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Selection Differentials

Department of Dairy Science, Virginia Polytechnic Institute and State university, Blacksburg 24061

ABSTRACT

Introduction

At the 58th annual meeting of the American Dairy Science Association in June, 1963, C. R. Henderson (6) outlined many principles in selecting young sires to sample in artificial insemination (AI). These principles have not been altered or extended significantly during the intervening 11 yr. Our progress since that time has been through practical application of these principles and through realization that breeding and identification of superior bulls require a commitment strong enough to weather the discouraging errors which are certain in choosing young bulls to sample. My purpose is to assess briefly the strength of this commitment in the recent past as evidenced by the intensity and efficiency of selection in choosing young bulls to sample and in selecting proven bulls for return to extensive AI use. I will attempt to compare the observed intensity of selection, measured in terms of the selection differential for milk yield, with that which might be achieved if our goals were simply defined and universally agreed upon.