Environmental Correlation Between Paternal Half-Sisters for Milk and Milk Fat Production

Abstract

Environmental correlations (c2) among paternal half-sisters in the same herd were estimated by four different methods. The data were 55,170 first lactation records in 2,326 herds in eight midwestern states. Both mature-equivalent and deviation records of milk and milk fat were used. The intraclass correlation within herds and sires estimates an environmental correlation due to the variation within herds that affects the paternal half-sisters. Estimates of c2 for sires in artificial insemination were similar to those of sires in natural service (about 0.11). This environmental correlation is large enough to be important in estimating breeding values of sires. A nonlinear function for the regression of one sample of daughters on an independent sample of daughters of the same sire was developed that included c2 and h2 Terms. Hartley's modified Gauss-Newton method was then used to obtain simultaneous solutions for the two parameters.