Factors that affect the pregnancy rate with zebu embryos in vitro produced in the tropic

Objective. To study the factors affecting the success of embryo transfers (ET). Methodology. 1087 ET from zebu cattle were analyzed. The considered extrinsic factors of the donor cows (DC) were the cattle production unit (CPU) from which they were sourced (n=13), amount of transfers in the unit (1 time, >1 time), geographical zone (n=4), period (dry or rainy) , year season (winter, spring, summer or fall); and the intrinsic factors were DC and bull breed, semen (conventional or sexed), embryo quality (EQ) and embryo developmental stage (EDS) The factors considered in the recipient cows (RC) were corpus luteum size (CL1, CL2 or CL3), period (dry or rainy) and year season (winter, spring, summer or fall). Statistics were compiled with ci2 2 for the analysis of the main effects , correlations were estimated through a multivariate clustering analysis. Results. The general pregnancy rate (PR) was 37.99 +/- 1.47, and there were differences (p<0.05) observed among the CPU (2.78-75%). The PR was higher in the dry than in the rainy period (44.55 vs 31.28%), and in fall and winter (p<0.05) than spring and summer (42.76, 43.98, 37.57 and 29.77%, respectively), and there were differences observed between the geographical zones as well (p<0.05). The PR was higher with excellent-quality embryos (p<0.05) than with good-quality embryos (38.9 vs. 26.3%). The period and year season had an effect over the RC (p<0.05), and the grouping analysis showed a correlation (r>0.90) between the period and year season during Oocyte pick-up (OPU) over the PR; moreover, semen, EQ and EDS had larger associations with the PR (r>0.80). Conclusions. Environmental conditions at the moment of OPU and EQ are factors worth considering in embryo transfer programs with zebu cattle using in vitro produced embryos in tropical conditions.