Association between milk breeding values and phenotypic conformation traits in pure-dairy and dual-purpose cows

The association between milk yield breeding values and phenotypic conformat ion scores on 50 325 Ist calf heifers registered in Belgium between January 1980 and November 1996 has been examined. Logistic regression was used as a better alternative than correlation analysis to study the association. Re sults of the stepwise procedure showed that (1) high stature (2) shallow bo dy, and (3) wide and deep udder with strong ligament and widely placed fron t teats were more frequent in dual-purpose cows with milk breeding values > 1500 than in dual-purpose cows with lower milk breeding values. In pure-da iry cows, frequency of (1) tall, nervous, fast milking cows, with (2) wide, deep udders with strong ligament and strong fore udder attachment, and wit h (3) steep foot angle was higher in cows with milk values >2200 than in pu re-dairy cows with lower milk breeding values. In both breed and for all tr aits, the odds did not vary linearly across the conformation categories. Th erefore, logistic regression seemed more appropriate to study association b etween conformation traits and milk breeding values than other methods that assume equal differences between adjacent scores on any part of the scale. It is also suggested that conformation characteristics be used as indicato rs of milk genetic potential for first parity cows, when accurate informati on on milk breeding Values is lacking.