Animal Science Department
Date of this Version
A selection index combining milk and beef production traits, such that progress in aggregate economic value is maximized, was constructed for Holstein bulls. The index for milk was IM = 1.11X1 + .997X2 while the index for beef trait was IB = .008X1 + .619X2 where X1 is the daughters' average lactation yield (kg) and X2, bulls' body weight at 15 mo (kg).
The relative genetic progress from simultaneous selection for milk and beef traits with different emphasis was estimated. Expected genetic progress in beef production (body weight at 15 mo) declined with increasing selection on milk and vice versa. Expected genetic progress, however, did not fall below one-third of maximum genetic progress (100%) for either milk or beef, regardless of the emphasis of selection.
Based on current milk and beef values, ignoring milk and selecting solely for beef would give the highest genetic progress in total economic value but quite slow genetic progress in total protein production. Ignoring beef and selecting solely for milk would give the highest genetic progress in total protein production and a fairly high genetic progress in total economic value. A 1:7 beef to milk emphasis per standard deviation seems to be most appropriate since it results in large genetic progress in both total protein and total economic value.
Published in Journal of Dairy Science. Copyright © 1972 American Dairy Science Association. Used by permission.