Modern dairy cows are profitable if milk and beef income exceed feed, labor, housing, breeding, veterinary and other expenses over the cow’s lifetime. In the beginning, cows produced milk only for their calves. After cattle were domesticated, specialized breeds were developed with improved dairy and/or beef production. Selection focused on hair color, other unique breed features, conformation, and simple phenotypic measures of production. Dairy Herd Improvement programs have recorded costs for nearly 100 years, but until recently only income traits were evaluated genetically. As more traits were measured and accuracy of evaluations increased, selection indexes grew in importance. USDA selection indexes provided since 1971 and Holstein Association USA Type-Production Index (TPI) provided since 1976 are summarized in Table 1. Selection for lower SCS is listed with positive values. Relative emphasis equals economic value times standard deviation (SD) divided by the sum of the absolute values of these products, then multiplied by 100. Relative values were obtained using SD of true transmitting abilities in USDA indexes and SD of predicted transmitting abilities (PTA) in TPI. Other U.S. breed associations publish Production-Type Indexes with different relative values
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 1, , 1.21, 2002
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