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Differences between Sires in Rate of Maturity of their Daughters¹

Department of Animal Science, Iowa State University, Ames

ABSTRACT

The within-sire regression of actual production on age at calving in first lactation measured rate of maturity. Only cows calving between 23 and 35 months of age and sires with more than 44 daughters were used. Regressions of production on age differed significantly among 28 sires and ranged from –9 to +258 lb of milk per month of age and from –4 to +11 lb of milk fat per month of age. There were also large differences between herds and years for this measure of rate of maturity. The effect of herds on rate of maturity was estimated to be from two to three times as important as the effect of sires.

¹ Journal Paper no. J-5187 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project no. 1053.

² Present address: Department of Animal Sciences, Washington State University, Pullman, Washington.