The global Holstein breed, which is composed almost completely of American Holstein genes, has largely replaced other breeds of dairy cattle in much of the world. Production and conformation traits have been emphasized for improvement of Holsteins because of moderately high heritability and ease of data collection. However, female fertility, calving ease, calf mortality, health, and survival have been ignored for the global Holstein breed until very recently. The decline of Holsteins for the functional traits, coupled with increases of inbreeding of Holsteins internationally, has resulted in tremendous global interest in crossbreeding by commercial dairy producers. Purebred sires will continue to be sought to breed almost all dairy heifers and cows for crossbreeding. Most crossbreeding systems with dairy cattle will make use of three breeds to optimize the average level of heterosis across generations.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume , , 01.01, 2006
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