Submitted to: Journal of Animal Science
Publication Type: Proceedings
Publication Acceptance Date: February 21, 2002
Publication Date: January 20, 2003
Citation: CALLAWAY, T.R., ELDER, R.O., KEEN, J.E., ANDERSON, R.C., NISBET, D.J. FORAGE FEEDING TO REDUCE PRE-HARVEST E. COLI POPULATIONS IN CATTLE, A REVIEW. JOURNAL OF ANIMAL SCIENCE. 2003. V. 86. P. 852-860. Interpretive Summary: Escherichia coli is a common bacterium found in the gut of animals; however, the strain O157:H7 is a virulent food borne pathogen that is closely associated with cattle. Cattle in the U.S. are fed large amounts of grain and contain large populations of E. coli. Switching cattle from grain to hay causes a decrease in E. coli populations in the feces, but the results have been highly variable. Even though feeding hay may decrease the numbers of this pathogenic E. coli, due to economic reasons other methods for reducing E. coli in cattle still need to be explored.
Technical Abstract: E. coli are commensal organisms within the host gut, some enteropathogenic strains of E. coli can cause hemorrhagic colitis in humans. The most notable enterohemorrhagic E. coli (EHEC) strain is O157:H7. Cattle are natural reservoirs of E. coli O157:H7; and it has been reported that as many as 30% of all cattle carry this pathogen, and in some circumstances this can be as high as 80%. Feedlot and high-producing dairy cattle are fe high grain rations in order to increase feed efficiency. Because cattle have low amylase activity, much of the starch passes to the hindgut where it is fermented. EHEC are capable of fermenting sugars from starch breakdown in the colon, and populations of E. coli have been shown to be higher in grain fed cattle, and this has been correlated with E. coli O157:H7 shedding in barley fed cattle. When cattle were switched from a high grain (corn) diet to a forage diet, generic E. coli populations declined 1000-fold within 5 days and the ability of the fecal generic E. coli population to survive an acid shock similar to the human gastric stomach decreased. Other researchers have shown that a switch from grain to hay caused a smaller decrease in E. coli populations, but did not observe the same effect on gastric shock survivability. In a study with cattle naturally infected with E. coli O157:H7, fewer cattle shed E. coli O157:H7 when switched from a feedlot ration to a forage-based diet compared to cattle continuously fed a feedlot ration. Results indicate that switching cattle from grain to forage could reduce EHEC populations in cattle prior to slaughter; however, the economic impact of this needs to be examined.