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

Phenotypie selection among IIolstein 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 seeond, third, fourth and fifth, or later lactations were breeding trouble, incidence of mastitis, depth of body and udder attachments, respectively. An average index was eonstrueted 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. Effieieneies 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 intralaeration index indieated that milk yield had a weighting coefficient about twice as large a~ the second and third ranked traits, depth of' body and dairy character.