Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 9, 1997
Publication Date: N/A
Interpretive Summary: All dairy breed associations and many artificial-insemination organizations in the United States have implemented linear type (conformation) trait programs. The American Jersey Cattle Association (AJCA) currently scores 15 type traits and assigns a final score. Genetic evaluations for linear type traits and for final score of Jerseys currently use a single-trait sire model, but use of a multitrait animal model would improve accuracy of evaluations. In this study, a multitrait animal model was used to predict genetic merit and the accuracy of the prediction for final score and 15 linear type traits of U.S. Jersey cows. Inbreeding was considered in the computations. Genetic trend was strongly positive for dairy form, final score, and rear udder traits (height and width) and negative for udder depth. For other traits, genetic trend was small. The evaluation methodology developed will improve accuracy of genetic evaluations for type traits of U.S. Jerseys and will allow dairy cattle breeders to make greater genetic progress for conformation traits.
A multitrait animal model was used to calculate predicted transmitting abilities (PTA's) and reliabilities for final score and 15 linear type traits of 225,632 U.S. Jersey cows. Records were adjusted for age and stage of lactation before analysis. The model contained effects for interactions of herd and date scored; year scored, parity, and age; and herd and sire as well as effects of permanent environment and additive genetics. Of the 381,511 records included, some observations were missing for final score (8%), body depth (43%), and teat length (33%). Solutions were obtained with canonical transformation adapted to include several random effects and estimation of missing values with each iteration. Inbreeding was considered in the computations. Convergence was achieved in approximately 50 rounds of iteration. Correlations between animal and sire model PTA's ranged from 0.56 to 0.95 and generally were higher for bulls than for cows and for more recent birth years. Genetic trend was strongly positive for dairy form, final score, and rear udder traits (height and width) and negative for udder depth. For other traits, genetic trend was small. This methodology should improve accuracy of genetic evaluations for type traits of U.S. Jerseys.