Prediction of Transmitting Abilities for Productive Life and Lifetime Profitability from Production, Somatic Cell Count, and Type Traits in Milk Markets for Fluid Milk and Cheese

¹ Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061-0315

Two net income functions were constructed to reflect differences in value of carrier, protein, and somatic cell score (SCS) between milk markets for fluid milk and those for cheese. Individual costs were for production of carrier (water, lactose, and minerals), fat, and protein. Totals for net income from a lactation were adjusted for the opportunity cost of postponed replacement using all herdmates on test. Heritabilities and correlations were estimated with a multiple-trait sire model using 52,688 registered and grade (24%) cows that were classified daughters of 844 bulls included in the Sire Evaluation for Type program of the Holstein Association of America. Although the genetic correlation between the net income traits was high (0.92), the resulting economic weights were quite different. Indexes to select for net income for a fluid milk market weighted milk production much more than it weighted fat or SCS and selected against protein yield. Indexes for a cheese market gave more weight to milk components, SCS, and traits related to productive life. The removal of some type traits had little effect on the evaluation of either net income trait. In contrast, weights for prediction of productive life from SCS and the production and type traits became more stable when strength, fore udder, and rear udder height were removed. Removal of some of the type traits that were used for prediction reduced multicollinearity and the variance of weights without sacrificing accuracy.

Key Words: net income • productive life • somatic cell • score • lifetime merit

Submitted on June 10, 1996
Accepted on November 18, 1996

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