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Estimating the Heritability of Type Classifications of Dairy Cattle

Department of Dairy Science, University of Illinois, Urbana

ABSTRACT

An analysis of type classification data involving 2,810 daughter-dam pairs was made to determine what numerical values the five grades of Excellent, Very Good, Good Plus, Good, and Fair should be given when estimating the heritability of type. The results indicated that an arbitrary system of consecutive numerical scores was as accurate as scores derived from the data.

Estimates of heritability of type were obtained by including all of the daughters of a dam in the covariance analysis. The following four methods of calculating the regression coefficients were compared: 1 and 2, the weighted and unweighted regression of the means of daughters records on dam's record, 3, repeating the dam's record with each daughter's record, and 4, adjusting the degrees of freedom in the crossproduct terms for the dams with more than one daughter. The resulting heritability estimates were approximately the same; consequently, the method of repeating the dam's records with each daughter's record seems sufficiently accurate and has the advantage of being easy to compute.

¹ Agent of the Dairy Husbandry Research Branch, USDA.