Author: Jill Heemstra, Extension Educator, University of Nebraska, jheemstra@unl.edu
The recent human outbreak of E. coli 0157:H7 traced to spinach that may have links to livestock manure has reinvigorated a lively debate. There is a persistent and passionate assertion, sometimes repeated in the popular press, that E. coli 0157:H7 presence in livestock is due to the "unnatural," high-grain content in the diet of confined animals. Dale Hancock and Tom Besser of the College of Veterinary Medicine, Washington State University, conducted a literature review of research on this topic. A summary of some of the major conclusions drawn from their review follows.
- Worldwide, many researchers have documented that the prevalence of E. coli 0157:H7 in the feces of cattle on pasture or range (grass-fed) is similar to that of confined (grain-fed) cattle of similar age.
- The assertion that grain diets are the reason why E. coli 0157:H7 is found in livestock appears to originate from a research project that looked at E. coli populations as a whole, not at E. coli 0157:H7 specifically. Subsequent research has shown that E. coli 0157:H7 behaves differently from other E. coli strains.
Another aspect of the debate over this topic is the theory that E. coli 0157:H7 organisms in grain-fed animals are more acid-resistant and therefore more likely to survive through the human stomach to the intestine, where they can cause illness. Some of the points from Dr. Hancock and Dr. Besser's review:
- Research has not found differences in the acid resistance of E. coli 0157:H7 populations in the digestive tracts of animals fed hay versus those fed grain.
- The acid resistance of E. coli 0157:H7 may be less important in determining the pathogen survivability to the human intestine than previously speculated.
Overall, the balance of findings in scientific literature tends to dispute the assertion that cattle diets play a major role in exposure or infectivity of E. coli 0157:H7 to humans.
Additional reading:
Hancock, D and T Besser. 2006. E. coli O157:H7 in hay- or grain-fed cattle. College of Veterinary Medicine, Washington State University. http://www.puyallup.wsu.edu/dairy/joeharrison/publications.asp
