Selection Practiced Among Dairy Cows. III. Type Appraisal and Lactation Traits

Abstract

Phenotypic selection among Holstein cows on the deviation of milk yield from the herd-mate average and type appraisal traits was investigated. The largest selection differentials in standard deviation units for the second, third, fourth and fifth, or later lactations were breeding trouble, incidence of mastitis, depth of body and udder attachments, respectively. An average index was constructed such that the efficiency of selection practiced was maximized for the type appraisal traits and yield deviations, simultaneously. The yield deviations had the largest standardized selection differentials for the first lactation among all 12 traits. Efficiencies of selection described by the index were larger than the efficiency of milk yield alone by .08, .22, .48, .28 and .39 for the first through the fifth or later lactations, respectively. The relative weights, independent of the variation of the traits, ranked the milk yield deviations first, second. ninth, sixth, and sixth, for the same series of lactation groups, respectively. The intralactation index indicated that milk yield had a weighting coefficient about twice as large as the second and third ranked traits, depth of body and dairy character.