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Butterfat Production, Reproduction, Growth, and Longevity in Relation to Age at First Calving¹

University of Wisconsin

Abstract

A previous report³ has shown that the productive period from first calving to 84 months of age was enough longer for early calvers to more than compensate for the effects of less maturity on production in the first few lactations. The data provided little or no information on the relation of age at first calving to longevity, lifetime productivity, reproductive efficiency, or growth. The present data, include all cows that were retained until first calving in two large purebred Holstein herds in which all cows were milked three times daily throughout life. These records provide pertinent information on some of the questions which were not answerable from the previous data.

Sources of Variation in Age at First Calving

Age at first calving is completely determined by the age at first service and the interval between first service and conception. The association of both age at first service and interval from first service to conception with age at first calving was essentially linear.

¹ Paper from the Department of Genetics, Agricultural Experiment Station, University of Wisconsin, No. 272; published with the approval of the Director of the Station.

² The authors wish to acknowledge the assistance of personnel provided by the Natural Science Division of the Work Projects Administration.