Partial lactations in genetic evaluation based on test day model

Abstract

The repeatability test day model was used to run genetic evaluation of bulls based on 305-day and partial lactation records (100, 150, 200 and 250 days). A total of 170 937 test day records of 18 974 Black-and-White heifers from the Wielkopolska region were analysed. The single-trait animal model included the fixed effects (herd-test-date, linear and quadratic regression on age at test day and four fixed regression coefficients describing lactation curves) and random effects (additive genetic and permanent environment and residuals). The standard error of prediction, correlations between true and predicted breeding values, and correlations between predicted breeding values from whole and partial lactations were used as criteria in the comparison of the obtained results. Evaluation based on 200-day and shorter partial lactations leads to a slight increase of prediction error variance and decrease in reliability when compared with 250-day and 305-day lactations. Very high correlations (+0.91-+0.98) between evaluations based on partial and 305-day lactations support the conclusion that partial records can be included in genetic evaluations.