METHOD AND EFFECT OF ADJUSTMENT FOR HETEROGENEOUS VARIANCE OF HOLSTEIN CONFORMATION TRAITS

Type classification records of Canadian Holsteins were investigated fo r evidence of heterogeneous variance across herds. Data consisted of r ecords for 1,139,104 cows from 20,226 herds with classifications on 26 conformation traits collected from 1982 through 1992 and 338,046 cows from 9600 herds with classifications on 2 additional traits from 1990 through 1992. Phenotypic standard deviations of herd-round-classifier were fitted to a mixed model that included round, classifier, and reg ion as fixed effects, herd size as a covariant, and herd as a random e ffect. Estimates of the variance components, solutions of fixed effect s, and BLUP estimates for herd were obtained by maximum likelihood pro cedures. Repeatability of within-herd standard deviation across rounds ranged from 1.4 to 10.3% for the 28 traits. Type classification data were subsequently standardized for phenotypic standard deviations of h erd-round-classifier that were derived from estimates of the fixed eff ects and the BLUP estimate of the herd effect. Genetic evaluations for cows and bulls were produced from adjusted and unadjusted data. Corre lations between 3754 sire and 1,142,782 cow estimated transmitting abi lities obtained from unadjusted and adjusted data were essentially uni ty. Although some evidence of heterogeneous variance existed across he rds for 28 conformation traits, standardization of the classification records had only a minor effect on genetic evaluations.