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Genetic parameters for number of embryos produced by superovulated donors as heifers or cows using an in vivo or in vitro technique
Genetic gain in a population can be improved by using multiple ovulation and embryo transfer (MOET) in elite females. Multiple embryos can be produced using two different techniques, either using superovulation and producing the embryos in vivo or using ovum pickup (OPU) and in vitro production (IVP) of the embryos. Moreover, embryos can be produced by donor cows or virgin heifers as young as 7 months of age. The objectives of this study were to assess the genetic parameters for the number of embryos produced by Holstein donors superovulated either in vivo or in vitro and for the number of embryos produced by donors either as a cow or a heifer at embryo recovery. Data was provided by Holstein Canada and contained the number of viable embryos from every successful flushing performed across Canada. After editing, 137,446 records of superovulation performed on 54,463 donors between 1992 and 2014 provided information about the type of technique used, and 130,252 records from 51,323 donors provided information about the status of the donor (heifer or cow) at embryo recovery. Bivariate repeatability animal model analyses were performed. Heritability estimates for the donor were between 0.135 (0.007) and 0.155 (0.038), whereas estimates for the service sire were close to zero (from 0.004 ±0.002 to 0.019 ±0.010), indicating that the number of embryos produced is influenced by the genetic potential of the donor and not by the service sire. Moreover, moderate repeatability estimates indicated that the number of embryos produced should be somewhat consistent within a donor. Genetic correlations found for the number of embryos produced using either type of technique was strong (0.834 ±0.094) for the donor, but not significant for the service sire (-0.202 ±0.234). For the number of embryos produced by either a heifer or a cow, the genetic correlations were 0.702 (0.058) for the donor and 0.699 (0.206) for the service sire. Overall, our results suggest that the number of embryos produced by a superovulated donor should be similar regardless of the technique (in vivo or in vitro) used or the status (heifer or cow) of a donor at embryo recovery. On the other hand, using the same service sire will not increase similarity between the two techniques, but could influence the number of embryos produced by a donor as a heifer or as a cow in a similar way.
Keywords:
superovulation, Holstein, genetic parameter