Oocytes recovery by follicular aspiration and analysis of in vitro embryo production in Gir and Nelore breeds (Bos indicus)

Abstract

We aimed to analyze, through a retrospective study, the relationship between the number of oocytes, number of embryos, embryo rate from follicular aspiration sessions (OPU), and in vitro embryo production (IVEP) from donor cows of the Gir and Nelore breeds. Data from 4,238 OPU/PIVE sessions performed on donors of the Gir (n = 1,115) and Nelore (n = 3,123) breeds, between 2008 and 2010, were analyzed. The variables analyzed were the number of viable oocytes, number of embryos, rate of embryos and the percentage of OPU/IVEP sessions that did not produce embryos in PIVE. Such variables were divided into quartiles by the number of oocytes. ANOVA was used to compare means between breeds and quartiles, with Levene's test of homogeneity of variance, followed by the Bonferroni test. The chi-square test was used to compare the percentage of OPU sessions that did not produce embryos in PIVE. In all analyzes a significance level of 5% was considered. In the comparison between breeds, the Nelore breed presented a higher average (p < 0.001) for number of oocytes, number of embryos and embryo rate, and a lower percentage (p < 0.001) of OPU/IVEP sessions that did not produce embryos compared to the Gir breed. In the analysis by quartiles, there was an increase (p < 0.05) in the average number of oocytes and embryos from the lower quartile to the upper quartile, within each breed. When comparing quartiles between breeds, the Nelore breed presented higher values (p < 0.05) in the number of oocytes, embryos and embryo rate in all quartiles. The percentage of OPU/IVEP sessions that did not produce embryos reduced significantly (p < 0.05) as the number of oocytes increased in the quartiles. In conclusion, the Nelore breed presented higher averages of oocytes, embryos and embryo rate compared to the Gir breed. The number and percentage of sessions that did not produce em-bryos were lower in the Nelore breed. The greater number of oocytes reflected an increase in the number of embryos, and a reduction in the number and percentage of OPU sessions that did not produce embryos.