently reported for IVP embryos. The objective of this study was to evaluate the pregnancy rates and fetal sex of IVP bovine embryos 60 days after fixed-time embryo transfer (FTET). Nellore females (Bos taurus indicus, n=2,920) were used as oocyte donors and 30,912 crossbred cows (Bos taurus indicus x Bos taurus taurus) were used as recipients. Of these recipients, 11,341 were submitted to fetal sexing at 60 days of gestation. No difference (P>0.05) in pregnancy rate or embryo loss was observed between stages of embryo development at the time of FTET (early blastocyst, blastocyst, and expanded blastocyst). Regarding the sex of the products obtained, there was a higher percentage of male embryos in the blastocyst and expanded blastocyst stages and a higher percentage of female embryos in the early blastocyst stage. It should be noted that the results obtained for embryos in the blastocyst and expanded blastocyst stages are highly reliable, considering that a significant number of embryos in these stages were transferred. The results obtained for embryos in the early blastocyst stage should be seen with caution in view of the reduced number of embryos in this stage.

Keywords

• embriões bovinos
• prenhez
• produção in vitro
• sexagem fetal