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

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Abstract
Environmental correlations (c 2) 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 midwesteru states. Both mature-equivalent and deviation rec- ords 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 c 2 for sires in artificial insemination were similar to those of sires in natural service (about 0.11). This environmental correla- tion is large enough to be important in estimating breeding values of sires. A non- linear function for the regression of one sample of daughters on an independent sample of daughters of the same sire was developed that included c 2 and h 2 terms. Hartley's modified Gauss-Newton method was then used to obtain simultaneous solu- tions for the two parameters.