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Estimation of Maximal Heritability Parameters in Dairy Cattle Breeding¹

Department of Animal Science, Iowa State University, Ames

ABSTRACT

Heritabilities of milk yield, milk fat yield, and milk fat percentage, all expressed as deviations, and the genetic correlations among these traits were estimated from the within-sire regressions of daughter on dam. The data were grouped into a discontinuous form and phenotypic scales for each of the traits were found on which the heritabilities of the traits are maximized. The maximized heritability estimates were 0.366, 0.376, and 0.566 for each of milk yield, milk fat yield, and milk fat percentage, respectively. Although all three are larger than estimates obtained by using additive scales, the differences are not large enough to be of practical significance. The three new scales are close to additive in form, although there is an indication of possible nonadditivity in the scale for milk fat percentage deviation.

¹ Journal Paper no. J-5607 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project no. 1053. This is a part of the Regional Dairy Cattle Breeding Project NC-2.

² Present address: Ruakura Agricultural Research Center, Hamilton, New Zealand.