NUTRIENT-REQUIREMENTS AND FEED COSTS ASSOCIATED WITH GENETIC-IMPROVEMENT IN PRODUCTION OF MILK COMPONENTS

Dietary requirements for NE(L) and absorbed true protein were summariz ed for marginal production of milk components because of genetic impro vement through selection. Shelled corn and soybean meal were used to m eet marginal nutrient requirements and were assigned variable concentr ations of absorbed true protein, depending on rumen-available energy a nd protein. Mean ratios among national averages for shelled com to mil k prices and soybean meal to milk prices (DM: standardized milk, dolla rs per kilogram) over a recent 25-yr period were .52 and 1.20, respect ively. Stability of these relationships over time permits estimation o f feed costs from milk price as prices inflate. Feed costs per kilogra m of component, expressed as kilograms of standardized milk with equiv alent value, were 1.00 for lactose, 1.89 for fat, and 3.49 for protein . Costs of milk protein were higher if production of absorbed true pro tein was limited by rumen-available energy, suggesting that selection for fat or lactose, in addition to protein, may be beneficial. High fe ed costs for milk protein indicate a need for adequate compensation to producers for milk protein and consideration of feed costs during sel ection. A net value index is proposed that considers feed costs associ ated with marginal production of individual milk components.