January 12, 2001

USDA's Agricultural Research Service and University of Vermont (UV) researchers have produced a clone of a pure-bred Jersey cow whose cells may offer a biotechnological defense against mastitis disease. Geneticist Kevin Wells of ARS said it will be at least another year before the cow, named "Annie" and born last March, begins producing milk and scientists can begin testing for mastitis resistance. Though not the first cow clone, Annie is the first to be genetically altered with a gene for an agricultural application.

Mastitis costs U.S. dairy farmers about $1.7 billion annually, including lost milk revenues, said Wells, with ARS' Gene Evaluation and Mapping Laboratory at Beltsville. About 30% of all mastitis cases in dairy cows are caused by Staphylococcus aureus bacteria that destroy milk-secreting cells in the animal's mammary gland. But scientists hope that Annie will resist such cellular attacks by secreting an added protein called lysostaphin.

Antibiotics are effective only in about 15% of cows infected with S. aureus, so dairy producers are forced to cull these cows from their herds. But lysostaphin may offer an alternative defense bioengineered right into the animal's cells.

"We're also trying to identify naturally occurring resistance genes, though very few of them have been found," noted Vernon Pursel, the GEML's research leader. Whether bioengineered or naturally occurring, he said, "resistance would lessen mastitis's financial drain, and provide the added public health benefit of reduced antibiotic usage."

In 1999 trials with seven transgenic strains of lysostaphin-producing mice, the protein effectively killed S. aureus bacteria in both the genetically modified rodents' mammary glands and milk, GEML physiologist Robert Wall said. He and David Kerr of UV's Animal Sciences Department in Burlington, report the results in January 2001 issue of the journal Nature Biotechnology.

S. aureus was targeted by scientists because it is among the most virulent of mastitis causing pathogens, and causes about 30 percent of all infections in cows. The gene for lysostaphin--interestingly--comes from a benign species of Staph--S. simulans--that competes with its virulent cousins.

Large-scale testing of lysostaphin mice in the lab will help researchers learn whether results observed in these transgenic rodents will apply to Annie and her offspring. Practical application of the cloning technology is several years off, however, Pursel said. First, a number of questions must be thoroughly researched.