Estimating variances and covariances for multivariate animal models by restricted maximum likelihood

Abstract

Restricted maximum likelihood estimates of variance and covariance components can be obtained by direct maximization of the associated likelihood using standard, derivative-free optimization procedures. In general, this requires a multi-dimensional search and numerous evaluations of the (log) likelihood function. Use of this approach for analyses under an animal model has been described for the univariate case. This model includes animals' additive genetic merit as random effect and accounts for all relationships between animals. In addition, other random factors such as common environmental or maternal genetic effects can be fitted. This paper describes the extension to multivariate analyses, allowing for missing records. A numerical example is given and simplifications for specific models are discussed.