Origin and evolution of genetic evaluation methods of linear type traits and production traits of U.S. Holstein cattle and their role in selection
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The aim of this paper was to discuss the origin of the Holstein breed and the evolution of methods of genetic evaluation for both type and production traits and how they were applied to selection in order to form the unique animal that is the U.S. Holstein today. This paper starts at the origin of the breed in Europe and its first importations to the United States. It then goes on to explain how its high milk yield and other more historically centered factors made it a popular animal throughout the United States and eventually the world. The Second part of this paper explains the origin of the concept of True Type and Descriptive Classification. It shows how these systems evolved into the Linear Type Classification and Final Score of the breed today. The third part of this paper illustrates how the methods of genetic evaluation that attempted to combine ways to select for both yield and type traits evolved, from the daughter/dam comparisons of the 1920’s to the Animal Model and Composite Indexes of today. The Last part of this paper shows how the same advances in production made through genetic selection led to a decrease in the health and fertility traits of the breed, and also indicates how selecting animals for type, regardless of assumptions otherwise, did not counteract this decline. The paper concludes that the time has come to switch the emphasis of selection from production and type traits to health and fertility traits, and that regardless of the fact that there is a close genetic relationship between production and fertility, there is in fact hope that this downward decline in fertility and health can be reversed with the help of genomic selection.