Animal Science Department


Date of this Version

January 1980


Published in J Dairy Sci 1980, 63:1172-1180. Copyright © 1980 The American Dairy Science Association. Used by permission.


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 variancecovariance 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.