CONSIDERATIONS FOR IMPROVING FEED EFFICIENCY IN DAIRY CATTLE

Feed efficiency is an elusive concept with multiple definitions. We have made tremendous progress in gross feed efficiency by selecting for increased milk yield. Yield expressed as a multiple of maintenance is an important determinant of gross efficiency below 5x maintenance levels of production, and can be achieved by increasing yield with constant body size and maintenance requirement, or decreasing body size and maintenance requirement while maintaining production. At higher ratios of milk yield to maintenance, direct selection for improved marginal efficiency may be more important for improving gross efficiency. Genomic tools, combined with direct measure feed efficiency phenotype in a large sample of cows, provides a way to select future sires for improved marginal feed efficiency. In addition, data collected broadly on feed efficiency phenotype will allow us to test our current theories on how body size affects maintenance costs and feed conversion efficiency in modern Holsteins. Other management techniques that increase the ratio: use of feed for milk/herd maintenance use; are also important. In addition N efficiency can be increased (and inefficiency and waste decreased) using current knowledge and more precise feeding of multiple rations throughout lactation, but implementing management of cows, labor and information present some obstacles to implementing grouping and group specific feeding on all farms.