|Welsh, T - TX A&M UNIVERSITY|
|Soliz, L - TX A&M UNIVERSITY|
|Schroeder, S - TX A&M UNIVERSITY|
Submitted to: Conference on Gastrointestinal Function
Publication Type: Abstract Only
Publication Acceptance Date: January 31, 2005
Publication Date: April 11, 2005
Citation: Edrington, T.S., Callaway, T.R., Genovese, K.J., Schultz, C.L., Welsh, T.H., Soliz, L.A., Schroeder, S.B., Anderson, R.C., Nisbet, D.J. 2005. Ractopamine supplementation decreased fecal shedding of E. coli O157:H7 in naturally-infected beef cattle [abstract]. Conference on Gastrointestinal Function. p. 17. Technical Abstract: The synthetic beta-agonist ractopamine (RAC) improves carcass quality and animal performance. The physiological counterparts to synthetic beta-agonists are the catecholamines, hormones involved in a bacterial quorum-sensing system that regulates virulence gene expression and stimulates growth of E. coli O157:H7 (EHEC). We conducted a study in which yearling beef cattle, naturally-infected with EHEC received RAC, based on our hypothesis that RAC may either directly, or via elevated catecholamines, indirectly increase gut populations and fecal shedding of EHEC. Twenty animals were grouped in an outdoor pen, fed a 80% concentrate ration, and randomly assigned to one of two treatments (10 hd/trt): Control (empty capsule) or RAC (20 mg/hd) dosed daily for 28 days. Animals were restrained in a squeeze chute for administration of treatments, fecal collection and blood sampling. Intermittent shedding patterns of EHEC were observed throughout the study regardless of treatment, with a gradual decline in the number of shedders occurring as the study progressed. Overall, the percentage of cattle shedding EHEC over the 28-d period was lower (P = 0.006) in the RAC (41.8%) compared to Control (58.2%) treatment. No differences (P = 0.87) were observed during the first week of the study, however during the second (P = 0.002) and third (P = 0.006) weeks, the percentage of cattle shedding EHEC was lower in the RAC treatment. This same tendency (P = 0.08) was observed during the fourth week, and while the same percentage of shedders vs non-shedders was observed as in week 2, the difference was not significant due to the decrease in the overall number of animals shedding during week 4. Plasma catecholamine concentrations were similar (P > 0.10) among treatments on days 0, 14, and 28. While results of this preliminary study have potential food safety implications, considering RAC is designed to be fed the last 28 days prior to slaughter, further research is needed to confirm the observations reported herein.