Genetic parameters for oocyte number and embryo production within a bovine ovum pick-up–in vitro production embryo-production program

Abstract

Genetic factors influencing the outcome of bovine ovum pick-up–in vitro production (OPU-IVP) and its relation to female fertility were investigated. For the first time, genetic parameters were estimated for the number of cumulus-oocyte complexes (Ncoc), quality of cumulus-oocyte complexes (Qcoc), number and proportion of cleaved embryos at Day 4 (Ncleav D4, Pcleav D4), and number and proportion of total and transferable embryos at Day 7 of culture (Nemb D7, Pemb D7 and NTemb D7, PTemb D7, respectively). Data were recorded by CRV (formally Holland Genetics) from the OPU-IVP program from January 1995 to March 2006. Data were collected from 1508 Holstein female donors, both cows and pregnant virgin heifers, with a total of 18,702 OPU sessions. Data were analyzed with repeated-measure sire models with permanent environment effect using ASREML (Holstein Friesian). Estimates of heritability were 0.25 for Ncoc, 0.09 for Qcoc, 0.19 for Ncleav D4, 0.21 for Nemb D7, 0.16 for NTemb D7, 0.07 for Pcleav D4, 0.12 for Pemb D7, and 0.10 for PTemb D7. Genetic correlation between Ncoc and Qcoc was close to zero, whereas genetic correlations between Ncoc and the number of embryos were positive and moderate to high for Nemb D7 (0.47), NTemb D7 (0.52), and Ncleav D4 (0.85). Genetic correlations between Ncoc and percentages of embryos (Pcleav D4, Pemb D7, and PTemb D7) were all close to zero. Phenotypic correlations were in line with genetic correlations. Genetic and phenotypic correlations between Qcoc and all other traits were not significant except for the phenotypic correlations between Qcoc and number of embryos, which were negative and low to moderate for Nemb D7 (–0.20), NTemb D7 (–0.24), and Ncleav D4 (–0.43). Results suggest that cumulus-oocyte complex (COC) quality, based on cumulus investment, is independent from the total number of COCs collected via OPU and that in general, a higher number of COCs will lead to a higher number of embryos produced. The correlation between the estimated breeding values for Ncoc and PTemb D7 of sires in this study and the sires breeding index for female-fertility based on the Dutch cattle population was close to zero. This study revealed OPU-IVP traits (Nemb D7, NTemb D7, and Ncoc) that could be of potential value for selection. Introduction of such traits in breeding programs would enhance the number of offspring from superior donors as well as improve the cost efficiency of OPU-IVP programs.