Q At the Meat Animal Research Center (MARC), William Laegried, DVM, showed a reduction in E. coli O157:H7 shedding from 52% to 18% for cattle on hay only rations at the end of seven days. (See September BEEF, page 54.) What is the significance of this study compared to the Idaho study? Wouldn't it appear the economic and health drawbacks from Laegried's study weigh heavily against hay feeding?
Steve Helyesen North Dakota
A It is difficult to discuss William Laegried's study since it has not yet been published. In a telephone conversation, Laegried said the health problems became so acute they had to terminate the hay feeding.
Regardless, E. coli O157:H7 is an issue we must address in whatever way possible, and we should not rule anything out. The real question is, "Does hay feeding work?" One thing for certain is that the early media speculation that three days of hay feeding could eliminate shedding is wrong. In the MARC study, they went seven days and still had substantial shedding.
A University of Idaho study conducted by microbiologist Caroline Bohach reported hay feeding actually increased shedding. Why the contrast? I don't know. Indeed, this is an issue that sharply divides various research groups.
The Fundamental Issue Due to the media coverage, hay feeding has been the focal point, but there is a far more fundamental question that may hold the answer. Unfortunately, there's total disagreement between researchers in this area.
There are researchers who believe ruminants are the natural host of E. coli O157:H7. Others, such as Bohach, believe E. coli O157:H7 is an environmental organism - an organism that can survive and replicate outside of the animal.
Dale Hancock, a veterinary epidemiologist with Washington State University, has found E. coli O157:H7 in a broad array of feeds. Most important, Hancock has found that O157 can readily replicate in feeds (when moisture content is above 25%).
Hancock also routinely finds O157 in water, and believes water is the primary route of infection (more later). He also found O157 in a number of species: deer, horses, dogs and birds. That's in addition to sheep, dairy cattle and beef cattle.
In his intensive studies of cattle, Hancock found that infections normally last about 60 days. What I find highly important is that he says he has not identified cattle that are persistent carriers. They acquire O157, which passes through as a transient infection.
Hancock finds the number of cattle testing positive usually triples during summer. This is consistent with his theory that water is the primary source of infection. During summer, water consumption increases, thereby increasing the intake of infective cells.
Published MARC research has shown a percentage of calves on most ranches to be infected. Meanwhile, others that are negative have antibody titers for O157. This would be consistent with Hancock's transient infection theory.
The University of Idaho's Bohach also subscribes to the transient infection theory. In a previous study, she infected sheep and then serially slaughtered them over time. In examining the digestive tracts she found no particular site where E. coli O157:H7 colonized. As time increased, O157 tended to be found farther down the digestive tract.
What About Hay Vs. Grain? In the opinions of several researchers (but by no means all), the type of ration probably doesn't mean much. More important would be the E. coli O157:H7 content of the ration (or water supply). Cattle become infected and over time the infection dissipates.
Hay, which is dry, would not allow E. coli to replicate, and therefore would be much less likely to infect or re-infect. The popping or micronizing of grains would certainly kill any E. coli present, as would steam flaking. However, the moisture added by steam flaking would allow E. coli to grow if another feed were added to a ration that contained E. coli.
Hancock has found O157 in barley. Tempering (soaking in water) is a common practice with barley, and would clearly be contraindicated as far as E. coli is concerned.
Epidemiologically, there is evidence that type of ration is not necessarily a factor. As mentioned, MARC has identified ranch calves positive with O157. Likewise, Hancock has found an equal number of positives in dairy cattle on forage rations as well as range cows. A Canadian researcher, Joyce Vandonkersgoed, has likewise reported O157 positives in cull range cows at equal or greater levels than cows on grain rations.
Bottom Line There is very little known for certain but it appears to me Bohach's theory that O157 is an environmental bacteria is most likely correct. The question is how to reduce the infection rate in farm animals? Hancock believes that chlorinating water systems can reduce but not eliminate infection rates. Bohach is working on a vaccine.
Ultimately, the public must realize that ground meat must be thoroughly cooked - just as pork must be thoroughly cooked to prevent Trichina and egg yolks must be cooked hard to prevent Salmonella poisoning. Animal and Plant Health Inspection Service veterinarians will privately tell you that short of irradiation, there is no way to guarantee ground meat does not contain pathogenic bacteria.