Genomic breeding value for number of OPU derived oocytes in bovine

The success of embryo production by ovum pick-up (OPU) in vitro production (IVP), is determined to a large extent by the initial number of oocytes that can be collected per donor cow. This number of oocytes varies per cow and has a heritability of 0.3 (Merton et al 2009, Theriogenology. 72:885-893). A genomic (based on DNA markers) breeding value for the number of oocytes could be used to select female animals (at young age) that give a high number of oocytes. Since OPU-IVP within CRV is already carried out for more than 20 years and almost all animals are genotyped, the development of such genomic breeding values for OPU should be possible and more accurate than a pedigree-based breeding value. The aim of this study is to determine the reliability of genomic breeding values for OPU. The total dataset contained 2,543 female Holstein Friesian animals with in total 40,734 OPU sessions. From these animals, 890 were genotyped with the Illumina 50K SNP chip (reference population). Classical (pedigree based) and genomic (pedigree + DNA marker based) breeding values were estimated using the singe-step BLUP method. Reliability was determined as the correlation between the pedigree-based or genomic breeding value before OPU records were obtained with the realized number of oocytes after OPU using cross-validation. Based on this dataset the reliability was 0.21 for the pedigree-based breeding values and the reliability increased to 0.29 when genomic information was added. The reliability of genomic breeding values for OPU oocytes was significantly lower than reliabilities obtained for milk production traits (which are around 0.65), but in that case the reference population is much larger, i.e. ~40,000 animals. When selecting the best or the worst 10% based on the genomic breeding value for oocytes, the best animals give two times more oocytes than the worst, 5.0 and 10.8 oocytes respectively. This shows that there is substantial genetic variation in OPU oocytes. This study shows that it is feasible to estimate genomic breeding values for the number of oocytes derived after OPU before OPU records are obtained (no phenotypic data yet). This breeding value has a reliability that is high enough to be of practical use. The breeding value can be used to select donor female animals for optimal use in an OPU-IVP embryo production program. Since all animals in the CRV OPU program are genotyped, the reference population will grow over the coming years resulting in more reliable genomic breeding values.