J. T. Fox

Effects of feeding wet corn distillers grains with solubles with or without monensin and tylosin on the prevalence and antimicrobial susceptibilities of fecal foodborne pathogenic and commensal bacteria in feedlot cattle.

Distillers grains, a coproduct of ethanol production from cereal grains, are composed principally of the bran, protein, and germ fractions and are commonly supplemented in ruminant diets. The objective of this study was to assess the effect of feeding wet distillers grains with solubles (WDGS) and monensin and tylosin on the prevalence and antimicrobial susceptibilities of fecal foodborne and commensal bacteria in feedlot cattle. Cattle were fed 0 or 25% WDGS in steam-flaked corn-based diets with the addition of no antimicrobials, monensin, or monensin and tylosin. Fecal samples were collected from each animal (n = 370) on d 122 and 136 of the 150-d finishing period and cultured for Escherichia coli O157. Fecal samples were also pooled by pen (n = 54) and cultured for E. coli O157, Salmonella, commensal E. coli, and Enterococcus species. Antimicrobial resistance was assessed by determining antimicrobial susceptibilities of pen bacterial isolates and quantifying antimicrobial resistance genes in fecal samples by real-time PCR. Individual animal prevalence of E. coli O157 in feces collected from cattle fed WDGS was greater (P < 0.001) compared with cattle not fed WDGS on d 122 but not on d 136. There were no treatment effects on the prevalence of E. coli O157 or Salmonella spp. in pooled fecal samples. Antimicrobial susceptibility results showed Enterococcus isolates from cattle fed monensin or monensin and tylosin had greater levels of resistance toward macrolides (P = 0.01). There was no effect of diet or antimicrobials on concentrations of 2 antimicrobial resistance genes, ermB or tetM, in fecal samples. Results from this study indicate that WDGS may have an effect on the prevalence of E. coli O157 and the concentration of selected antimicrobial resistance genes, but does not appear to affect antimicrobial susceptibility patterns in Enterococcus and generic E. coli isolates.

Effects of Dried Distillers' Grain on Fecal Prevalence and Growth of Escherichia coli O157 in Batch Culture Fermentations from Cattle†

ABSTRACT Distillers’ grains (DG), a by-product of ethanol production, are fed to cattle. Associations between Escherichia coli O157 prevalence and feeding of DG were investigated in feedlot cattle (n = 379) given one of three diets: steam-flaked corn (SFC) and 15% corn silage with 0 or 25% dried distillers’ grains (DDG) or SFC with 5% corn silage and 25% DDG. Ten fecal samples were collected from each pen weekly for 12 weeks to isolate E. coli O157. Cattle fed 25% DDG with 5 or 15% silage had a higher (P = 0.01) prevalence of E. coli O157 than cattle fed a diet without DDG. Batch culture ruminal or fecal microbial fermentations were conducted to evaluate the effect of DDG on E. coli O157 growth. The first study utilized microbial inocula from steers fed SFC or dry-rolled corn with 0 or 25% DDG and included their diet as the substrate. Ruminal microbial fermentations from steers fed DDG had higher E. coli O157 contents than ruminal microbial fermentations from steers fed no DDG (P < 0.05) when no substrate was included. Fecal fermentations showed no DDG effect on E. coli O157 growth. In the second study with DDG as a substrate, ruminal fermentations with 0.5 g DDG had higher (P < 0.01) E. coli O157 concentrations at 24 h than ruminal fermentations with 0, 1, or 2 g DDG. In fecal fermentations, 2 g DDG resulted in a higher concentration (P < 0.05) at 24 h than 0, 0.5, or 1 g DDG. The results indicate that there is a positive association between DDG and E. coli O157 in cattle, and the findings should have important ramifications for food safety.

Feeding Supplemental Dried Distiller’s Grains Increases Faecal Shedding of Escherichia coli O157 in Experimentally Inoculated Calves

Escherichia coli O157 is an important foodborne pathogen and asymptomatic cattle serve as major reservoirs for human infection. We have shown a positive association between feeding distiller’s grains and E. coli O157 prevalence in feedlot cattle. The objective of this study was to determine the effect of feeding dried distiller’s grain (DDG) on faecal shedding of E. coli O157 in calves experimentally inoculated with E. coli O157. Holstein calves (five per treatment group), fed steam‐flaked corn‐based high‐grain diets supplemented with 0% (control) or 25% DDG, were orally inoculated with a five‐strain mixture (6 × 109 CFU/calf) of nalidixic acid‐resistant (NalR) E. coli O157. Faecal samples were taken three times per week for 6 weeks to determine the prevalence and concentration of NalRE. coli O157. At the end of the study (day 43), calves were euthanized and necropsied. Ruminal, caecum, colon, and rectal contents, and rectoanal mucosal swab (RAMS) samples were collected at necropsy to determine NalRE. coli O157 concentration. There was a trend for an interaction between treatment and faecal sampling day. The concentration of NalRE. coli O157 in the faeces was significantly higher in faecal samples from calves fed DDG compared with control calves on days 35, 37, 39 and 42. At necropsy, the concentration of NalRE. coli O157 was higher in the caecum (P = 0.01), colon (P = 0.03) and rectum (P = 0.01) from calves fed DDG compared with control animals. The number of sites at necropsy positive for NalRE. coli O157 was higher in calves fed DDG compared with calves in the control treatment (P < 0.001). Our results indicate that E. coli O157 gut persistence and faecal prevalence increased in calves fed DDG, which potentially have important implications for food safety.

Antimicrobial susceptibility of foodborne pathogens in organic or natural production systems: an overview.

Organic and natural food production systems are increasing in popularity, at least partially because consumers perceive that these niche markets provide healthier and safer food products. One major difference between these niche markets and conventional production systems is the use of antimicrobials. Because antimicrobial agents exert selective pressures for antimicrobial resistance, relating antimicrobial susceptibility of foodborne bacteria to niche market production systems is of interest. Other differences between production systems might also influence the susceptibility of foodborne pathogens. The objective of this review is to compare the impact of food animal production systems on the antimicrobial susceptibility of common foodborne bacterial pathogens. Studies comparing the susceptibility of such pathogens were diverse in terms of geographic location, procedures, species of bacteria, and antimicrobials evaluated; thus, it was difficult to draw conclusions. The literature is highly variable in terms of production type and practices and susceptibility associations, although few studies have compared truly organic and conventional practices. When statistical associations were found between production type and minimum inhibitory concentrations or percentage of isolates resistant for a particular pathogen, the isolates from conventionally reared animals/products were more commonly resistant than the comparison group (organic, antibiotic free, etc.). Therefore, further studies are needed to better assess public health consequences of antimicrobial resistance and food animal production systems, specifically organic or natural versus conventional.

Associations between weather conditions during the first 45 days after feedlot arrival and daily respiratory disease risks in autumn-placed feeder cattle in the United States

Data on associations between weather conditions and bovine respiratory disease (BRD) morbidity in autumn-placed feedlot cattle are sparse. The goal of our study was to quantify how different weather variables during corresponding lag periods (considering up to 7 d before the day of disease measure) were associated with daily BRD incidence during the first 45 d of the feeding period based on a post hoc analysis of existing feedlot operational data. Our study population included 1,904 cohorts of feeder cattle (representing 288,388 total cattle) that arrived to 9 US commercial feedlots during September to November in 2005 to 2007. There were 24,947 total cases of initial respiratory disease (animals diagnosed by the feedlots with BRD and subsequently treated with an antimicrobial). The mean number of BRD cases during the study period (the first 45 d after arrival) was 0.3 cases per day per cohort (range = 0 to 53.0), and cumulative BRD incidence risks ranged from 0 to 36% within cattle cohorts. Data were analyzed with a multivariable mixed-effects binomial regression model. Results indicate that several weather factors (maximum wind speed, mean wind chill temperature, and temperature change in different lag periods) were significantly (P < 0.05) associated with increased daily BRD incidence, but their effects depended on several cattle demographic factors (month of arrival, BRD risk code, BW class, and cohort size). In addition, month and year of arrival, sex of the cohort, days on feed, mean BW of the cohort at entry, predicted BRD risk designation of the cohort (high or low risk), cohort size, and the interaction between BRD risk code and arrival year were significantly (P < 0.05) associated with daily BRD incidence. Our results demonstrate that weather conditions are significantly associated with BRD risk in populations of feedlot cattle. Defining these conditions for specific cattle populations may enable cattle health managers to predict and potentially manage these effects more effectively; further, estimates of effects may contribute to the development of quantitative predictive models for this important disease syndrome.

Prevalence of Escherichia coli O157:H7 in Organically and Naturally Raised Beef Cattle

ABSTRACT We determined the prevalence of Escherichia coli O157:H7 in organically and naturally raised beef cattle at slaughter and compared antibiotic susceptibility profiles of the isolates to those of isolates from conventionally raised beef cattle. The prevalences of E. coli O157:H7 were 14.8 and 14.2% for organically and naturally raised cattle, respectively. No major difference in antibiotic susceptibility patterns among the isolates was observed.

Prevalence of Escherichia coli O157:H7 in gallbladders of beef cattle.

ABSTRACT Gallbladders and rectal contents were collected from cattle (n = 933) at slaughter to determine whether the gallbladder harbors Escherichia coli O157:H7. Both gallbladder mucosal swabs and homogenized mucosal tissues were used for isolation. Only five gallbladders (0.54%) were positive for E. coli O157:H7. Fecal prevalence averaged 7.1%; however, none of the cattle that had E. coli O157:H7 in the gallbladder was positive for E. coli O157:H7 in feces. Therefore, the gallbladder does not appear to be a common site of colonization for E. coli O157:H7 in beef cattle.

Evaluation of feeding dried distiller's grains with solubles and dry-rolled corn on the fecal prevalence of Escherichia coli O157:H7 and Salmonella spp. in cattle.

Escherichia coli O157:H7 and Salmonella are foodborne pathogens that reside in the gut of cattle and are shed in the feces. Previous work indicated a positive association between feeding cattle distillers grains (DG) and an increase in E. coli O157:H7 prevalence. Feeding processed grains also has been shown to affect fecal prevalence of E. coli O157:H7. The objective of this study was to evaluate the effect of feeding DG and dry-rolled corn (DRC), alone or in combination, on fecal prevalence of E. coli O157:H7 and Salmonella in finishing cattle. Cattle were allotted to pens (n = 28), and fed dietary treatments (n = 150 days) structured in a 2 x 2 factorial arrangement; the factors were 0% or 25% dried corn DG with solubles (DDGS) and 0% or 25% DRC in steam-flaked corn-based high-grain diets. Fecal samples were collected from each pen floor before initiating dietary treatments and at least once every 2 weeks after final diets began. Overall prevalence of E. coli O157:H7 in fecal samples was 5.1%. There were no significant effects of DDGS, DRC, or sampling time on E. coli O157:H7 prevalence (p > 0.20). Overall prevalence of Salmonella in pen floor fecal samples was 23.7%, and sampling week affected prevalence (p < 0.01), ranging from < 1% (week 1) to 77.5% (week 17). Salmonella prevalence was not affected by cattle diet, and no work had previously reported an association between either DG or DRC and Salmonella prevalence. Lack of an association between E. coli O157:H7 prevalence and feeding DG or DRC is contrary to previous observations. Further research is needed to understand inconsistencies between studies of E. coli O157:H7 prevalence and potential associations with DG and grain-processing methods.

Effects of mucin and its carbohydrate constituents on Escherichia coli O157 growth in batch culture fermentations with ruminal or fecal microbial inoculum.

In cattle, Escherichia coli O157 generally persists in the large intestine more often than in the rumen. In contrast to the rumen, the large intestine is lined by an epithelial membrane that secretes mucus. We hypothesize that substrates contained in intestinal mucus may constitute a source of energy that is preferentially used by E. coli O157. Therefore, our objective was to test the effects of mucin and its carbohydrate constituents on in vitro growth of E. coli O157 in ruminal or fecal microbial fermentations. Ruminal contents and feces were collected from a ruminally cannulated donor steer fed a corn grain-based finishing diet. Ruminal contents were strained through 2 layers of cheesecloth and incubated at 39 degrees C for 1 h; the floating hay mat was removed with a vacuum suction; and the remaining material was utilized as rumen microbial inoculum. Feces were suspended in physiologic saline to increase fluidity, blended, and strained through 2 layers of cheesecloth. The resulting fluid was utilized as fecal microbial inoculum. Fermentations (50 mL) were performed in serum bottles with a 2:1 mineral buffer to microbial inoculum ratio. Substrates (mucin, fucose, galactose, mannose, gluconic acid, galacturonic acid, glucuronic acid, galactosamine, and glucosamine) were added at 10 mg/mL. A mixture of 5 strains of nalidixic acid-resistant (Nal(R)) E. coli O157 strains was added to each fermentation and concentrations were determined after 0, 6, 12, and 24 h of incubation. In ruminal fermentations, fucose, mannose, glucuronic acid, galacturonic acid, glucosamine, galactosamine, and mucin had no effect on Nal(R) E. coli O157 concentration compared with the control (no substrate added) fermentation. At 24 h of fermentation, the mean concentration of Nal(R) E. coli O157 in fermentations with galactose was less than the control. However, including gluconic acid as substrate increased Nal(R) E. coli O157 concentration at 24 h. In fecal fermentations, mannose, galactose, gluconic acid, glucuronic acid, galacturonic acid, glucosamine, and mucin increased Nal(R) E. coli O157 growth compared with control at 24 h, whereas galactosamine and fucose did not. Gluconic acid was the most stimulatory substrate, increasing Nal(R) E. coli O157 by more than 1.0 log in ruminal fermentations and 2.0 log in fecal fermentations. In summary, availability of mucous constituents, particularly gluconic acid, may explain the greater prevalence of E. coli O157 in the large intestine compared with the rumen of the digestive tract.

Optimizing use of wet sorghum distiller’s grains with solubles in flaked-corn finishing diets

A finishing trial was conducted using 637 heifers (initially 849 lb) to determine the optimal amount of wet sorghum distillers grains with solubles (WDGS) in finishing diets containing steam-flaked corn. Dietary treatments consisted of six concentrations of WDGS (0, 8, 16, 24, 32, and 40%; dry basis). Heifers were placed into dirt-surfaced feedlot pens (25 to 30 heifers/pen; 4 pens/treatment) and fed for 58 days. Daily gain responded in a quadratic manner (P<0.01), peaking with 8% WDGS in the finishing diet. Average daily gains during the 58-day finishing period were 2.79, 3.11, 3.05, 2.89, 2.70, and 2.55 lb/day for cattle fed 0, 8, 16, 24, 32, and 40% WDGS, respectively. Dry matter intake decreased linearly (P<0.01) as content of WDGS increased. Feed efficiency was optimized with 16% WDGS (6.81, 6.49, 6.19, 6.64, 6.96, and 7.18 lb dry feed per lb gain for cattle fed 0, 8, 16, 24, 32, and 40% WDGS, respectively). Animal performance data were used to compute net energy gain (NEg) values of each diet, yielding estimates of 69.9, 71.7, 75.8, 71.2, 68.9, and 67.6 Mcal/cwt for diets containing 0, 8, 16, 24, 32, and 40% WDGS, respectively (quadratic effect, P<0.03). Ribeye area decreased linearly (P<0.02) as concentration of WDGS increased in the diet. The percentage of USDA Yield Grade 1 carcasses decreased linearly (P<0.05), and the percentage of USDA Yield Grade 3 carcasses increased linearly (P=0.05) as the content of WDGS was increased. Average USDA Yield Grade increased linearly (P<0.02) as content of WDGS was increased. Grid-based carcass values were not significantly different across dietary treatments. Regression analysis of efficiency data indicates that the optimum amount of sorghum WDGS in steam-flaked corn diets is approximately 15%. Diets containing as much as 24% WDGS yielded efficiencies equal or superior to diets containing no WDGS.