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New Genetically Modified Cow is Resistant to Mastitis Strain

By Cheryl Dorschner Article published April 13, 2005

Jersey girl: UVM researchers created a modified gene that USDA scientists implanted into cow embryos, creating animals more resistant to a strain of mastitis. The cow shown here, GEM, appears to be immune to the bacteria. (Photo: Stephen Ausmus/USDA)

Collaborating scientists from UVM and the United States Department of Agriculture have, for the first time, produced genetically modified dairy cows resistant to a form of mastitis, the widespread and painful bacterial infection of cows’ udders that is difficult to control with antibiotics.

David Kerr, assistant professor of animal science, and Robert Wall, principal investigator and USDA animal physiologist, and colleagues published their results in the current issue of Nature Biotechnology.

In his UVM lab, Kerr produced the modified gene that enables animals to produce a naturally occurring enzyme, lysostaphin, in their milk. Kerr sent the gene to the USDA in Beltsville, Md., where Wall's group inserted the gene into Jersey embryos. So far, five transgenic cows and one bull carrying the lysostaphin gene have been produced. Among these, three cows underwent testing; all showed resistance to Staphylococcus aureus, and one never became infected. Fourteen percent of the mammary glands of transgenic cows were infected compared to a 71 percent rate of infection in nontransgenic cows in the experiment. Lysostaphin in the cows’ milk breaks down the cell walls of the S. aureus bacteria, a major cause of mastitis.

“This is an important step toward helping dairy farmers,” says Kerr. “Every year, U.S. farmers lose $2 billion to mastitis in discarded milk, veterinary costs and the like. This approach could cut that substantially. This research also addresses two other issues: current reliance on antibiotics and cattle welfare — this is a painful infection for cows.” Since the disease is difficult to cure with antibiotics, it is often controlled by removing chronically infected cows from the herd.

A promising avenue
Although lysostaphin does not kill all mastitis-causing bacteria, these results suggest that it might be possible to control other harmful bacteria in dairy cattle with different antibacterial genes.

“This research is an important first step in understanding how genes can be used to protect animals from disease,” says Edward Knipling, administrator of USDA's Agricultural Research Service.

As with milk from cows with mastitis or receiving antibiotics, milk from these genetically modified cows is not approved for human consumption. Use of milk containing lysostaphin would require federal regulatory approval after food-safety testing. This effort is at the early stages of research and development.

“This is a milestone for UVM and puts us in the forefront among research institutions,” says Rachel Johnson, dean of the College of Agriculture and Life Sciences. “Our partnership with USDA contributes immensely toward the health of cows, potentially saving billions of dollars in dairy farmer costs and moving scientific inquiry forward.”

“It was brilliant of UVM provost and animal scientist John Bramley to recognize this staph bacteria’s potential a decade ago,” says Thomas McFadden, associate professor and interim chair of the Department of Animal Science. “His and others’ research paved the way for this significant accomplishment. David Kerr has carried on and improved that initial work to bring it to recognition by one of the top journals in the field.”

Future studies, Kerr says, will include developing similar defenses against other pathogens that affect dairy cattle and gauging the milk’s ability to effectively produce dairy products, such as cheese and yogurt.