The Long, Hard Road to Beef Safety: Beef Recalls Spike in 2007

E. coli O157:H7 has been described as ubiquitous in dairy and beef cattle and is present on most farms and feedlots. Feedlot cattle have a strong chance of E. coli O157:H7 contamination because most cattle are obtained from large herds. In virtually every herd, some animals are shedding O157:H7. In addition, the animals are housed under crowded conditions, with or without efficient manure removal systems, a situation that provides this organism ample opportunity to persist and multiply.

USDA research has demonstrated a difference in the prevalence of E. coli O157:H7 in heifers, cull cows, and yearling cattle. Cattle weight, seasons of the year, herd management, and feedlot practices have been shown to affect prevalence as well. In an ideal world, slaughterhouse management should consider as their source of animals for slaughter only those farms and dairies that incorporate practices that reduce carriage of pathogens.

Cattle continue to be implicated as the reservoir for E. coli O157:H7. At present, control of entry and contamination from these pathogens in slaughter establishments is based to a large extent on sanitation procedures, control of cross contamination, and treatment of carcasses for visible contamination. Its widespread prevalence in cattle is a testament to the organism’s ability to survive for long periods—for months in water trough sediments—thus providing an ongoing source of exposure to cattle.

Vaccines, Feed Strategies

Effective vaccines for cattle would help. A Canadian company has spent more than five years trying to develop an E. coli O157:H7 vaccine. The vaccine is available to Canadian producers, but in September 2007 the USDA declined to approve its use in the United States. Even if this vaccine had been approved, the risk of cross contamination with other cattle would require segregation of livestock. This intervention wouldn’t work for the burgeoning multibillion-dollar organic meat market that has emerged within the past few years, however.

Other researchers are looking at changes in diet that would make the bovine digestive system less hospitable to pathogens. Strategies would include competitive exclusion, which involves the addition of a nonpathogenic bacterial culture to the gastrointestinal tract of food animals in order to truncate populations of pathogenic bacteria. Another strategy involves the use of probiotics—applying micro-flora to reduce pathogenic bacteria in the gut.

Another issue to consider is the source of some cattle feed. A viable alternative to motor oil and gasoline is ethanol, which is derived from grains. The production of ethanol has resulted in a symbiotic relationship between ethanol producers and cattle ranchers. Ethanol plants need to dispose of the grain left over following their manufacturing process, and cattle ranchers need a cheap source of high-protein feed for their livestock. Today, a number of ethanol factories are being built next to feedlots.

Another source of feed, distillers’ grains, may be putting the public at risk. Several preliminary rounds of testing at Kansas State University (Manhattan, Kan.) recently showed that the prevalence of E. coli O157:H7 was about twice as high in cattle fed distillers’ grain compared with cattle on a diet lacking ethanol byproduct. Researchers are not sure why, but it is becoming clear that as ethanol continues to grow as an alternative fuel source, more cattle will regularly be fed distillers’ grain.

The Slaughterhouse Stop

Today, the majority of livestock are delivered to slaughterhouses by tractor-trailers, which should be cleaned after each delivery. Gross cross-contamination to livestock occurs if these delivery double-deckers and goosenecks aren’t cleaned after each delivery. In most cases, trailer cleaning is chronically neglected; it can certainly be improved upon. There are no USDA regulations requiring the cleaning of cattle trailers, either before or after transport of cattle; slaughterhouse management should require this and conduct inspections. Livestock trailers, a link in the food safety chain, are carriers of pathogens.