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Special report: Genetics help quest for improved dairy cows

Published on June 3, 2011 3:01AM

Last changed on July 1, 2011 11:39AM

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Capital Press

For dairy farmers, mapping the bovine genome in 2009 has led to a world of possibilities.

The information gained from mapping the genes of cows will one day be used to select dairy cows with greater milk production capabilities, researchers say.

In addition, scientists are looking into ways that cattle can be bred to resist diseases such as bovine respiratory disease.

"I think there's great potential that we haven't begun to realize yet," said Terry Lehenbauer, a University of California researcher who's taking part in a multi-campus project looking at the potential for genetic resistance to bovine respiratory disease.

Scientists "are starting to make use of that new information in different ways," said Lehenbauer, the associate director of the UC's Veterinary Medicine Teaching and Research Center in Tulare, Calif.

For instance, some companies are beginning to offer genetic typing of cattle herds to determine genetically superior animals, Lehenbauer said.

Scientists have used the sequence to predict milk production in dairy cows with three times higher accuracy and at a small fraction of the cost of earlier methods, reports the USDA's Agricultural Research Service.

They are also now able to provide the information at birth rather than at 5 years of age, the ARS reports.

The studies continue two years after a U.S.-led international team of 300 scientists completed their six-year quest to sequence the bovine genome.

Researchers led by the National Institutes of Health and the U.S. Department of Agriculture reported their findings in 20 papers that appeared in the journal Science and other journals, including Genome Biology.

The scientists used the genetic sequence from a single Hereford cow and comparative sequences from six other breeds, looking for changes called single nucleotide polymorphisms -- SNPs -- which are markers that can help researchers identify favorable traits.

Among the scientists' findings:

* The genome of the domestic cow contains approximately 22,000 genes, compared to 20,000 to 25,000 for humans.

* The organization of human chromosomes is closer to that of domestic cattle than to those of rats or mice, which are often used in lab tests of drugs intended for people.

* Cattle chromosomes, like those of humans and other mammals, contain segmental duplications, which are large, almost identical copies of DNA present in at least two locations in a genome.

The genetic research is sure to have short- and long-term impacts, said John Champagne, the chief of dairy production medicine at the UC's Tulare center. In the short term, it's quickened the pace of breeding for specific traits, he said.

For the beef industry, the DNA data promises to be a useful tool as ranchers pick the best cattle for qualities like meat tenderness, weaning weight, reproductive efficiency and resistance to diseases that would require antibiotics to treat.

For dairy farmers, understanding the makeup of the genome could lead to more efficiency in producing milk -- not just a greater volume per cow but also with more protein or fat per gallon, said Michael Marsh, chief executive officer of Western United Dairymen.

Dairy farming today is already more environmentally friendly than it was decades ago, Marsh said. Today's 9 million dairy cows in the United States produce far more milk than the 28 million dairy cows that existed in 1944, he said.

Genetics will undoubtedly help the industry become even more efficient as it feeds a growing world population, Marsh said.

"There are some opportunities that are likely going to occur as a result of this mapping that are going to be gee-whiz," he said. "That's why it's important."

Research into disease resistance traits is "still in the very early stages," the UC's Champagne said. Among those is resistance to mastitis, which is "by far the biggest infectious disease and the costliest disease" in dairy cattle, he said.

Also under way is the bovine respiratory disease project, a five-year, six-university study led by Texas A&M University and including scientists at the University of California and Washington State University.

The scientists are working with animals in normal production operations rather than in a lab, said Michael Kahn, associate director of WSU's agricultural experiment station.

"This will potentially make for healthier cattle," Kahn said, noting that diseases contribute to both an animal welfare problem and to the cost of doing business.


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