Ranking Dairy Sires by a Linear Programming Dairy Farm Model

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Abstract
Dairy sires were ranked for overall merit by an average daughter''s contribution to farm net profit. Biological characteristics of sires and economic factors of a dairy farm were linked by linear programming. Availability and constraints of resources were in the model. Average daughter''s returns over variable costs attributable to sire proofs for several traits were the measure of sire''s net merit. The index of total economic merit for sires was the amount of change of net profit by milking progeny of different sires. Ranking considered sire''s contribution to milk yield and feed intake of daughters caused by variations of proofs for milk, fat percent and size, sire''s nonreturn rate, veal calf sales of the offspring and labor costs of slow vs. fast milking daughters. Size of quota for daily milk shipments, cow housing capacity, labor for milking and milk tank capacity were critical in determining ranking and forced greater emphasis on traits other than milk yield. Correlations between sire ranking on returns over variable costs and sire proofs were highest for milk and significant for fat percent, milking speed, size and nonreturn rate. These traits had high standard partial correlations with and explained most of the variation of the index of total economic merit. This method aims at maximizing farm profits and may be applied to rank dairy sires on a national basis or to select sires for specific dairy farm operations. Production dollar index ratings on the same sires were closely correlated (-0.87 to -0.96) with profit index ranking but are potentially misleading if constraints exist that limit maximum milk output per farm.