Feeding cattle hay instead of grain five days before slaughter may reduce the danger from food-borne bacteria, say USDA-ARS and Cornell University mi-crobiologists.

Hay rids the animal's digestive tract of E. coli bacteria that have developed resistance to strong acids, say the researchers.

"Most bacteria are killed by the acid of stomach juice, but E. coli from grain-fed cattle are resistant to strong acids," explains microbiologist James Russell. "When people eat foods contaminated with acid-resistant E. coli - including pathogenic strains like O157:H7 - the chance of getting sick increases."

E. coli is a normal bacterium in the gastrointestinal tract of animals and humans, and most types aren't harmful. But disease-carrying strains like E. coli O157:H7 produce toxins that cause bloody diarrhea or even kidney failure in humans. About 20,000 E. coli cases and 200 deaths are reported annually.

Because the bovine digestive tract digests starch poorly, some undigested grain reaches the colon, where it ferments. When the grain ferments, acids accumulate, and a large portion of the E. coli produced are acid-resistant, Russell explains.

Grain doesn't promote the growth of E. coli, but it increases the chance that the acid-resistant type will develop.

"Hay doesn't promote either the growth or acid resistance of E. coli," says Russell. "When we switched cattle from grain-based diets to hay for only five days, acid-resistant E. coli could no longer be detected."

In the study, beef cattle fed grain-based rations typical of commercial feedlots had 1 million acid-resistant E. coli per gram of feces. By comparison, cattle fed hay had only acid-sensitive E. coli, and those bacteria were destroyed by an acid shock that mimics the human stomach.

A brief period of hay feeding before slaughter should not affect carcass size or meat quality. The diet change could be implemented with minimal expense and inconvenience to feedlot operators, says Donald Beermann, a Cornell animal scientist.