Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 21, 2002
Publication Date: N/A
Interpretive Summary: Escherichia coli is a common bacterium found in food animals, however the strain 0157:H7 is a virulent food borne pathogen that is commonly found in cattle. Cattle in the U.S. are fed large amounts of grain and contain large populations of E. coil. Some studies have shown that switching cattle from grain to hay can cause a decrease in E. coli populations in the feces, however other studies have shown little to no effect, suggesting results can be highly variable. In spite of the possible benefits of feeding hay, it may not be economically viable, therefore other alternatives need to be explored that can reduce E. coli populations in cattle prior to harvest.
Technical Abstract: Although E. coli are conixnensal organisms that reside 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 0157:H7. Cattle are asymptoinatic natural reservoirs of E. coli 0157:H7; and it has been reported in the literature that under some circumstances as many as 80% all cattle can be carriers of this pathogen. Feedlot and high- producing dairy cattle are fed 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 ferment sugars released 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 0157:H7 shedding in barley fed cattle. When cattle were abruptly 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, with no effect on gastric shock survivability. In a study that used cattle naturally infected with E. coli 0157:H7, fewer cattle shed E. coli 0157:H7 when switched from a feedlot ration to a forage-based diet compared to cattle continuously fed a feedlot ration. Although results differ in respect to E. coli survivability due to acid shock, substituting hay for grain has resulted in decreased E. coli shedding, but the economic impact of this strategy needs to be examined.