Little genetic improvement can be achieved without objective measurement of traits targeted for improvement. Countries vary considerably in percentage of cows that are in milk-recording programs. In the United States, slightly less than 50% of dairy cows are enrolled in a dairy records management program that supplies performance records to the national database, and parentage of only about 65% of those cows is known.
The first traits to be evaluated nationally in the United States were milk and butterfat yield and percentage. During the 1970s, national evaluation of protein yield and percentage, conformation traits, and calving ease (dysto-cia) began. Evaluations for longevity (productive life) and mastitis resistance (somatic cell score) became available during the 1990s. The most recent trait to be evaluated by the U.S. Department of Agriculture is daughter pregnancy rate, which is a measure of cow fertility.
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