Differences between Sires in Rate of Maturity of their Daughters

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Abstract
The within-sire regression of actual production on age at calving in 1st 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 ranges 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 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 2 to 3 times as important as the effect of sires.

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