Submitted to: Letters in Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2005
Publication Date: 5/17/2006
Citation: Looper, M.L., Edrington, T.S., Flores, R., Rosenkrans, Jr, C.F., Nihsen, M.E., Aiken, G.E. 2006. Prevalence of Escherichia coli O157:H7 and salmonella in beef steers grazing different forage diets. Letters in Applied Microbiology. 42:583-588. Interpretive Summary: E. coli and Salmonella cause foodborne illnesses in humans and thus there is great interest to reduce the occurrence of these pathogens in food products. Cattle that shed E. coli and/or salmonella in their feces can be a source of pathogenic bacteria to infect other animals and/or food products; however, factors that affect shedding are poorly understood. ARS scientists from Booneville, AR; Lexington, KY; and College Station, TX as well as the University of Arkansas compared bacteria shedding in cattle grazing tall fescue infected with wild-type or novel endophyte. Fecal shedding of either pathogenic bacteria was not affected by grazing tall fescue; however, feeding hay to grazing cattle reduced E. coli shedding and treatment with fenbendazole decreased Salmonella shedding. These results suggest common management practices can influence fecal shedding of pathogenic bacteria, and this information is important to livestock producers and extension personnel.
Technical Abstract: Beef steers (n = 98) were utilized to determine the prevalence of faecal shedding of E. coli O157:H7 and Salmonella in growing cattle grazing various forages, specifically endophyte-infected tall fescue. In Exp. I, faecal samples were collected at d 1, 64 and 95 from crossbred (< 1/4 Bos indicus), yearling steers (initial BW = 260 ± 4 kg) grazing either endophyte-infected tall fescue (E+; n = 36) or common bermudagrass paddocks (CB; n = 32). On d 85, steers grazing E+ paddocks were confined to a dry-lot pen and fed CB hay ad libitum for 10 d. Faecal samples were collected at the end of the dry-lot phase (d 95). In Exp. II, faecal samples were collected twice from crossbred Angus steers (n = 30; initial BW = 314 ± 4 kg) grazing novel endophyte-infected (NE) tall fescue or E+ tall fescue for 63 d. Within forage type, steers were treated with either ivermectin (I) or fenbendazole (F). No steers shed Salmonella during Exp. I. Further, no steers shed E. coli at d 1. More steers grazing CB (22%) were shedding E. coli than E+ steers fed CB hay (0%) at d 95 (P < 0.01). Average daily gain was not affected (P > 0.10) by E. coli shedding. In Exp. II, faecal shedding of E. coli was not influenced (P > 0.10) by forage or anthelmintic treatment. Forage type did not affect (P > 0.10) faecal shedding of Salmonella in steers. More I-treated steers (92%) were shedding Salmonella than F-treated steers (60%) at d 42. Average daily gain was similar (P > 0.10) in steers independent of Salmonella shedding. Faecal shedding of pathogenic bacteria was not affected by E+ tall fescue; however, feeding ay to grazing cattle and type of anthelmintic treatment may influence faecal shedding of pathogenic bacteria.