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Milk Component Yields versus Concentrations as Selection Criteria to Improve Milk Revenue¹

The Ohio State University, Columbus 43210

ABSTRACT

Quadratic milk pricing formulas based on total yield with concentration differentials for fat and protein can be linearized to price milk based on yields of carrier, fat, and protein. Selection responses for a quadratic milk revenue function and an equivalent linear milk revenue function were compared in each case using in the selection indices those traits in the corresponding milk revenue function. Using observed variance and covariance estimates, selection responses for linear milk revenue functions were an average of 11% greater than responses for corresponding quadratic milk revenue functions. However, when variances and co-variances for milk component yields were predicted from those observed for milk yield and component concentrations, differences in selection responses for linear versus quadratic milk revenue functions averaged only 2.7%. Therefore, it was concluded that inconsistencies among variance and covariance estimates for milk component yields and concentrations are sufficient to explain the observed disparities in selection responses for equivalent linear and quadratic milk revenue functions. Higher levels of internal inconsistency among trait parameter estimates were found when using averages of available literature estimates than when using estimates for all traits determined in a single study. The use of linear milk revenue functions is recommended to clarify the transmission of market signals to dairy cattle breeding programs.

¹ Contribution to NC-2, Improving Dairy Cattle, with special emphasis on selection.

² Current address: Centre for Genetic Improvement of Livestock, Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1.

³ Salaries and research support provided partially by state and federal funds appropriated to The Ohio Agricultural Research and Development Center, The Ohio State University. Journal Article Number 107-89.

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