Reduction of Escherichia coli O157:H7 in Finishing Cattle Fed Corn Genetically Modified to Produce Increased Concentrations of Alpha Amylase in the Corn Kernel

Cattle are recognized as the principal reservoir for Escherichia coli O157:H7 and preharvest food safety efforts often focus on decreasing shedding of this pathogen in cattle feces. Enogen® corn (EC; Syngenta Seeds, LLC) is genetically modified to produce enhanced concentrations of α-amylase in the corn kernel endosperm. Research has demonstrated improvements in feed efficiency for cattle fed EC and research has not yet explored whether improved digestion impacts foodborne pathogen populations in cattle. Therefore, this study explored effects of finishing diets containing EC on Escherichia coli O157:H7 prevalence in cattle. A 2 × 2 factorial experiment was conducted with steers (n = 960) fed diets consisting of 2 types of silage (EC or Control) and grain (EC or Control), fed daily ad libitum. Steers were grouped into 12 blocks by incoming body weight, blocks were randomly assigned to one of four pens, and pens were randomly assigned to one diet. Cattle were sampled using rectoanal mucosal swabs in cohorts of 298-337 cattle per day, for a total of 3 sampling days (15-16 days apart). Escherichia coli O157:H7 prevalence rates ranged from not detected (0/75) to 10.0% (8/80) depending on sampling day. Tests for the silage × corn interaction, and the main effects of silage and corn, were not significant (p > 0.05); however, EC reduced the odds of Escherichia coli O157:H7 prevalence by 43% compared to the control corn diet (p = 0.07). Diets containing EC tended to decrease Escherichia coli O157:H7 prevalence in feedlot cattle; however, this reduction was not significant. Before a conclusion can be drawn about impact of EC on Escherichia coli O157:H7 in cattle, further research is necessary to (1) determine if this tendency is due to increased alpha amylase activity and (2) elucidate impact on Escherichia coli O157:H7 prevalence and concentration, as well as a possible mechanism of action.

Impact of the Probiotic Organism Megasphaera elsdenii on Escherichia coli O157:H7 Prevalence in Finishing Cattle

Feedlot cattle commonly shed the foodborne pathogen Escherichia coli O157:H7 in their feces. Megasphaera elsdenii (ME), a lactic acid-utilizing bacterium, is commonly administered to cattle to avoid lactate accumulation in the rumen and to control ruminal acidosis. The impact of administering ME on foodborne pathogen prevalence, specifically E. coli O157:H7, has not been explored. The purpose of this study was to quantify E. coli O157:H7 prevalence in finishing cattle administered ME. Cattle (n = 448) were assigned to treatments in a randomized complete block design with repeated measurements over two sampling periods. Treatments were arranged as a 2 × 2 factorial containing: ruminally protected lysine (RPL; included for a complementary study) fed at 0% or 0.45% of diet dry matter; with or without ME. Freeze-dried ME was administered as an oral drench (1 × 1010 CFU/steer on day one) and then top dressed onto basal diets (1 × 107 CFU/steer) daily thereafter. Rectoanal mucosal swabs (RAMS) were obtained from animals before harvest to determine the E. coli O157:H7 prevalence. The inclusion of RPL (P = 0.2136) and ME (P = 0.5012) did not impact E. coli O157:H7 prevalence, and RPL was not included in any significant interactions (P > 0.05). A significant interaction was observed between ME and sampling period (P = 0.0323), indicating that the effect of ME on E. coli O157:H7 prevalence varied over the sampling period. A diet containing ME reduced the odds of E. coli O157:H7 prevalence by 50% during sampling period 1 (8.0% and 14.7% for cattle with and without ME, respectively) and increased the odds by 23% during sampling period 2 (10.8% and 8.9% for cattle with and without ME, respectively). Administering ME in cattle diets did not impact E. coli O157:H7 in feedlot cattle. This is the first study to investigate the use of ME as a preharvest food safety intervention in cattle, and additional research is necessary to determine the efficacy.

333 Effects of ruminally-protected lysine and Megasphaera elsdenii on performance and carcass characteristics of finishing cattle

Crossbred steers (n = 448; 352 ± 25 kginitial body weight) were used to evaluate impact of Megasphaera elsdenii (ME; Lactipro advance, MS Biotec, Wamego, KS), alone or in combination with ruminally-protected lysine (RPL; USA Lysine, Kemin Industries, Inc., USA), on performance and carcass traits of finishing steers in a randomized complete block design. Steers were blocked by initial body weight and randomly assigned within block to one of 64 pens (7 steers/pen) in a 2 x 2 factorial treatment arrangement. Factors consisted of RPL (0 or 40 g/steer daily) and two step-up regimens (21-d without ME or 10-d with ME). Four step-up diets were used to transition cattle to finishing diets containing (dry basis) 60% steam flaked corn, 7% wheat straw, 30% sweet bran, and supplement. Diets were fed once daily ad libitum. Freeze-dried ME was re-hydrated and dosed orally (1x1010 CFU/steer) on d 1, and top-dressed (1x107 CFU/steer daily) onto diets daily thereafter. Data were analyzed using a mixed model with ME, RPL and the interaction as fixed effects, and block as the random effect. There were no interactions between ME and RPL (P > 0.05). Steers given ME consumed 16% less roughage compared to their counterparts without (P < 0.05), but gain, dry matter intake, and gain:feed were similar (P > 0.10). Administering ME tended to increase percentage of USDA Prime carcasses (0.5 vs 2.7%; P < 0.06). Feeding RPL did not affect feedlot performance, carcass weight, longissimus muscle area, marbling score, 12th-rib fat thickness, or liver abscess incidence (P > 0.10), but tended to increase yield grade (P < 0.07). In conclusion, use of Megasphaera elsdenii with an accelerated step-up program yielded feedlot performance and carcass traits comparable to those of cattle adapted with a conventional, 21-d step-up program, but supplemental lysine was without effect.

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