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Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/29/2004 Publication Date: 10/1/2004 Citation: Van Raden, P.M. 2004. Selection on net merit to improve lifetime profit. Journal of Dairy Science. 87(10):3125-3131. Interpretive Summary: Genetic selection has made dairy cows more profitable. Terms defined by early animal breeders are still very useful and are now applied to very large populations. Selection indexes provided by USDA included yield traits beginning in 1971, productive life and somatic cell score in 1994, conformation traits in 2000, and cow fertility and calving ease in 2003. This latest revision should result in faster progress worth $5 million per year nationally, with improved health and fitness, but slightly less progress for yield. Inclusion of more traits provides breeders a more accurate summary of lifetime profit. Many other nations provide selection indexes similar to U.S. net merit. Technical Abstract: Genetic selection has made dairy cows more profitable producers of milk by changing a number of income and expense traits. Yield and conformation traits are more heritable than longevity, fertility, and health traits, but many traits may deserve selection because of large economic values and coefficients of variation. Selection indexes provided with USDA evaluations included yield traits beginning in 1971, productive life and somatic cell score beginning in 1994, and conformation traits in 2000. In August 2003, cow fertility and calving ease were included in net merit calculations. Selection using the new formula should result in faster progress for several measures of health and fitness, but slightly less progress for yield. Breeders may prefer to select for fertility instead of longevity because cows have several fertility records but only one longevity record, which is incomplete until the end of life. Fertility and longevity evaluations have similar reliability even though the heritability of longevity is greater. Multiple selection indexes are needed for different production systems and markets; milk volume has positive value for fluid use, but negative value for cheese production. Breeding programs must consider future costs and prices, but these are difficult to estimate. Lifetime profit can be estimated more accurately if more traits are evaluated. Many other nations have derived selection indexes similar to U.S. net merit. |
