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Procedures for selecting sires are compared in terms of making maximum genetic progress in economic merit. A quadratic index, a simplified form of the quadratic index and a linear index to evaluate economic merit, and a restricted index to improve milk as much as possible while holding milk fat percentage constant, all result in nearly equal expected genetic progress in economic merit. Selection for milk production results in less expected genetic progress in economic merit, the extent of the decrease depending on the economic value of milk production at a given base test and on the test differential.
Evaluation of sires for economic merit depends on the economic values and on the means of milk production and test. The simplified form of the quadratic index appears to be a useful index, since sire economic merit index values can be calculated for any mean levels of milk production and test and for any economic values, once index values for milk and test have been found.