The Usefulness of Selection for Yield and Functional Type Traits

Abstract

Udder depth, teat placement, foot angle, and milk yield measured in first lactation were evaluated in an index to improve a breeding goal consisting of milk yield and involuntary culling. Efficiencies of response for full and reduced indices were calculated for various economic values and genetic parameters from the literature. Sire and individual (based only on cow's performance) indices were calculated. Selection only for milk would result in 87 to 97% of the expected progress in the breeding goal when all four traits were included. Standardized b-values (index coefficients) for milk were about two to three times the sum of the standardized b-values for the type traits. Predicted response in the aggregate genotype was sensitive to genetic correlations between involuntary culling and type traits. Predicted response was insensitive to small changes in heritability for involuntary culling or changes in genetic correlations between milk and type traits. Selection on udder traits, foot angle, and production would result in only a small increase in efficiency above selection on production alone. However, these type traits may help reduce involuntary culling or limit correlated increases in involuntary culling associated with increased milk yield.