Factor analysis for evaluating relationships between herd life and type traits in Swiss Brown cattle

Abstract

The genetic and phenotypic correlation matrices of 18 type traits scored during the first lactation on 9224 daughters of 274 Swiss Brown test sires were used to derive uncorrelated genetic and phenotypic factors for evaluating relationships of two herd life measures with type traits. A principal component analysis was applied to the correlation matrices to choose genetic and phenotypic components which mostly account for the total variation in type traits. Five genetic and five phenotypic components, explaining 74% of the total genetic and 58% of the total phenotypic variation in type traits respectively, were retained for the subsequent analysis. New genetic and phenotypic factors were defined by principal factor analysis. The new factors were then rotated in order to determine contribution of the individual traits to the particular factors. Factor pattern coefficients were used to compute genetic and phenotypic factor scores from the original type traits. Sire PTA for genetic factor scores, and cow phenotypic factor scores were used as explanatory variables in a multiple regression analysis to model the relation between herd life and the factors. Both herd life measures considered — true and functional herd life — were influenced by genetic and phenotypic factors which include udder and teat traits, typical dairy body characteristics, and certain feet and leg traits. Sire PTA for genetic factors explained about 13 of total genetic variance in herd life. Both genetic and phenotypic factors for type traits explained only a small part of the variance in herd life. The revision of the type classification system is recommended.