Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 1999
Publication Date: N/A
Interpretive Summary: Recent advances in computation of genetic evaluations for conformation (type) of dairy cattle have included multitrait analysis and the use of animal models. The objective of this study was to use those advances to evaluate more accurately the genetic merit of U.S. dairy cattle for type traits. Data included final scores and scores for 15 linear type traits (stature, strength, dairy form, foot angle, rear legs side view, body depth, rump angle, thurl width, fore udder attachment, rear udder height, rear udder width, udder depth, udder cleft, front teat placement, and teat length). Genetic parameters needed to calculate evaluations were estimated, and a method to adjust data for the effects of age at appraisal was developed. The statistical model for evaluations included the effects of an animal's genetic merit, its permanent environment, and the interactions of herd and sire; herd, appraisal date, and parity; parity and appraisal age; and parity and lactation stage. A single-trait animal model was applied for final score, and a multitrait animal model was used for linear type traits. The system developed in this study was implemented in the United States in February 1998 for the genetic evaluation of type traits of Ayrshires, Brown Swiss, Guernseys, Jerseys, Milking Shorthorns, and Red and Whites. The improved evaluations will provide more accurate information on which breeders can base selection decisions for type traits of economic importance to them.
Technical Abstract: A system to calculate genetic evaluations based on an animal model was developed for final score (single-trait model) and 15 linear type traits (multitrait model) of Ayrshires, Brown Swiss, Guernseys, Jerseys, and Milking Shorthorns. (Co)variance components were estimated from appraisals that were scored during 1988 and later and that included all linear traits. The model for (co)variance components included fixed effects for interactions of herd, appraisal date, and parity; parity and appraisal age; and parity and lactation stage. Random effects were included for permanent environment, animal, and residual. A canonical transformation was used with approximate diagonalization. Data for estimating breeding values included appraisals from 1980. Effects for appraisal age and lactation stage were defined within appraisal year group. The model for calculation of breeding values also included a random effect of interaction between herd and sire. Solutions for appraisal age from a preliminary analysis were smoothed with a quadratic curve to generate additive age adjustments by month for appraisal age, parity, and appraisal year group. Correlations of animal model and sire model solutions for bulls that were born during 1975 or later and had 20 daughters or more were highest (generally 0.90 or higher) for Guernseys and lowest (generally less than 0.80) for Milking Shorthorns. The evaluation system was implemented in February 1998 and was extended to Red and Whites.