Genetic parameters affecting 180-days standardised milk yield, test-day milk yield and lactation length in Spanish Assaf (Assaf.E) dairy sheep

A total of 42,197 records of test-day milk yield (TDY) and 7654 lactations from 3854 individuals belonging to the Spanish Assaf (Assaf.E) breed were analysed using univariate and multivariate models to estimate genetic parameters affecting TDY, total milk yield standardised to 180 days (MY180) and lactation length (LL) in order to asses their possibilities of use in the selection scheme of the Assaf.E population. Estimates of h2 were, in general, on the lower limit of those usually reported for the three analysed traits. Estimates of heritability for MY180 varied from 0.131 to 0.177. Estimates of h2 for LL and TDY were consistent regardless the estimation model being of, roughly, 5% and 10%, respectively. The estimates for the permanent environmental effect (c2) of TDY were consistently the same (0.27–0.28) regardless the fitted model whilst they showed large differences for LL and MY180. Genetic correlations were always positive and high ranging from 0.792 for the pair LL-TDY to 0.999 for the pair MY180-TDY. Correlations between permanent environmental effects were even higher ranging from 0.932 for the pair LL-MY180 and 0.999 for the pair MY180-TDY. The advantages of using TDY as selection criterion in the Assaf.E improvement scheme are discussed.