Factors affecting embryo production in superovulated Nelore cattle 1

Abstract Understanding the factors involved in embryo production in superovulated cows is fundamentally important in order to plan a program of embryo transfer. The present study analyzed the relevance of both intrinsic and extrinsic factors related to embryo production in Nelore cows (Bos taurus indicus). We studied 884 superovulation inductions in 318 donor cows ranging from 2 to 21 years of age, on six farms located in the state of Mato Grosso do Sul, Brazil. The data were analyzed using a General Linear Model in the SAS software package. The number and quality of the recovered embryos were not affected (P > 0.05) by continuous superovulation treatment (i.e., inducing superovulation up to six times), by the source of the hormones used (Pluset , by the hormone dosage (50, 75 or 100%), or by synchronization of follicular wave emergence with progestogens. Donor age negatively affected the number and quality of the embryos. Senile (>14 years) cows produced, on average, 5.0 ± 0.2 fewer total embryos and 3.0 ± 0.1 fewer transferable embryos than young cows (P < 0.001). The farm management increased the number of transferable embryos by 2.0 ± 0.4. We conclude that farm management and donor age are the main factors that should be considered when implementing a program of embryo transfer in Nelore cows submitted to superovulation treatment