Additive and Nonadditive Genetic Variation for Conformation Traits in Canadian Holsteins

¹ Centre for the Genetic Improvement of Livestock, Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1

Additive and dominance genetic variances for nine conformation traits in the Canadian Holstein population were estimated by REML using the derivative-free algorithm. All traits were analyzed under two sire and dam models differing in assumptions on the data structure. Within-herd relationships due to dam were defined first to be nested within sire in order to estimate both genetic variances, assuming unimportant biases on the estimates. The potential impact of some of these biases was estimated as the difference between the two parental variance components under a cross-classified model. Heritabilities were similar to those previously computed for Canadian Holsteins and ranged from .10 to .30. Results from the hierarchical dam-within-sire model suggest dominance genetic variation, as a proportion of the total variation, to be important for final score (.15), capacity (.16), and mammary system (.13). However, estimates of dam components, as a proportion of the total variance, were significantly greater than sire components for final score (.019), general appearance (.020), and feet and legs (.018) under the cross-classified model. Therefore, the significant dominance genetic parameter estimated for final score under the hierarchical model may have been biased upward.

Key Words: heritability • dominance genetic variation • conformation

Submitted on August 31, 1989
Accepted on January 26, 1990