An evaluation of single and multiple trait selection programs in the improvement of dairy cattle

The purposes of this study were to evaluate the responses obtained when dairy sires were selected for a single trait and for multiple traits and to compare the production responses from sires selected on the basis of AI and Non-AI progeny tests.

Data for this study were obtained from animals in the Middle Tennessee Experiment Station herd. The data included production information on 211 two-year-old Holsteins and type information on 206 of these animals. These animals were sired by 17 sires available in commercial breeding organizations. The sires in line one were selected by an index that assigned equal weight to the sum of the five udder descriptive traits and FCM expressed as predicted difference. The sires in lines two and three were selected for their breeding merit expressed as FCM, on the basis of their AX and Non-AX progeny test, respectively.

The expected superiority of line two over line one, based on sire summaries at the time of sire selection, was 553 pounds of milk, 21 pounds of fat, and 522 pounds of fat corrected milk. The observed superiority was 777 pounds of milk, 20 pounds of fat, and 560 pounds of fat corrected milk. Line three produced 1093 pounds less fat corrected milk, on the average, than did line two. These facts bear out the accuracy and desirability of the present sire proving procedures.

The superiority of line one in teats and fore udder suggest that progress can be made by use of the descriptive traits as a selection guide, however, the results of this study give rather strong indication that it is not economical for dairymen to select dairy animals on any trait other than milk production.