Original Articles SummaryBackground: candidate genes and their polymorphisms have been associated with traits of economic interest in cattle, representing an important strategy for genetic improvement of complex traits. Bone morphogenetic protein 4 (BMP4) is a member of the transforming growth factor beta (TGFβ) superfamily, which is involved with several events of embryonic, fetal, and adult development in vertebrates. Objective: the aim of this study was to evaluate the degree of association between polymorphism in the BMP4 gene (guanine for thymine-G>T, SNP rs109778173) and the performance of Gyr oocyte donors, including the rate of cumulus-oophorus complex obtained in each session of follicular aspiration (OPU), embryo development, and pregnancy rates. Methods: DNA was extracted from hair follicles from 50 oocyte donors and genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Data from 212 OPU-IVP sessions was collected, and the following traits were associated with BMP4 polymorphism (SNP rs109778173): number and ratio of viable cumulus-oophorus complexes; number of cleaved embryos at day 4 of culture; number of transferable embryos at day 7 of culture, and pregnancies on days 30 and 60 after embryo transfer. Results: the studied BMP4 polymorphism was significantly associated (p<0.01) with the number and ratio of viable cumulus-oocyte complexes, and the ratio of pregnancies at 30 days. Conclusion: the GT genotype (SNP rs109778173) was associated with inferior performance regarding OPU-IVP traits. This finding suggests