Genetic and genomic analysis of superovulatory response in Canadian Holsteins

Abstract

Superovulation of dairy cattle is frequently used in Canada. The cost of this protocol is high, and so is the variability of the outcome. Knowing the superovulatory potential of a donor cow could influence the breeder’s decision to superovulate it or not. The main objective of this study was to perform a genetic and genomic analysis for superovulatory response of Holstein cows in Canada, using data recorded by Holstein Canada. Data contained the total number of embryos and the number of viable embryos from every successful flushing performed across Canada. After editing, 137,446 records of superovulation done between 1992 and 2014 were considered for the analysis. A univariate repeatability animal model analysis was performed for both total number of embryos and number of viable embryos. As both data and residuals for total number of embryos and number of viable embryos did not follow a normal distribution, records were transformed using either logarithm transformation or Anscombe transformation. Using log transformation heritability estimates (SE) of 0.15 (0.01) and 0.14 (0.01) were found for total number of embryos and number of viable embryos, respectively. Using Anscombe transformation the heritability estimates (SE) were 0.17 (0.01) and 0.14 (0.01) for total number of embryos and number of viable embryos, respectively. Estimated breeding values of sires with reliabilities higher than 40% were used for calculating correlations between estimated breeding values and other routinely evaluated traits. The results showed that selection for a higher response to superovulation would lead to a slight decrease in production, but an improvement for functional traits, including all reproduction traits, however in all cases the estimated correlations are either low or modest. Considering the results obtained in this study, genetic selection for increased superovulatory response in donors is possible.  Preliminary results from a genome-wide association study showed that one big region on chromosome 11 seems to be associated with superovulatory response, but more research is needed to confirm this finding.