Author
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Norman, H |
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Powell, Rex |
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Submitted to: Asian-Australasian Journal of Animal Sciences
Publication Type: Review Article Publication Acceptance Date: 7/15/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Extensive emphasis on milk and milk fat yields with no diversion for beef performance increased the yield efficiency of North American dairy cattle. Heavy demand for North American genetics followed national strain comparison trials in Poland, and U.S. dairy cattle and germplasm still is an important source of genetics for many countries. Genetic improvement has accelerated in many countries because of the implementation of sampling programs for young bulls and improved evaluation procedures. Rapid access to information and more frequent calculation of genetic information also are having a positive impact on genetic improvement. Traits other than yield should be considered in a breeding program, but those traits must have a reasonable opportunity for improvement and sufficient economic worth. Because of ever increasing efficiency, the world's milk supply comes from fewer cows each year. However, no decline in the rate of genetic improvement is apparent under current genetic practices; estimates of heritability are increasing, and a decline in yield efficiency is unlikely in the near future. As management improves, especially for subtropical conditions, many of the selection principles used in temperate climates will be adopted for more adverse environmental conditions, which should improve economic opportunities for those dairy breeders. Technical Abstract: Extensive emphasis on yield traits with no diversion for beef performance increased the yield efficiency of North American dairy cattle. In strain comparison trials of Holsteins and Friesians in Poland, offspring from U.S. and Canadian bulls ranked 1st and 3rd for milk yield. Heavy demand for North American genetics followed, and the U.S. dairy populations is an important source of genetics for many other countries as indicated by the origin of sires of bulls used in leading dairy countries. Genetic improvement has accelerated in many countries because of the implementation of sampling programs for young bulls and improved evaluation procedures; the number of young sires has doubled in the last 20 years. Rapid access to information and more frequent calculation of genetic information also have a positive impact on genetic improvement. Traits other than yield should be considered in a breeding program, but those traits must have a reasonable opportunity for improvement and sufficient economic worth (e.g., longer productive life or trouble-free health) to be included in selection decisions. Because of ever increasing efficiency, the world's milk supply comes from fewer cows each year. However, no decline in the rate of genetic improvement is apparent under current genetic practices; estimates of heritability are increasing, and a decline in yield efficiency is unlikely in the near future. Numerous opportunities exist for improving milk recording and initiating genetic improvement programs in countries that currently have limited selection and breeding activities. As management improves, especially for subtropical conditions, many of the selection principles used in temperate climates will be adopted for more adverse environmental conditions. |
