FOOD MICROBIOLOGY Food Microbiology 22 (2005) 439–447 Effects of experimental chlorate preparations as feed and water supplements on Escherichia coli colonization and contamination of beef cattle and carcasses Robin C. Anderson a,Ã , Mandy A. Carr b , Rhonda K. Miller c , David A. King c , Gordon E. Carstens c , Kenneth J. Genovese a , Todd R. Callaway a , Thomas S. Edrington a , Yong Soo Jung a , Jack L. McReynolds a , Micheal E. Hume a , Ross C. Beier a , Robert O. Elder a,1 , David J. Nisbet a a USDA/ARS, Southern Plains Agricultural Research Center, Food and Feed Safety Research Unit, 2881 F&B Road, College Station, Texas 77845, USA b Department of Agriculture, Angelo State University, Box 10888 ASU Station, San Angelo, Texas 76909, USA c Department of Animal Science, Texas A&M University, College Station, Texas 77843, USA Received 14 April 2004; accepted 8 September 2004 Abstract The effects of feed or water administration of experimental chlorate preparations on recovery of generic Escherichia coli and E. coli O157:H7 from the gut, hide and carcasses of feedlot cattle were tested. Sixty-four naturally colonized cattle were randomly assigned to one of four feed treatments with or without a 12h chlorate-containing water treatment. An analysis of variance revealed a main effect of feed treatment (P ¼ 0:002) on generic E. coli concentrations in feces collected before shipment to slaughter. Main effect means were 5.57, 4.75, 5.00 and 4.08log 10 cfu/g for animals fed an experimental chlorate product at 0, 0.01% in last meal, 0.01% for last 5 d and 0.05% of body weight in last meal, respectively. A main effect of feed treatment was observed (P ¼ 0:041) on generic E. coli concentrations in feces collected at slaughter (means for the respective treatments were 4.92, 3.57, 3.98 and 3.20log 10 cfu/g) as well as on numbers of generic E. coli recovered (P ¼ 0:034) from hide swabs collected at the rump (means for the respective treatments were 4.86, 3.92, 3.87 and 4.06 log 10 cfu/swab). A main effect of water treatment was observed (Po0:016) on generic E. coli concentrations in rumen contents (3.44 vs. 2.72cfulog 10 cfu/g for animals administered 0 or 2500 ppm active chlorate ion, respectively). Logistic regression analysis revealed a main effect of feed treatment (Po0:001) on the incidence of E. coli O157:H7 recovered from feces collected at slaughter (75%, 33%, 20% and 25% for animals fed an experimental chlorate product at 0%, 0.01% in last meal, 0.01% for last 5d and 0.05% of body weight in last meal, respectively). Animals exhibited no symptoms of chlorate toxicity and negative effects on feed or water intake or animal performance were not observed. r 2004 Elsevier Ltd. All rights reserved. Keywords: Beef cattle; Escherichia coli; Experimental chlorate product; Feed additive; Water additive 1. Introduction Enterohemorrhagic Escherichia coli strains such as E. coli O157:H7 are important foodborne pathogens. In the United States, an estimated 73,000 human infections caused by E. coli O157:H7 occur each year (Mead et al., 1999). Cattle are an important reservoir of E. coli ARTICLE IN PRESS www.elsevier.com/locate/yfmic 0740-0020/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.fm.2004.09.002 Ã Corresponding author. Tel.: +19792609317; fax: +19792609332. E-mail addresses: anderson@ffsru.tamu.edu (R.C. Anderson), rob_elder@seaboardpork.com (R.O. Elder). 1 Present address: Seaboard Farms 2700 N.E. 28th Street Guymon, Oklahoma 73942, USA.