Genetic Improvement – an Historical Perspective
نویسنده
چکیده
Dairy producers have selected for higher milk production for many years. Genetic improvement causes an average Holstein cow born in 2003 to produce over 7,000 pounds more milk in one lactation than her ancestor born in 1960 produced. Type traits, particularly udders and feet and legs, have also improved because of intensive selection. However, the health and fertility of dairy cows cannot be included among these success stories. Genetic trend was responsible for half of a 9-point decline in pregnancy rate in Holsteins between 1960 and its low point in 1995. Dairy-cattle breeders responded by developing national genetic evaluation programs for a number of fitness traits in recent years. This publication documents the genetic evaluation systems for these traits. It also explains a strategy to make economically sound genetic improvements simultaneously in production, type, and fitness traits through use of a selection index to locate outstanding bulls in AI service. The genetic evaluations discussed in this document already exist, but changes to existing systems as well as evaluations for additional traits should be expected in the coming years.
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