In 2008, I explored in an op-ed the popular belief that switching from grain to grass feeding could be the solution to the problem with E. coli O157:H7 in beef cattle. Flashing forward six years, are we any closer to finding the Holy Grail for on-farm food safety through the diets we feed cattle?
To answer this question, more than another 20 additional pieces of literature were reviewed and are summarized below. The goal in doing this literature review is to help better inform grass-fed producers and consumers about the risks from E. coli O157 whether eating grass-fed or grain-fed beef products.
This piece is not meant to stifle innovation in farming and alternative food markets, or deny positive evidence-based nutritional claims about grass-fed beef. But, it is critically important that food producers, as well as journalists, chefs, and others promoting grass-fed beef, recognize that they have a shared responsibility to provide consumers with accurate information about the safety of beef products. People working in these high profile professions are not expected to understand all of the science, but they should do some honest research and talk to experts in the field before incorrectly downplaying to consumers the risk of E. coli O157:H7 from grass-fed beef.
In a 2010 Slate article (Beware the Myth of Grass-Fed Beef), James E. McWilliams, author of Just Food: Where Locavores Get It Wrong and How We Can Truly Eat Responsibly and a professor of history at Texas State University, wrote on the grass-fed vs grain fed literature. He calls-out a Chef for possibly putting the public at risk by ignoring the science behind food safety and grass-fed beef. Toward the end of the article he says:
“The point in dredging up these studies—ones the media never covered—is not to play gotcha with advocates of grass-fed beef. (As mentioned above, grass-fed beef may be healthier than conventional beef over all, and kinder to the animals.) Instead, it’s a warning that advocacy for a trendy food choice might result in a public health hazard. Such a fear is confirmed by consulting the cooking directions provided by many purveyors of grass-fed beef. The home page for one major producer explains that “cooking ‘real food’ is not the same as cooking concocted food. … Grass-fed meats are best when raw (steak tartar), rare, or medium rare.”
Mr. McWilliam’s virtually portends an outbreak from grass-fed beef.
In 2014, at least 3 case-patients have developed E. coli O157:H7 infections (including one HUS and death) linked to grass-fed beef sold at Whole Foods and produced by Rain Crow Ranch, http://www.raincrowranch.com/ also home of the American Grassfed Association (AGA). Patricia Whisnant, Rain Crow Ranch Co-Founder and President of AGA, was quoted on a food blog:
“When that animal, that ruminant, that cow, is fed on grass and maintains a healthy ruminant as it’s supposed to at a neutral pH, then if that E. Coli goes through and for some reason contaminates the finished beef, and is consume by a human, that pathogen is immediately killed by the acid environment of the human stomach.”
Tragically, misinformation about the safety of grass-fed beef and E. coli O157:H7 could lead to a false sense of security among producers, buyers, and consumers, ultimately resulting in illnesses and even death from eating grass-fed beef.
This is what the science actually tells us at this time about grass-fed vs grain-fed beef safety.
- Cattle are considered the primary hosts of E. coli O157:H7. The organism has been isolated repeatedly from cattle, and implicated as the root cause of outbreaks from beef and dairy products. For this reason, identification of on-farm management practices that would reduce E. coli O157:H7 in cattle reservoirs is an active area of research. Diet has been investigated extensively as a possible pre-harvest intervention, but the research remains inconclusive.
- In 1998, a study published by Cornell University excited the science and popular media worlds. The researchers suggested that cattle could be fed hay for a brief period before slaughter to significantly reduce the risk of foodborne E. coli infection. They based this conclusion on a hypothesis that grain feeding increases acid resistance of E. coli in cattle. Although they showed increased acid resistance in E. coli from grain-fed cattle, only 3 animals were studied (small sample size), and they used “generic” E. coli stains, not pathogenic E. coli O157:H7.
- The “acid” theory was subsequently debunked in follow-up studies, but has continued as perhaps the most pervasive food safety myth ever. Dietary influences on E. coli O157:H7 shedding and concentration continue to be important areas of pre-harvest food safety research, but recent findings indicate the situation is far more complex and nuanced than the original simplified theory proposed in the widely cited 1998 Science paper.
- Areas of current research into the role of diet and E. coli O157:H7 in cattle include examination of the influence of distiller’s and brewer’s grains, and different combinations of forage and grains. Intriguing new research shows that the gut ecosystem may play more of a role than the original acid resistance hypotheses.
- In summary, the scientific evidence at this time still does not support a broad conclusion that grass feeding significantly and consistently reduces the risk of E. coli O157:H7 or other dangerous foodborne pathogens entering the food chain. Consumers should continue to follow recommendations for safe handling and cooking of beef products regardless of whether they are grass-fed or grain-fed.
1. Bach, S. J., L. J. Selinger, K. Stanford, and T. A. McAllister. 2005. Effect of supplementing corn- or barley-based feedlot diets with canola oil on faecal shedding of Escherichia coli O157:H7 by steers. J Appl Microbiol 98:464-475.
3. Bailey, G. D., B. A. Vanselow, M. A. Hornitzky, S. I. Hum, G. J. Eamens, P. A. Gill, K. H. Walker, and J. P. Cronin. 2003. A study of the foodborne pathogens: Campylobacter, Listeria and Yersinia, in faeces from slaughter-age cattle and sheep in Australia. Commun Dis Intell Q Rep 27:249-257.
4. Berg, J., T. McAllister, S. Bach, R. Stilborn, D. Hancock, and J. LeJeune. 2004. Escherichia coli O157:H7 excretion by commercial feedlot cattle fed either barley- or corn-based finishing diets. J Food Prot 67:666-671.
5. Brownlie, L. E., and F. H. Grau. 1967. Effect of food intake on growth and survival of salmonellas and Escherichia coli in the bovine rumen. J Gen Microbiol 46:125-134.
6. Buchko, S. J., R. A. Holley, W. O. Olson, V. P. Gannon, and D. M. Veira. 2000. The effect of different grain diets on fecal shedding of Escherichia coli O157:H7 by steers. J Food Prot 63:1467-1474.
7. Callaway, T. R., M. A. Carr, T. S. Edrington, R. C. Anderson, and D. J. Nisbet. 2009. Diet, Escherichia coli O157:H7, and cattle: a review after 10 years. Curr Issues Mol Biol 11:67-79.
8. Callaway, T. R., R. O. Elder, J. E. Keen, R. C. Anderson, and D. J. Nisbet. 2003. Forage feeding to reduce preharvest Escherichia coli populations in cattle, a review. J Dairy Sci 86:852-860.
9. Cray, W. C., Jr., T. A. Casey, B. T. Bosworth, and M. A. Rasmussen. 1998. Effect of dietary stress on fecal shedding of Escherichia coli O157:H7 in calves. Appl Environ Microbiol 64:1975-1979.
10. Daley, C. A., A. Abbott, P. S. Doyle, G. A. Nader, and S. Larson. 2010. A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef. Nutr J 9:10.
11. de Jonge, R., K. Takumi, W. S. Ritmeester, and F. M. van Leusden. 2003. The adaptive response of Escherichia coli O157 in an environment with changing pH. J Appl Microbiol 94:555-560.
12. Depenbusch, B. E., T. G. Nagaraja, J. M. Sargeant, J. S. Drouillard, E. R. Loe, and M. E. Corrigan. 2008. Influence of processed grains on fecal pH, starch concentration, and shedding of Escherichia coli O157 in feedlot cattle. J Anim Sci 86:632-639.
13. Dewell, G. A., J. R. Ransom, R. D. Dewell, K. McCurdy, I. A. Gardner, A. E. Hill, J. N. Sofos, K. E. Belk, G. C. Smith, and M. D. Salman. 2005. Prevalence of and risk factors for Escherichia coli O157 in market-ready beef cattle from 12 U.S. feedlots. Foodborne Pathog Dis 2:70-76.
14. Diez-Gonzalez, F., T. R. Callaway, M. G. Kizoulis, and J. B. Russell. 1998. Grain feeding and the dissemination of acid-resistant Escherichia coli from cattle. Science 281:1666-1668.
15. Djordjevic, S. P., V. Ramachandran, K. A. Bettelheim, B. A. Vanselow, P. Holst, G. Bailey, and M. A. Hornitzky. 2004. Serotypes and virulence gene profiles of shiga toxin-producing Escherichia coli strains isolated from feces of pasture-fed and lot-fed sheep. Appl Environ Microbiol 70:3910-3917.
16. Doyle, M. P., and M. C. Erickson. 2006. Reducing the carriage of foodborne pathogens in livestock and poultry. Poult Sci 85:960-973.
17. Edrington, T. S., J. C. MacDonald, R. L. Farrow, T. R. Callaway, R. C. Anderson, and D. J. Nisbet. 2010. Influence of wet distiller’s grains on prevalence of Escherichia coli O157:H7 and Salmonella in feedlot cattle and antimicrobial susceptibility of generic Escherichia coli isolates. Foodborne Pathog Dis 7:605-608.
18. Fegan, N., P. Vanderlinde, G. Higgs, and P. Desmarchelier. 2004. The prevalence and concentration of Escherichia coli O157 in faeces of cattle from different production systems at slaughter. J Appl Microbiol 97:362-370.
19. Fox, J. T., B. E. Depenbusch, J. S. Drouillard, and T. G. Nagaraja. 2007. Dry-rolled or steam-flaked grain-based diets and fecal shedding of Escherichia coli O157 in feedlot cattle. J Anim Sci 85:1207-1212.
20. Franz, E., A. D. van Diepeningen, O. J. de Vos, and A. H. van Bruggen. 2005. Effects of cattle feeding regimen and soil management type on the fate of Escherichia coli O157:H7 and salmonella enterica serovar typhimurium in manure, manure-amended soil, and lettuce. Appl Environ Microbiol 71:6165-6174.
21. Fu, C. J., J. H. Porter, E. E. Felton, J. W. Lehmkuhler, and M. S. Kerley. 2003. Pre-harvest factors influencing the acid resistance of Escherichia coli and E. coli O157:H7. J Anim Sci 81:1080-1087.
22. Garber, L. P., S. J. Wells, D. D. Hancock, M. P. Doyle, J. Tuttle, J. A. Shere, and T. Zhao. 1995. Risk factors for fecal shedding of Escherichia coli O157:H7 in dairy calves. J Am Vet Med Assoc 207:46-49.
23. Gilbert, R. A., S. E. Denman, J. Padmanabha, N. Fegan, D. Al Ajmi, and C. S. McSweeney. 2008. Effect of diet on the concentration of complex Shiga toxin-producing Escherichia coli and EHEC virulence genes in bovine faeces, hide and carcass. Int J Food Microbiol 121:208-216.
24. Gilbert, R. A., N. Tomkins, J. Padmanabha, J. M. Gough, D. O. Krause, and C. S. McSweeney. 2005. Effect of finishing diets on Escherichia coli populations and prevalence of enterohaemorrhagic E. coli virulence genes in cattle faeces. J Appl Microbiol 99:885-894.
25. Grauke, L. J., S. A. Wynia, H. Q. Sheng, J. W. Yoon, C. J. Williams, C. W. Hunt, and C. J. Hovde. 2003. Acid resistance of Escherichia coli O157:H7 from the gastrointestinal tract of cattle fed hay or grain. Vet Microbiol 95:211-225.
26. Hancock, D. D., T. E. Besser, C. Gill, and C. H. Bohach. 1999. Cattle, hay and E. coli. Science 284:51-53.
27. Harmon, B. G., C. A. Brown, S. Tkalcic, P. O. Mueller, A. Parks, A. V. Jain, T. Zhao, and M. P. Doyle. 1999. Fecal shedding and rumen growth of Escherichia coli O157:H7 in fasted calves. J Food Prot 62:574-579.
28. Herriott, D. E., D. D. Hancock, E. D. Ebel, L. V. Carpenter, D. H. Rice, and T. E. Besser. 1998. Association of herd management factors with colonization of dairy cattle by Shiga toxin-positive Escherichia coli O157. J Food Prot 61:802-807.
29. Hovde, C. J., P. R. Austin, K. A. Cloud, C. J. Williams, and C. W. Hunt. 1999. Effect of cattle diet on Escherichia coli O157:H7 acid resistance. Appl Environ Microbiol 65:3233-3235.
30. Hussein, H. S. 2007. Prevalence and pathogenicity of Shiga toxin-producing Escherichia coli in beef cattle and their products. J Anim Sci 85:E63-72.
31. Jacob, M. E., T. R. Callaway, and T. G. Nagaraja. 2009. Dietary interactions and interventions affecting Escherichia coli O157 colonization and shedding in cattle. Foodborne Pathog Dis 6:785-792.
32. Jacob, M. E., J. T. Fox, J. S. Drouillard, D. G. Renter, and T. G. Nagaraja. 2008. Effects of dried distillers’ grain on fecal prevalence and growth of Escherichia coli O157 in batch culture fermentations from cattle. Appl Environ Microbiol 74:38-43.
33. Jacob, M. E., J. T. Fox, J. S. Drouillard, D. G. Renter, and T. G. Nagaraja. 2009. Evaluation of feeding dried distiller’s grains with solubles and dry-rolled corn on the fecal prevalence of Escherichia coli O157:H7 and Salmonella spp. in cattle. Foodborne Pathog Dis 6:145-153.
34. Jacob, M. E., J. T. Fox, S. K. Narayanan, J. S. Drouillard, D. G. Renter, and T. G. Nagaraja. 2008. Effects of feeding wet corn distillers grains with solubles with or without monensin and tylosin on the prevalence and antimicrobial susceptibilities of fecal foodborne pathogenic and commensal bacteria in feedlot cattle. J Anim Sci 86:1182-1190.
35. Jacob, M. E., Z. D. Paddock, D. G. Renter, K. F. Lechtenberg, and T. G. Nagaraja. 2010. Inclusion of dried or wet distillers’ grains at different levels in diets of feedlot cattle affects fecal shedding of Escherichia coli O157:H7. Appl Environ Microbiol 76:7238-7242.
36. Jacob, M. E., G. L. Parsons, M. K. Shelor, J. T. Fox, J. S. Drouillard, D. U. Thomson, D. G. Renter, and T. G. Nagaraja. 2008. Feeding supplemental dried distiller’s grains increases faecal shedding of Escherichia coli O157 in experimentally inoculated calves. Zoonoses Public Health 55:125-132.
37. Jay, M. T., M. Cooley, D. Carychao, G. W. Wiscomb, R. A. Sweitzer, L. Crawford-Miksza, J. A. Farrar, D. K. Lau, J. O’Connell, A. Millington, R. V. Asmundson, E. R. Atwill, and R. E. Mandrell. 2007. Escherichia coli O157:H7 in feral swine near spinach fields and cattle, central California coast. Emerg Infect Dis 13:1908-1911.
38. Krause, D. O., W. J. Smith, L. L. Conlan, J. M. Gough, M. A. Williamson, and C. S. McSweeney. 2003. Diet influences the ecology of lactic acid bacteria and Escherichia coli along the digestive tract of cattle: neural networks and 16S rDNA. Microbiology 149:57-65.
39. Krueger, N. A., R. C. Anderson, W. K. Krueger, W. J. Horne, I. V. Wesley, T. R. Callaway, T. S. Edrington, G. E. Carstens, R. B. Harvey, and D. J. Nisbet. 2008. Prevalence and concentration of Campylobacter in rumen contents and feces in pasture and feedlot-fed cattle. Foodborne Pathog Dis 5:571-577.
40. Kudva, I. T., P. G. Hatfield, and C. J. Hovde. 1995. Effect of diet on the shedding of Escherichia coli O157:H7 in a sheep model. Appl Environ Microbiol 61:1363-1370.
41. Kuhnert, P., C. R. Dubosson, M. Roesch, E. Homfeld, M. G. Doherr, and J. W. Blum. 2005. Prevalence and risk-factor analysis of Shiga toxigenic Escherichia coli in faecal samples of organically and conventionally farmed dairy cattle. Vet Microbiol 109:37-45.
42. Leheska, J. M., L. D. Thompson, J. C. Howe, E. Hentges, J. Boyce, J. C. Brooks, B. Shriver, L. Hoover, and M. F. Miller. 2008. Effects of conventional and grass-feeding systems on the nutrient composition of beef. J Anim Sci 86:3575-3585.
43. Looper, M. L., T. S. Edrington, R. Flores, J. M. Burke, T. R. Callaway, G. E. Aiken, F. N. Schrick, and C. F. Rosenkrans, Jr. 2007. Influence of dietary endophyte (Neotyphodium coenophialum)-infected tall fescue (Festuca arundinacea) seed on fecal shedding of antibiotic resistance-selected Escherichia coli O157:H7 in ewes. J Anim Sci 85:1102-1108.
44. Looper, M. L., T. S. Edrington, R. Flores, C. F. Rosenkrans, Jr., M. E. Nihsen, and G. E. Aiken. 2006. Prevalence of Escherichia coli O157:H7 and Salmonella in beef steers consuming different forage diets. Lett Appl Microbiol 42:583-588.
45. Looper, M. L., T. S. Edrington, and C. F. Rosenkrans, Jr. 2009. Influence of body condition and forage type on prevalence of Escherichia coli O157:H7 and Salmonella in grazing beef cows. Lett Appl Microbiol 49:361-365.
46. Lowe, R. M., K. Munns, L. B. Selinger, L. Kremenik, D. Baines, T. A. McAllister, and R. Sharma. 2010. Factors influencing the persistence of Escherichia coli O157:H7 lineages in feces from cattle fed grain versus grass hay diets. Can J Microbiol 56:667-675.
47. Oliver, S. P., D. A. Patel, T. R. Callaway, and M. E. Torrence. 2009. ASAS Centennial Paper: Developments and future outlook for preharvest food safety. J Anim Sci 87:419-437.
48. Paddock, Z. D., D. G. Renter, X. Shi, C. R. Krehbiel, B. DeBey, and T. G. Nagaraja. 2013. Effects of feeding dried distillers grains with supplemental starch on fecal shedding of Escherichia coli O157:H7 in experimentally inoculated steers. J Anim Sci 91:1362-1370.
49. Peterson, R. E., T. J. Klopfenstein, R. A. Moxley, G. E. Erickson, S. Hinkley, G. Bretschneider, E. M. Berberov, D. Rogan, and D. R. Smith. 2007. Effect of a vaccine product containing type III secreted proteins on the probability of Escherichia coli O157:H7 fecal shedding and mucosal colonization in feedlot cattle. J Food Prot 70:2568-2577.
50. Reinstein, S., J. T. Fox, X. Shi, M. J. Alam, D. G. Renter, and T. G. Nagaraja. 2009. Prevalence of Escherichia coli O157:H7 in organically and naturally raised beef cattle. Appl Environ Microbiol 75:5421-5423.
51. Renter, D. G., J. M. Sargeant, and L. L. Hungerford. 2004. Distribution of Escherichia coli O157:H7 within and among cattle operations in pasture-based agricultural areas. Am J Vet Res 65:1367-1376.
52. Renter, D. G., J. M. Sargeant, R. D. Oberst, and M. Samadpour. 2003. Diversity, frequency, and persistence of Escherichia coli O157 strains from range cattle environments. Appl Environ Microbiol 69:542-547.
53. Russell, J. B., F. Diez-Gonzalez, and G. N. Jarvis. 2000. Invited review: effects of diet shifts on Escherichia coli in cattle. J Dairy Sci 83:863-873.
54. Russell, J. B., F. Diez-Gonzalez, and G. N. Jarvis. 2000. Potential effect of cattle diets on the transmission of pathogenic Escherichia coli to humans. Microbes Infect 2:45-53.
55. Sargeant, J. M., J. R. Gillespie, R. D. Oberst, R. K. Phebus, D. R. Hyatt, L. K. Bohra, and J. C. Galland. 2000. Results of a longitudinal study of the prevalence of Escherichia coli O157:H7 on cow-calf farms. Am J Vet Res 61:1375-1379.
56. Synge, B. A., M. E. Chase-Topping, G. F. Hopkins, I. J. McKendrick, F. Thomson-Carter, D. Gray, S. M. Rusbridge, F. I. Munro, G. Foster, and G. J. Gunn. 2003. Factors influencing the shedding of verocytotoxin-producing Escherichia coli O157 by beef suckler cows. Epidemiol Infect 130:301-312.
57. Tkalcic, S., C. A. Brown, B. G. Harmon, A. V. Jain, E. P. Mueller, A. Parks, K. L. Jacobsen, S. A. Martin, T. Zhao, and M. P. Doyle. 2000. Effects of diet on rumen proliferation and fecal shedding of Escherichia coil O157:H7 in calves. J Food Prot 63:1630-1636.
58. Van Baale, M. J., J. M. Sargeant, D. P. Gnad, B. M. DeBey, K. F. Lechtenberg, and T. G. Nagaraja. 2004. Effect of forage or grain diets with or without monensin on ruminal persistence and fecal Escherichia coli O157:H7 in cattle. Appl Environ Microbiol 70:5336-5342.
59. Van Elswyk, M. E., and S. H. McNeill. 2014. Impact of grass/forage feeding versus grain finishing on beef nutrients and sensory quality: the U.S. experience. Meat Sci 96:535-540.
60. Wells, J. E., S. D. Shackelford, E. D. Berry, N. Kalchayanand, J. M. Bosilevac, and T. L. Wheeler. 2011. Impact of reducing the level of wet distillers grains fed to cattle prior to harvest on prevalence and levels of Escherichia coli O157:H7 in feces and on hides. J Food Prot 74:1611-1617.
61. Wells, J. E., S. D. Shackelford, E. D. Berry, N. Kalchayanand, M. N. Guerini, V. H. Varel, T. M. Arthur, J. M. Bosilevac, H. C. Freetly, T. L. Wheeler, C. L. Ferrell, and M. Koohmaraie. 2009. Prevalence and level of Escherichia coli O157:H7 in feces and on hides of feedlot steers fed diets with or without wet distillers grains with solubles. J Food Prot 72:1624-1633.
62. Williams, K. J., M. P. Ward, O. P. Dhungyel, and E. J. Hall. 2014. Risk factors for Escherichia coli O157 shedding and super-shedding by dairy heifers at pasture. Epidemiol Infect:1-12.
63. Yang, H. E., W. Z. Yang, J. J. McKinnon, T. W. Alexander, Y. L. Li, and T. A. McAllister. 2010. Survival of Escherichia coli O157:H7 in ruminal or fecal contents incubated with corn or wheat dried distillers’ grains with solubles. Can J Microbiol 56:890-895.
64. Zhang, J., S. K. Wall, L. Xu, and P. D. Ebner. 2010. Contamination rates and antimicrobial resistance in bacteria isolated from “grass-fed” labeled beef products. Foodborne Pathog Dis 7:1331-1336.
65. Zhao, L., P. J. Tyler, J. Starnes, C. L. Bratcher, D. Rankins, T. A. McCaskey, and L. Wang. 2013. Correlation analysis of Shiga toxin-producing Escherichia coli shedding and faecal bacterial composition in beef cattle. J Appl Microbiol 115:591-603.