Only a small percentage of dairy cows that are culled from herds are believed to harbor the pathogenic Escherichia coli O157:H7 bacteria. But the potential for contamination is enough to launch two Cornell University- based programs that could help beef producers nationwide avoid government overregulation while ensuring a healthful food supply.

The New York State Cull Dairy Cow Project, based in the College of Veterinary Medicine's Diagnostic Laboratory, is testing culled dairy cows just before slaughter at the packing plant -- and tracing the animals' history back to the farms to learn why some cows harbor the bacteria while most do not.

The New York Beef Safety and Quality Assurance Program hopes to persuade dairy farmers that, as a cow's milk-producing days wane, she is still part of the food supply and should move into the food chain in good condition.

"ECO157 is not one of the common E. coli, but, unlike the others, some people can die from the O157:H7 strain," said the Diagnostic Laboratory's field epidemiologist, Christine A. Rossiter, V.M.D., referring to the E. coli strain in improperly handled hamburger that killed three patrons of a Washington state restaurant in 1993.

"Food handling practices every step of the way -- from the packing plant, to the distributors and retailers, to your kitchen counter -- are important factors in fostering or suppressing the growth of bacteria," Rossiter said. "You can't blame the cows for everything, but if this bug is getting into the food supply from the farm, we want to find out how much there is and how we can reduce its occurrence." "Culls" are dairy cows that are removed from the milking herds for any reason, most commonly because they're not producing enough milk to justify their upkeep. In New York, the nation's third largest dairy state, about one-third of the dairy herd -- about 175,000 cows -- are culled each year. Because meat from older dairy cows is not tender and marbled enough to be prime cuts of beef, much is ground for hamburger.

"Cull cows are a huge resource of hamburger in this country, where 50 percent of the beef we consume is hamburger," said Ted C. Perry, the beef cattle extension associate in Cornell's College of Agriculture and Life Sciences. New York's culled dairy cows account for three-quarters of all beef produced in the state; most of the 10.5 million pounds of hamburger eaten by New Yorkers each year comes from former dairy cows.

A preliminary survey, conducted last year at a major Northeast packing plant by the Cornell researchers with support of veterinary and field staff of the New York State Department of Agriculture and Markets, found ECO157 in only about 1 percent of 1,600 culled dairy cows. An earlier survey of dairy heifers, conducted in 28 states by the U.S. Department of Agriculture, found ECO157 in almost 4 percent of the young cows and about 5 percent of dairy herds. A similar prevalence of 1 percent has been found in cow populations by other researchers.

"This is not a 'cow disease' and it doesn't seem to affect cattle one way or another," said Rossiter, an expert in paratuberculosis and other cattle-borne infections that are prevented and controlled by good management practices. "We don't know why some animals have ECO157 and others don't, but dairy and beef cattle may be a 'reservoir' for this infection on its way to humans."

"Forget the needle in the haystack. You're talking about the tip of the point of the needle -- an extremely small amount of E. coli somewhere in tons of beef," Perry said, explaining one reason the federal government simply cannot test everything for ECO157. "Even 1 percent of a packing house output is truckloads of beef."

A better strategy is preventing any contamination from animals that enter the food supply, the Cornell researchers propose, and that view is shared by their supporters and collaborators in this project: the New York Beef Industry Council and the New York Cattlemen's Association, the New York State Department of Agriculture and Markets, and the USDA's Food Safety Inspection Service (FSIS).

So the cull cow project is going back to the farm. Sixty New York dairy farm operators -- 30 who sent at least one ECO157-positive cow to slaughter and 30 randomly chosen operators who did not -- are being interviewed in a search for risk factors that may be associated with ECO157 shedding. Cows that are most likely to be culled in the near future will be tested for ECO157, and farm operators will be asked about each cow's history, including its age, physical condition, health status, nutrition and milk production. Questions about overall farm management, housing and culling policy may tell the researchers why just a few cows shed the organism -- a knowledge that may lead to recommendations.

Fecal samples of cows, both at the packing house and on the farms, will be taken for six months in the warm part of the year and tested for ECO157. Pre-slaughter cows will be evaluated for physical condition, as well as for cleanliness of their hides (bacteria in fecal matter on the hides can be transferred to the carcass when the hide is removed).

Of particular interest is the culled cows' travel and ownership history, because animals that are stressed may be more likely to shed the bacteria. The Cornell scientists want to know if the stress of traveling from livestock auctions, where the original owner sells the culled animals, to the slaughterhouse is greater when cows pass through several intermediate hands and several cattle trucks. Each change of ownership adds another identifying "back tag" to the cow, Perry noted, "and some of these animals look like used billboards, they have so many tags." Meanwhile, Perry is taking the Beef Safety and Quality Assurance Program to cattle producers around the state. In workshops with farm owners and veterinarians, many held in cooperation with Empire Livestock Markets, Perry delivers the message: "There are dollar-and-cents reasons to cull and sell dairy cows while they are still in good condition." The temptation, he said, is to keep animals in the herd as long as they are producing milk, "even though they may not be breaking even on the cost to produce it." The economics of the cull/don't cull decision can be complex, especially when beef prices are low and any amount of milk adds something to the farmer's milk check, Perry acknowledges. He hopes to help farmers consider the bigger picture.

"Producers are very conscious of food quality -- in beef if they raise beef cattle or in milk from dairy cattle -- but not everyone thinks of cull cows as a food product," Perry said. "However, we are entering the era of smart, voluntary self-policing of the industry -- as a better alternative to more government regulations -- for all safe-food issues, not just for E. coli," Perry said.

"The beef industry already meets higher standards than the government requires because the market demands a top quality, healthful product," Perry said, "and preventing E. coli in beef fits into that scheme." Once the New York state study - - together with concurrent studies in other areas of the country -- identify the risk factors for E. coli contamination, beef producers will know what to do next. They will be able to add to the good-management practices that ensure herd health, profit and quality products for the marketplace.

"That culled cow is somebody's hamburger," Perry tells farmers. "As a producer you have a responsibility to make sure that meat can be eaten safely without it having to be inspected by the government."