Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2006
Publication Date: September 1, 2006
Citation: Edrington, T.S., Looper, M.L., Duke, S.E., Callaway, T.R., Genovese, K.J., Anderson, R.C., Nisbet, D.J. 2006. Effect of ionophore supplementation on the incidence of Escherichia coli O157:H7 and Salmonella and antimicrobial susceptibility of fecal coliforms in stocker cattle. Foodborne Pathogens and Disease. 3:284-291. Interpretive Summary: Ionophores are antibiotics that improve the growth and performance of young cattle. The use of ionophores in cattle production is very common. The similar time frame in which ionophore use began and food sickness caused by E. coli O157:H7 has raised concerns. The purpose of the present study was to determine if feeding ionophore to grazing cattle for 60 days had any effect on Salmonella or E. coli O157:H7. We also examined the ability of antibiotics to kill fecal coliforms isolated from these animals fed ionophore. Results showed no effect of ionophore feeding on fecal shedding of E. coli O157:H7 or Salmonella when fed for 60 days. Furthermore, feeding ionophores had no effect on the ability of antibiotics to kill fecal coliforms.
Technical Abstract: To examine the effect of ionophore supplementation on fecal shedding of E. coli O157:H7 and Salmonella, crossbred beef calves (n = 113; mean BW 243 kg) were fed a mineral supplement with ionophore (1.76 g lasalocid/kg) for 61 d. Control calves received an identical mineral supplement without lasalocid. Calves were pastured on fescue:bermudagrass paddocks and supplemented with a corn:wheat midds:soybean meal supplement (1.5% of BW/d). Upon arrival, cattle were fed a commercial receiving ration containing 1 g chlorotetracycline/kg for 10 d. Sick calves were administered one or a combination of the following: Nuflor® (florfenicol), Baytril® (eurofloxacin), Micotil® (tilmicosin), or LA 200® (oxytetracycline). Fecal samples were collected immediately prior to ionophore supplementation, approximately midway and at the end of the experimental period (60 d total ionophore feeding) for isolation of E. coli O157:H7 and Salmonella. Putative fecal coliforms were also isolated at these sampling times and examined for antimicrobial susceptibility. The study was replicated over a two year period (year 1, n = 53 hd; year 2, n = 60 hd). Ionophore supplementation had no effect (p > 0.10) on the incidence of calves shedding E. coli O157:H7 or Salmonella. The percentage of calves shedding E. coli O157:H7 varied throughout the experimental period from 0 to 30%, while Salmonella was cultured from only three calves over the two year experimental period. Antimicrobial susceptibility profiles of putative fecal coliforms were consistent with antibiotic treatments administered during the study (observed resistance to chlortetracycline, florfenicol, oxytetracycline), while only one treatment effect was observed. Ionophore treatment resulted in a significantly higher number of coliform isolates resistant to ampicillin compared to controls in year 1 but not year 2. A number of fecal coliform isolates demonstrated resistance to multiple antibiotics, however, this was not affected (p > 0.10) by ionophore supplementation. Mineral intakes, BW gain, and the number of sick calves were similar (p > 0.10) among treatments. Ionophore supplementation had no affect of fecal shedding of E. coli O157:H7 or Salmonella and a negligible impact on antimicrobial susceptibility patterns of fecal coliforms in beef calves.