Bill Marler posted some research:
Grass-Fed vs Grain-Fed Beef and the Holy Grail: A Literature Review
"E. coli O157:H7, Campylobacter, Salmonella, and other dangerous pathogens have been repeatedly isolated from both grass and grain fed livestock."He concluded:
"Studies by other researchers worldwide have since found little difference in acid resistant E. coli O157:H7 among grain- verses grass-fed cattle, and some even found more E. coli O157:H7 shed by grass-fed animals."
"Outbreaks have been traced back to grass-fed and pastured animals, as well as animals in feedlots. Notably, the E. coli O157:H7 spinach outbreak strain in 2006 was isolated from grass-fed cattle."
"Another outbreak of E. coli O157:H7 was linked recently to raw milk and colostrum from cattle raised organically on grass."
"In summary, the scientific evidence at this time does not support a broad conclusion that grass feeding significantly reduces the risk of E. coli O157:H7 or other dangerous foodborne pathogens from entering the food chain."