Contribution of stayability records to the accuracy of selection for improved production value and herd life

Abstract Stochastic simulation was used to determine the potential of cow survival rate, or stayability, as a supplement to production for use in a genetic index when the sires of young AI bulls are selected to improve economic returns. Production alone, production with stayability to 48 mo, production with 48- and 60-mo stayabilities, and production with herd life were used in genetic indexes to improve the aggregate genotype. Aggregate genotype was defined as the weighted sum of the genetic values of first lactation production and of the fifth lactation involuntary culling record. Cow lifetime histories for production were simulated by independent application of yearly culling criteria on low production and unsatisfactory secondary traits. Parameters for selection indexes were estimated from replications of 150 sire families with 200 half-sib progeny each. An index using production and stayability records was relatively more accurate than an index using production alone. Accuracy of selection can be increased 2 to 4% using 48- and 60-mo stayabilities. A stayability record from an early herd-life period and a second stayability record from a later period could be used to supplement production traits for economic evaluation of sires. In principle, the use of a pair of stayabilities enables the indirect measurement of rates of some involuntary culling from a later period, whereas the rates of some culling for low production for a stayability record from an earlier period are held constant.