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Stayability Evaluation as a Categorical Trait and by Considering Other Traits

Department of Animal Science, Cornell University, Ithaca, NY 14853

ABSTRACT

Correspondence between usual categorical scores where frequencies sum to one and stayability of herd life measured as survival to several age periods is illustrated. The singularity of the variance-covariance matrix of categorically measured traits when each category is a separate trait also is true for stayability, since the measurement for the last period for stayability is always zero, has variance zero, and covariances zero with measurements in preceding periods. Best linear unbiased prediction for stayability of a bull's daughters is achieved by ignoring the last period. A procedure is described for predicting stayability of daughters having variable opportunity for stayability measurements that utilizes production and all available measures of stayability.