Genetic Evaluation of Animals for Traits with Categorical Responses

A method of genetic evaluation of polychotomies based on the logistic distribution is presented. Logarithmic transformations of counts are expressed as linear combinations of fixed effects and random variables. Realized values of random elements in the model are predicted by the solution of equations similar to Henderson's multi-trait best linear unbiased prediction, but with a variance-covariance matrix of the residuals estimated from the data. It is proved that the method yields consistent estimators and predictors of response probabilities for any desired linear function of the model, provided that the linear combination involving the fixed effects is estimable. The method appears to have properties similar to those of minimum logit chi-square estimators. An example is presented.