182 Evaluating effects of an abrupt shift to varying forage qualities on E. coli and coliform shedding in beef cattle.

Abstract Foodborne pathogenic bacteria are often found in the gut of cattle, including those which pose significant concerns to human consumers such as E. coli O157:H7 and other Shiga-toxin producing E. coli (STEC) which are classified as adulterants in ground beef. High starch-containing diets have been linked to the intestinal proliferation of E. coli, while forages caused decreases in E. coli fecal shedding However, the effects of an abrupt dietary shift and different forage qualities on E. coli shedding in beef cattle remains unknown. The study aimed to evaluate the influence of changing diets from high grain to high-quality and low-quality forage rations on fecal E. coli and coliform shedding. Twenty-seven (n =27) crossbred beef steers and heifers from the University of Georgia Double Bridges Farm were enrolled in a 43-day randomized design block design. Cattle were blocked based on weight and sex and on Day 0 assigned to 1 of 3 treatments: 1) Finishing-high grain Diet (CTRL), 2) Low-Quality Forage (LQF), and 3) High-Quality Forage (HQF). The initial 21 days cattle were adapted to the high-grain diet, followed by an abrupt shift to their respective treatments for an additional 22 days. Fecal samples were collected via rectal fecal grabs on days 0, 21, 23, 25, 29, and 43. Samples were serially diluted (10-fold increments), plated on Petrifilm® E. coli/Coliform Count Plates, and incubated for 24 hours at 35° C for enumeration. Across all time points, a TRT´DAY interaction was observed for both E. coli (P = 0.0022) and Coliforms (P = 0.0036) populations. Eight days post-shift (day 29), E. coli populations in the LQF group were decreased by 1.15 log10 CFU/g compared to CTRL as well as a reduction in coliforms. On day 43, E. coli populations in the LQF group remained lower than in the HQF group but were not different from CTRL. Coliform populations in the LQF group remained lower than both the CTRL and HQF groups on day 43. While abruptly transitioning finishing beef cattle to hay remains impractical, a >1 log10 CFU/g reduction in E. coli and coliforms suggests that LQF may hold the key to understanding which specific chemical nutrient components drive E. coli and coliform shedding and will indicate which feeds can practically be used in beef cattle finishing rations. Further research is needed to identify these components to decrease contamination risks to the public.