Influence of processed grains on fecal pH, starch concentration, and shedding of Escherichia coli O157 in feedlot cattle

¹ Department of Animal Sciences and Industry, Kansas State University, Manhattan 66505
² Department of Diagnostic Medicine and Pathobiology, Kansas State University, Manhattan 66505
³ Department of Clinical Epidemiology and Biostatistics, Health Sciences Center, McMaster University, Hamilton, Ontario, Canada L8N 3Z5

^* To whom correspondence should be addressed. E-mail: jdrouill{at}ksu.edu.

	Abstract

Manipulation of cattle diets has been proposed as a possible pre-harvest control measure for Escherichia coli O157. Altering hindgut fermentation through diet changes may be a means to reduce fecal shedding of E. coli O157. In Exp. 1, the objective was to determine whether fecal shedding of E. coli O157 was related to fecal starch concentration. Starting on d 20, and every wk thereafter until d 61, steers in 54 pens (6 to 7 steers per pen) were sampled (n = 122) using feces and by rectoanal mucosal swabs (RAMS) for E. coli O157 and fecal starch concentration determinations. Escherichia coli O157 prevalence was 3.3% in fecal samples, 4.1% as measured by RAMS, and 4.9% by fecal or RAMS samples. Steers positive for E. coli O157 contained 21% more (P < 0.05) fecal starch than steers that were negative for E. coli O157. In Exp. 2, we attempted to alter the concentration of starch escaping rumen fermentation by feeding finishing diets based on steam-flaked corn (SFC) and dry-rolled corn (DRC) to 30 heifers prescreened for being culture positive for fecal E. coli O157. Starting on d 13, heifers were sampled (feces and RAMS) weekly to monitor fecal pH and fecal starch concentration, and prevalence of E. coli O157. Prevalence of E. coli O157 remained above 30% for the first 13 d and then declined (P < 0.05) over the entire 7-wk period. Based on RAMS prevalence of E. coli O157 tended to be greater (P = 0.08) for heifers fed SFC than DRC diet. After d 20, heifers fed DRC had greater (P < 0.05) fecal starch and lower (P < 0.05) fecal pH than heifers fed SFC. Fecal pH was negatively correlated (r = -0.34; P < 0.05; n = 143) with fecal starch concentration. Fecal starch concentration and pH were not different (P > 0.05) for heifers positive or negative for E. coli O157. Our data suggest that fecal shedding of E. coli O157 was not related to fecal pH or starch concentration in cattle fed grain-based diets.

Key Words: Escherichia coli O157, grain processing, fecal starch, feedlot dattle