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Relative Merits of Five Measures of a Dairy Sire's Transmitting Ability^{1, 2,}

Department of Animal Industry, North Carolina State College, Raleigh

ABSTRACT

Lactation milk and fat records of 6,949 daughters, 6,201 different dams, and the contemporary D.H.I.A. herd averages of 2,420 herds were studied, to compare five measures of a dairy sire's transmitting ability. They were the daughter average, daughter-dam difference, equal-parent index, daughter-contemporary herd difference, and daughter-contemporary-herd index. The daughters and dams were included in the D.H.I.A. proofs for 350 Guernsey and 486 Holstein sires used in artificial-breeding associations, and whose proofs were published for 1949–1951. A variance component analysis did not reveal any marked superiority for any of the measures, as determined by the percentage of the total variance comprised by the sire component for each of the measures. Sufficient data for the Holsteins were available for an empirical check of the reliability of these five measures. The simple daughter average appeared to be about as reliable as the equal-parent index or the daughter-herd index to predict future daughters' production for milk or fat. The D.H.I.A. herd average included the daughter in question and reduced the magnitude of the sire component for the herd measures. Use of a contemporary-herd average, which excludes the daughter in question in the two daughter-herd measures, should improve their merit as measures of a dairy sire's breeding value compared to the other measures in this study.

¹ Contribution from the North Carolina Agricultural Experiment Station and published with the approval of the Director of Research as Paper No. 872 of the Journal Series.

² The data in this paper were taken from a dissertation presented by the senior author to the Graduate School, North Carolina State College, in partial fulfillment of the requirements for the degree of Doctor of Philosophy, 1955.

³ Present address: Department of Dairy and Animal Science, University of Massachusetts, Amherst.