DISCUSSION
Population means and heritability estimates for the
performance-tested animals have been discussed in detail by Crowley et al. (2010). Mean survival to subsequent lactation may be artificially inflated in the present study because data from recent years predominate
where the incidence of sire recording increased, and
because of the editing criteria imposed, animals culled,
but not recorded, that have not calved more than 800
d from the last calving or the date of data extraction