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Environmental Correlation Between Paternal Half-Sisters for Milk and Milk Fat Production¹

Animal Science Department, Iowa State University, Ames 50010

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.

¹ Journal Paper J-6758 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project 1053, done in collaboration with North Central Regional Project NC-2, Improvement of Dairy Cattle Through Breeding.

² Present address: E. R. Squibb and Sons, East Brunswick, New Jersey 08816.