Correlated Response in Classification Scores Accompanying Selection for Milk Yield in Jerseys

Abstract

Daughters of bulls selected for PD milk (selection line) were compared to random bred controls at the University of Tennessee-USDA Dairy Experiment Station. Jersey classification data were divided: 1) 166 selection and 82 control cows scored under the categorical system (1971 to 1979); and 2) 152 selection and 45 control cows scored under Uniform Functional Type Traits Appraisal (1980 to 1984). Least squares analysis compared first parity scores, adjusted for age and stage of lactation, of selection line cows with those of controls. Type scores from both data sets were dependent variables in a mixed model including effects of date classified, line, and sire within line. Linear scores of selection line cows were higher for dairy character (82.4 vs. 76.1) and final score (76.9 vs. 73.6). Dairy character scores (86.2 vs. 84.7) were higher for selection line cows in the categorical subset. Line means for other nonlinearly scored traits were not different.For linear data, dairy character rating explained much of the variation in final score. Other important traits in this regard include front teat placement, fore udder, foot angle, and suspensory ligament. These results reflect emphasis placed on priority traits by the American Jersey Cattle Club.