Effect of Crude Glycerin on Fecal Shedding of Escherichia coli O157 in Growing and Finishing Cattle

Two experiments were conducted to evaluate the effects of crude glycerin feeding on E. coli O157 prevalence in feces of growing and finishing cattle. In study 1, crude glycerin was included at 0, 4 or 8% of dry matter in growing cattle diets comprised of 62.5% corn silage and 33, 28, or 24% wet corn gluten feed. Heifers (n = 368; initial body weight = 234 +/- 3.2 kg) were housed in partially covered, concrete-surfaced pens with seven to eight animals per pen and 16 pens per treatment for the 90-day experiment. Study 2 was a finishing experiment with a 2 x 2 factorial treatment arrangement. Factor 1 consisted of the level of crude glycerin (0 or 2% of dry matter) and factor 2 was the presence or absence of a combination of 25% soybean hulls and 15% wet distiller's grains (WDG) as grain substitutes. Heifers (n = 232; initial body weight = 427 +/- 8.8 kg) were housed in concrete-surfaced pens with seven to eight animals per pen and eight pens per treatment. Fresh fecal samples were taken from growing and finishing animals via rectal palpation. One gram of feces was incubated for 6 hr at 40 degrees C in Gram negative broth with cefixime (0.05 mg/L), cefsulodin (10 mg/L), and vancomycin (8 mg/L), and then subjected to immunomagnetic separation with E. coli O157 beads. Recovered beads were plated onto MacConkey agar with sorbitol, cefixime, and tellurite (CT-SMAC), and non-sorbitol fermenting colonies were tested for indole production and O157 antigen agglutination. Positive colonies for both tests were confirmed as E. coli using the API 20E kit. Fecal prevalence rates of E. coli 0157 were affected by sampling clay in the growing study (P <0.01) but not in the finishing study (P > 0.1). Increasing levels of crude glycerin decreased incidence of E. coli O157 in growing cattle (linear effect, P <0.01; 4.4, 3.2, and 1.8% for heifers fed 0, 4, and 8% glycerin, respectively), but had no significant effect in finishing cattle (P > 0.05) despite a strong tendency for a decrease in finishing cattle receiving corn-based diets (P = 0.059). There was no interaction between WDG inclusion and glycerin level (P > 0.1) and no WDG effect on prevalence of E. coli O157 in finishing cattle (P > 0.1). Glycerin may be useful as a means for decreasing fecal prevalence of E. coli O157 in cattle, but effects may depend on the type of diet that is fed.