Title:
Effects of wheat or corn distillers dried grains with solubles on feedlot performance, fecal shedding, and persistence of Escherichia coli O157:H7.

Abstract:
Distillers dried grains with solubles (DDGS) are a coproduct of the ethanol industry and are often used as a replacement for grain in livestock production. Feeding corn DDGS to cattle has been linked to increased fecal shedding of Escherichia coli O157:H7, although in Canada, DDGS are often produced from wheat. This study assessed the effects of including 22.5% wheat or corn DDGS (DM basis) into barley-based diets on performance, carcass characteristics, animal health, and fecal E. coli O157:H7 shedding of commercial feedlot cattle. Cattle (n = 6,817) were randomly allocated to 10 pens per treatment group: WDDGS (diets including 22.5% wheat DDGS), CDDGS (diets including 22.5% corn DDGS), or CTRL (barley substituted for DDGS). Freshly voided fecal pats (n = 588) were collected and pooled monthly for fecal pH measurement and screened for naturally occurring E. coli O157:H7 by immunomagnetic separation (IMS) and direct plating (DP). Hide swabs (n = 367) were collected from randomly selected cattle from each pen before slaughter. Pen-floor fecal samples (n = 18) were collected from treatment groups at entry to the feedlot (<14 d on the finishing diet) and after adapting to the finishing diet for ≥ 14 d, inoculated (10(9) cfu of a 5 strain naldixic acid-resistant E. coli O157:H7 mixture), incubated (20°C) and evaluated weekly (IMS and DP) to assess fecal E. coli O157:H7 persistence. The WDDGS group had 3.0% poorer ADG (P = 0.007), 5.3% poorer G:F (P < 0.001), and a decreased proportion of Canada Quality Grade AAA carcasses (P = 0.022) compared with CTRL cattle. The CDDGS group had a similar ADG (P = 0.06), a decreased proportion of Canada Yield Grade (YG) 1 (P < 0.001), and greater proportions of Canada YG 2 (P = 0.003) and YG 3 (P < 0.001) carcasses compared with the CTRL group. There were no differences among groups in any of the animal health parameters assessed. Inclusion of DDGS in cattle finishing diets had no effect on fecal shedding (P = 0.650) or persistence (P = 0.953) of E. coli O157:H7. However, feces from cattle on starter diets <14 d had longer persistence of E. coli O157:H7 (week) than cattle on finishing diets ≥ 14 d (P < 0.003). Inclusion of DDGS in feedlot diets depends on commodity pricing relative to that of barley and for WDDGS must also include the risk of feedlot performance and carcass grading disadvantages. Feeding cattle barley based-diets with 22.5% corn or wheat DDGS did not affect fecal shedding of E. coli O157:H7.