Influence of wet distiller's grains on prevalence of Escherichia coli O157:H7 and Salmonella in feedlot cattle and antimicrobial susceptibility of generic Escherichia coli isolates.

The current research examined the inclusion of 20% wet distiller's grains (WDG) fed with steam-flaked corn (SFC) or dry-rolled corn (DRC) in diets fed to feedlot cattle on fecal prevalence of Escherichia coli O157:H7 and Salmonella. Crossbred beef heifers (n = 272; average initial body weight (BW) = 354 kg) were blocked by BW and pen size and randomly assigned to treatment. Fecal samples from freshly voided fecal pats were collected from each pen on the day cattle shipped for slaughter (237 fecal samples: 72, 125, and 40 from cattle 132, 160, and 181 days on feed, respectively). Fecal samples were cultured quantitatively and qualitatively for the above pathogens. Populations of E. coli O157:H7 and Salmonella were generally low with very few samples containing quantifiable populations. Similarly, after enrichment, few samples were E. coli O157:H7 positive in any collection with no treatment differences (p > 0.10). More samples were Salmonella positive during the first collection with an increased (p < 0.05) prevalence observed in the SFC and DRC treatments compared with DRC + WDG treatment. No other treatment differences were observed for Salmonella. Putative fecal coliform isolates (18 per treatment; first collection) were examined for antimicrobial susceptibility, and the majority were susceptible to all of the antibiotics examined. Most of the resistance was observed in the SFC (n = 3) and DRC (n = 4) treatments, and only one isolate in each of the two WDG treatments demonstrated resistance (one antibiotic each, streptomycin and tetracycline). All multidrug resistance (2-4 antibiotics) was observed in isolates cultured from the DRC and SFC treatments (n = 2 isolates in each treatment). Results of the current research found no significant effect of feeding WDG to feedlot cattle on fecal prevalence, at time of shipment for slaughter, of E. coli O157:H7, and only modest differences (decreases) in Salmonella prevalence with no apparent affect on antimicrobial susceptibility of fecal coliform isolates.