Determination of the mechanism(s) by which direct-fed microbials control Escherichia coli O157:H7 in cattle

Abstract

Scope and Method of Study: The purpose of this experiment was to investigate the possible mechanisms responsible for the success of the direct-fed microbials, Lactobacillus acidophilus and Propionibacterium freudenreichii (included in and marketed as Bovamine(R), in controlling Escherichia coli O157:H7 in cattle. In order to do this an E. coli O157:H7 challenge was conducted with ten steers. Five were fed the direct-fed microbials and five were fed the control treatment, lactose (direct-fed microbial carrier). Immunoglobulins, blood chemistry, complete blood counts, performance measures, and carriage of E. coli O157:H7 were measured throughout the trial.

Findings and Conclusions: An increased level of serum IgA was observed in the direct-fed microbial group post-challenge. The direct-fed microbial group also showed an increased amount of blood granulocytes and granulocytes as a percentage of white blood cells post-challenge. The direct-fed microbial group had a higher post challenge increase in total lymphocytes while the control group had higher lymphocytes as a percentage of white blood cells post-challenge. The control group had higher dry matter intakes. Both groups exhibited similar levels of all measurements prior to the challenge.