|Genovese, Kenneth - Ken|
|Nisbet, David - Dave|
Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2006
Publication Date: 10/20/2006
Citation: Edrington, T.S., Callaway, T.R., Ives, S., Engler, M.J., Welsh, T.H., Hallford, D.M., Genovese, K.J., Anderson, R.C., Nisbet, D.J. 2006. Effect of ractopamine HC1 supplementation on fecal shedding of Escherichia coli O157:H7 and Salmonella in feedlot cattle. Current Microbiology. 53:340-345. Interpretive Summary: Ractopamine is a compound fed to cattle prior to slaughter to improve feedlot performance and carcass quality. Ractopamine is similar to some hormones that have been shown to affect growth of E. coli O157:H7. The purpose of the present study was to determine if feeding ractopamine has any impact on E. coli and Salmonella in feedlot cattle. Results showed that ractopamine feeding decreased fecal shedding of E. coli O157:H7 and increased shedding of Salmonella in cattle. This work is important in understanding how livestock feed additives might have implications for microbial food safety of meat products reaching the American consumer.
Technical Abstract: The effects of the beta-agonist ractopamine, recently approved for use in feedlot cattle to improve carcass quality and performance, was examined on fecal shedding of E. coli O157:H7 and Salmonella in feedlot cattle. In the first study, 20 feedlot steers and heifers were randomly assigned to receive either 0 (control) or 20 mg ractopamine/hd•d**-1 via oral bolus for 28 days. Fecal samples were collected daily and shedding of E. coli O157:H7 determined via immuno-magnetic separation. The percentage of animals shedding E. coli O157:H7 was not different (P > 0.10) the first week of the study, but was decreased (P < 0.05) in the second and third weeks, and tended (P < 0.10) to be lower during the fourth week of the experimental period, compared with control animals. When examined over the entire 28-d experimental period, ractopamine decreased (P = 0.0006) the percentage cattle shedding E. coli O157:H7 (58 vs 42% for control and ractopamine treatments, respectively). Serum catecholamine concentrations were not affected (P > 0.10) by treatment. A second study was conducted in a commercial feedlot facility in the southwestern United States. Eighteen pens of crossbred beef heifers (approx. 100 hd/pen; 9 pens/treatment) were randomly assigned to receive either 0 (control) or 200 mg ractopamine/hd•d**-1. Treatment starting dates were staggered such that there were three replicates (six pens/replicate) in the experiment. Fresh fecal samples (30/pen) were collected off the pen floor using sterile palpation sleeves, prior to ractopamine supplementation and again after approximately 28 d of ractopamine supplementation (within a few days of slaughter), and cultured for E. coli O157:H7 and Salmonella. The percentage of animals shedding E. coli O157:H7 was decreased (P < 0.05) in the third replicate and when data was pooled across replicates (P = 0.05) in ractopamine-treated cattle, compared with controls. The percentage of animals shedding Salmonella was higher (P < 0.05) in ractopamine-treated cattle compared with controls in the third replicate, and tended to be higher (P = 0.08) when data was pooled across replicates. Reasons for the decreased shedding of E. coli O157:H7 are unknown, while the increase in Salmonella may possibly be attributed to the decrease in other gram-negative bacteria, such as E. coli O157:H7, giving Salmonella a competitive advantage. While further research is required to confirm these results, the potential food safety implications of this research are intriguing.