Effects of concentrate level of diet and pen configuration on prevalence of Escherichia coli O157 in finishing goats

Boer-sired goat kids (n = 181) from native pastures were transported to outdoor pens in a beef cattle research facility to evaluate the effects of dietary concentrate level and pen configuration on prevalence of Escherichia coli O157 and to determine if horizontal transmission of E. coli O157 occurs between goats and cattle. Goats were blocked into heavy and light BW groups and randomly assigned to 12 pens, with each containing 15 or 16 animals. Treatments were randomly assigned to pens in a 3 x 2 factorial arrangement. Dietary treatments consisted of diets containing 50, 70, or 90% of the total diet (DM basis) as concentrate, with the balance of the diet as alfalfa hay. Goats were housed in pens with concrete floors, and a large concrete block (45 cm x 75 cm x 150 cm) was placed in the center of 6 of the 12 pens, thus providing two different pen configurations. Fecal samples were collected on day 0, 20, 34, 55, 83, and 105, and cultured for E. coli O157. Feces from cattle housed in adjacent pens were also sampled on day 1, 20, and 34. Isolation and identification of E. coli O157 from fecal samples were by selective enrichment in a broth, followed by immunomagnetic separation and plating on cefixime, tellurite, sorbitol MacConkey agar. Sorbitol-negative colonies that were positive for indole production, positive for O157 antigen agglutination, and speciated by API test, were considered as E. coli O157. Pulsed-field gel electrophoresis (PFGE) of chromosomal DNA was performed on all E. coli O157 isolates to characterize the genetic types and to determine if horizontal transfer of strains occurred between cattle and goats. Detection of the attaching and effacing gene (eae), shiga toxin-1 and -2 genes (stx1 and stx2) was done by polymerase chain reaction (PCR). Mean prevalence of E. coli O157 across all treatments and sampling days was 4.6% and no statistical differences (P > 0.10) were observed for the different pen configurations or diet concentrate levels, but prevalence was numerically higher in the 70% concentrate treatment on 4 of the 6 sampling days. The eae and stx2 genes were present in 95% of the isolates, but the stx1 gene was present in only 51% of the isolates. One E. coli O157 isolate from a goat shared a common PFGE subtype with cattle isolates. Results suggest that in goats with low prevalence of E. coli O157 the level of concentrate in the diet did not influence the shedding pattern.