Enteric Diseases of Swine and Cattle: Prevention, Control and Food Safety

NON-TECHNICAL SUMMARY: Escherichia coli O157:H7 is the most common microbial cause of bloody diarrhea in the United States, and a sequel of infection with this organism, the hemolytic uremic syndrome (HUS), can lead to acute renal failure and death especially in children and immuno-compromised persons. It is estimated that every year E. coli O157:H7 causes 73,000 illnesses in the US with 61 resulting in death. The primary source of the infection is from cattle, and people acquire the infection either through direct contact with the animals or through the food chain; it also readily passes from person to person. The purpose of this study is to test the effect of feeding probiotics to steers during the finishing period on the proportion of steers shedding E. coli O157:H7 in the feces
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APPROACH: The study design will be that of a clinical trial conducted on steers in a feedlot setting. One hundred thirty-eight 1-year-old naturally infected steers will be used in the study. The steers will be housed in 24 pens (six steers/pen). The study design will include a complete randomized block design with the initial mean body weight as the blocking factor. The three blocks will each comprise of 8 pens (6 steers per pen), with an average weight of 450kg, 475kg and 490kg or more for block 1, 2, and 3, respectively. Treatment within blocks will be assigned randomly, with twelve pens (4 pens per block) designated treatment group (feed supplemented with probiotics) and another 12 pens (4 pens per block) as the controls (probiotic-free feed). All steers will be housed at the North Dakota States University (NDSU) cattle feedlot facility located in Fargo, ND. In treatment pens, steers will be fed probiotic supplemented finishing diet containing 1 x 109 CFU of Lactobacillus acidophilus (LA 51) and 1 x 109cfu of Propionibacterium freudenreichii (PF 24) (Rosell Probiotics Inc.) per g of feed daily through the finishing period. The probiotics will be stored under refrigeration and reconstituted daily just before mixing with the feed. Steers in control pens will only receive the finishing diet through out the finishing period. Each steer will be restrained in a hydraulic chute, and about 20 g of feces collected from the rectum. A new set of sterile polythene sleeve gloves will be used between collection from subsequent steers. The feces will be put into sterile plastic cups that will be placed on ice before being transported to the laboratory at NDSU for processing. The sampling procedure will be repeated every three weeks for the entire finishing period. Fecal samples will be cultured for E. coli O157:H7 following a standard laboratory protocol that includes immunomagnetic separation and two primer-pair multiplex polymerase chain reaction (PCR) assay that detect genes for Shiga-like toxins 1 (Stx1) and 2 (Stx2). Positive PCR results for E. coli O157:H7 will involve a detection of genes for the somatic antigen O157, the flagellar antigen H7, and at least one or both Shiga toxins (Stx1 or Stx2). Epi Info Version 3.3.2 (Center for Disease Control and Prevention , Atlanta, GA) will be used for statistical analyses. The prevalence of E. coli O157:H7 among the treatment and the control groups will be compared and statistical significance of the difference assessed at an alpha set at 0.05. The effects of pen, block, and sampling times on the recovery E. coli O157:H7 will be investigated. The odds ratio for the recovery of E. coli O157:H7 in both the treatment and control groups through the sampling periods will be calculated.