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Genetic and Environmental Factors in Dairy Sire Evaluation. III. Influence of Environmental and Other Extraneous Correlations Among the Daughters¹

Department of Animal Science, Iowa State University, Ames

ABSTRACT

The practice of regressing dairy sire proofs for the numbers of daughters included and for the average correlation among those daughters has been gaining wide acceptance in recent years. However, the contributions of environmental and other extraneous correlations to the regression factors being used have been generally neglected. Justification for this has been based largely on the assumption that, when deviation records are used, the effects of these residual correlations in artificial insemination (AI) bull proofs are of no practical significance.

In several studies with deviation records, the expected correlations of the separate proofs of bulls were computed on the assumption of zero residual correlations among the daughters represented in each proof. The wide discrepancies found between the expected and sample correlations raise some doubts as to the general validity of this assumption.

¹ Journal Paper No. J-4975 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1053. This research was part of North Central Regional Project NC-2.

² Present address: Department of Dairy Science, University of Illinois, Urbana.