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Joint Sire and Cow Evaluation for Conformation Traits Using an Individual Animal Model

Centre for Genetic Improvement of Livestock, Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1

ABSTRACT

A joint sire and cow evaluation for selected type traits has been carried out for the Canadian Holstein population using an individual animal model accounting for all known relationships. Only first lactation, first classification linear records were utilized. Linear scores for final class/final score (combined), feet and legs, mammary system, and stature were analyzed. The model of analysis included animals' additive genetic merit as random and herd-round-classifier subclasses as fixed effects. Calving age and stage of lactation at classification were fitted as linear and quadratic covariables. There were 282,030 cows with records, 198,871 dams without records, and 8481 sires (i.e., 489,382 animals in total). Combined with 33,968 herd-round-classifier effects in 9654 herds and four regression coefficients, a system of 523,354 equations required simultaneous solution. Solutions were obtained iteratively for one trait at a time. The computing strategy utilized is described, and a detailed worked example is given. Correlations between sire proofs and the current Holstein sire proofs were .89 to .96 for sires with at least 20 daughters in five or more herds. Correlations between cow indexes and phenotypic scores ranged from .53 to .76. The coefficient of determination in a multiple regression of daughter's index on dam's index and sire's and maternal grandsire's proof was 78 to 92% but only 59 to 83% when dam's index was replaced by dam's phenotypic record.

¹ Institute of Animal Genetics, Edinburgh University, West Mains Road, Edinburgh EH9 3JN, Scotland.