Efficiency of index selection for dairy cattle using economic weights for major milk constituents

Abslracl A breeding objectivc (aggregate genotype) for dairy cattle based on returns, net of feed costs, from yield of fat, protein and carrier (the non-fat, non-protein component of the milk) was developed. Returns were estimated using a forecast of the future Australian dairy market structure, and fecd costs were estimated from the metabolizablc energy required to produce each of three milk components. The effects of erors in forecasting future conditions on economic weights and efficiency of index selection of sires were examined. Economic weights varied widely when subject to errors in the price of milk components within markets, errors in the export price for milk and errors in feed cost. Selection based on an optimal index of sire expected breeding values for fat, protein and milk was sensitive to low export market prices, high feed costs, high protein price and high carrier price. This index was quite insensitive to variation in prices and costs opposite in sign to those above, to variation in milk prices on the domestic markets, and to variation in the size of quotas on domestic markets.