In "Putting E. coli and science in perspective," (BEEF, November 1998, page 11), we discussed a research study published by Cornell University that stirred up the whole country.
Specifically, the researchers drew the conclusion that problems with E. coli O157:H7 could be eliminated by feeding hay three days before slaughter. What was odd was that the Cornell researchers drew (and heavily publicized) this conclusion, even though they didn't encounter E. coli O157:H7 in any of the cattle used in the experiment.
They based their statements on a theory. The theory was that the acid rumen fluid created by high-grain diets conditions E. coli and makes them better able to withstand acid conditions further down in the digestion tract. In other words, conditions them to inhabit ruminants.
This is important, as not all enteric pathogens inhabit all species. Some, such as salmonella, are species specific. Some inhabit primarily poultry; others cattle; and some humans. (We will come back to this later.) Cornell's theory was that high-grain rations adapt E. coli O157:H7 to feedlot cattle.
Skepticism Is In Order One would have to be skeptical of the Cornell theory. Given the fact that while rumen fluid from a grain ration is acid, it is roughly 1,000 times less acid than acid from the true stomach (abomasum).
Likewise, one should be cautious about the cattle management conclusion, since a hay diet creates a much greater volume of manure. Cattle on hay diets defecate much more frequently, and the manure is much less viscous.
Crowding cattle on a hay diet together results in a much greater problem of manure stained hides. This is important as packers will tell you that most bacterial problems are caused by contaminated hides (when the hide is stripped off).
Recently, the University of Idaho completed another E. coli study - with a totally different outcome. Most noteworthy about this latest study is that the researchers actually worked with O157:H7.
In this case, they actually inoculated the cattle with the bacteria. Specifically, they placed E. coli O157:H7 directly into the rumen of steers on either a high-grain feedlot ration or a hay ration.
The results encountered in this real-life trial were totally different than the conclusions and recommendations based on the Cornell theory. The Idaho researchers discovered that hay feeding did not eliminate the shedding of E. coli O157:H7. Quite the contrary, they found cattle on a hay ration did in fact shed O157:H7; and shed them for a much longer period than cattle on a feedlot ration.
The Idaho study has been published by the Society for Microbiology*, and the primary focus of the narrative is on the advisability of feeding hay. The paper directly contradicts and refutes the Cornell recommendation. Given the potential problems associated with hay feeding, certainly this is where the focus should be.
Bacteria Did Not Colonize But there is another aspect of the Idaho study that is extremely interesting. After inoculation, while cattle on hay diets shed E. coli O157:H7 much longer than cattle on feedlot rations (40 days vs. only four days), the infection appeared transient. That is, E. coli O157:H7 apparently did not colonize and become an endemic part of the digestive tract microflora.
This refutes another tenet of the Cornell paper. In the Cornell article published in Science magazine, reference is made to the fact that vegetables are commonly contaminated with E. coli O157:H7. The paper further comments that vegetables are often fertilized with cattle manure, intimating that cattle are the primary source of E. coli O157:H7.
If it is in fact true that E. coli O157:H7 pass transiently through cattle (and do not colonize), this means that cattle are not the primary source of infection. It also means that much greater emphasis needs to be placed on the human element in food handling (since humans are known to be potential carriers).
Sanitation among farm workers is a known risk factor for fruits and vegetables. And, it may be that more scrutiny needs to be given to meat cutters and food handlers with respect to hamburger.
After the initial publication in Science, Cornell sent press releases to the major print and broadcast media outlets. The media readily snapped it up and gave publicity to what was a preliminary and unproven theory. It will be interesting to see if those same outlets publicize this much more complete (but less sensational) research.
*"Effect of Cattle Diet on E. coli O157:H7 Acid Resistance;" Carolyn Hovde, Paula Austin, Karen Cloud, C. J. Willimas and C.W. Hunt; Journal of Applied Environmental Biology; vol. 65; pages 3233-3235; 1999.
LCI Restructures The Livestock Conservation Institute has changed its name to the National Institute For Animal Agriculture Inc., effective Dec. 31, 1999. In addition, members of the 83-year-old organization voted to pare its board from 48 down to no more than 20.
The Institute is an organization of 175 national and state industry groups as well as federal and state agencies. It addresses such issues as animal health and international trade, emergency management, food safety, livestock handling, identification, emerging diseases, animal biotechnology and environmental concerns.
The Institute, based in Bowling Green, KY, can be reached at 270/782-9798 or on the Internet at www.lcionline.org/.