Effects of using retention-pond water for dust abatement on performance of feedlot steers and carriage of Escherichia coli O157 and Salmonella spp

An Experimental Field Trial Investigating the Use of Bacteriophage and Manure Slurry Applications in Beef Cattle Feedlot Pens for Salmonella Mitigation

Post-harvest Salmonella mitigation techniques are insufficient at addressing Salmonella harbored in cattle lymph nodes, necessitating the exploration of pre-harvest alternatives that reduce Salmonella prior to dissemination to the lymph nodes. A 2 × 2, unbalanced experiment was conducted to determine the effectiveness of pre-harvest treatments applied to the pen surface for Salmonella mitigation in cattle. Treatments included manure slurry intended to mimic pen run-off water (n = 4 pens), a bacteriophage cocktail (n = 4), a combination of both treatments (n = 5), and a control group (n = 5) that received no treatment. Environment samples from 18 feedlot pens and fecal grabs, hide swabs, and subiliac lymph nodes from 178 cattle were collected and selectively enriched for Salmonella, and Salmonella isolates were sequenced. The combination treatment was most effective at reducing Salmonella, and the prevalence was significantly lower compared with the control group for rump swabs on Days 14 and 21. The treatment impact on Salmonella in the lymph nodes could not be determined due to low prevalence. The reduction on cattle hides suggests that bacteriophage or water treatments applied to the feedlot pen surface may reduce Salmonella populations in cattle during the pre-harvest period, resulting in reduced contamination during slaughter and processing.

Efficacy of a Salmonella Siderophore Receptor Protein Vaccine on Fecal Shedding and Lymph Node Carriage of Salmonella in Commercial Feedlot Cattle

The efficacy of a Salmonella vaccine for reducing fecal shedding of Salmonella during the finishing period and lymph node (LN) carriage at harvest was investigated in commercial feedlot cattle. The study was designed as a pen-level randomized complete block with two treatment groups, a Salmonella Newport siderophore receptor and porin proteins-based vaccine (VAC) and a nonvaccinated control (CON). Cattle were randomly allocated into 24 pens within 12 blocks based on the time of allocation. Twenty to 25 fecal pats were collected from each of the study pen floors once a month from June to August 2013. During harvest, a minimum of 25 sub-iliac LN were collected from carcasses within each study pen. Fecal and pulverized LN samples were cultured for Salmonella quantification and detection. Mixed models were used to analyze the effect of vaccination on fecal shedding and LN carriage of Salmonella. Montevideo and Anatum were the predominant Salmonella serotypes among fecal samples and LNs; no Newport isolates were recovered. Vaccination was not significantly associated (p = 0.57) with the prevalence of Salmonella in feces over time; the mean within-pen prevalence was 62.3% and 66.0% among VAC and CON, respectively. Sampling month was significantly associated (p < 0.01) with fecal prevalence; mean prevalence was 71.4% for June, 48.6% for July, and 70.8% for August. Across all pens, the cumulative prevalence of Salmonella in LN was 86.4%. Vaccination resulted in no significant reduction in LN prevalence (p = 0.52); mean prevalence was 85.7% for VAC and 87.4% for CON groups. Although vaccinated cattle had numerically fewer Salmonella LN and fecal positives, there were no statistically significant vaccine effects. Potential reasons for the lack of vaccine efficacy could include an overwhelming Salmonella exposure, a lack of cross-protection against non-Newport serotypes, and insufficient duration of immunity relative to harvest.

Investigation into Possible Differences in Salmonella Prevalence in the Peripheral Lymph Nodes of Cattle Derived from Distinct Production Systems and of Different Breed Types

Previous research demonstrated significant variation in the prevalence of Salmonella in peripheral lymph nodes (LNs) of feedlot cattle and cull cows, with greater prevalence in feedlot cattle. Therefore, we performed experiments to investigate whether these differences in Salmonella prevalence in subiliac LNs are due to, or influenced by, breed, which in many respects is a proxy for the production system in which the animal is derived. Holstein steers are a by-product of dairy systems, and beef steers are an intended product of commercial beef operations. For the first experiment, Holstein and beef steers originating from the same feedlot and harvested on the same day were sampled. Of the 467 Holstein and 462 beef cattle LNs collected, 62.1% of Holstein and 59.7% of beef cattle samples harbored Salmonella (P = 0.46; qualitative culture), with 51.2 and 48.9% of samples containing quantifiable concentrations (P = 0.49), respectively. The concentration of Salmonella within the LN followed a decreasing trend over the collection period (May to October), averaging 1.4 log CFU/g of LN for both Holstein and beef cattle samples (P = 0.78). In a second experiment, we compared 100% Brahman cattle to their beef cattle counterparts, as we hypothesized that the resistance of Brahman cattle to insects may reduce Salmonella transmission via biting insects. Of the 42 Brahman and 31 beef cattle LNs collected, the concentration of Salmonella within the LN averaged 3.0 log CFU/g for Brahman cattle and 2.9 log CFU/g for beef cattle samples (P = 0.30). Using qualitative culture, we recovered Salmonella from 100% of LNs from Brahman cattle and 97% of beef cattle samples (P = 0.25). Results of this research indicate that the differences observed are not due to breed and are likely a function of age, immune function, or other factors yet to be identified. Understanding which cattle are more likely to harbor Salmonella within LNs will aid in targeting both pre- and postharvest intervention strategies.

Beef cattle welfare in the USA: identification of priorities for future research

This review identifies priorities for beef cattle welfare research in the USA. Based on our professional expertise and synthesis of existing literature, we identify two themes in intensive aspects of beef production: areas where policy-based actions are needed and those where additional research is required. For some topics, considerable research informs best practice, yet gaps remain between scientific knowledge and implementation. For example, many of the risk factors and management strategies to prevent respiratory disease are understood, but only used by a relatively small portion of the industry. This is an animal health issue that will require leadership and discussion to gain widespread adoption of practices that benefit cattle welfare. There is evidence of success when such actions are taken, as illustrated by the recent improvements in handling at US slaughter facilities. Our highest priorities for additional empirical evidence are: the effect of technologies used to either promote growth or manage cattle in feedlots, identification of management risk factors for disease in feedlots, and management decisions about transport (rest stops, feed/water deprivation, climatic conditions, stocking density). Additional research is needed to inform science-based recommendations about environmental features such as dry lying areas (mounds), shade, water and feed, as well as trailer design.

Cross-sectional study examining Salmonella enterica carriage in subiliac lymph nodes of cull and feedlot cattle at harvest

Bovine peripheral lymph nodes (LNs), including subiliac LNs, have been identified as a potential source of human exposure to Salmonella enterica, when adipose trim containing these nodes is incorporated into ground beef. In order to gain a better understanding of the burden of S. enterica in peripheral LNs of feedlot and cull cattle, a cross-sectional study was undertaken in which 3327 subiliac LNs were collected from cattle at harvest in seven plants, located in three geographically distinct regions of the United States. Samples were collected in three seasons: Fall 2010, Winter/Spring 2011, and Summer/Fall 2011. A convenience sample of 76 LNs per day, 2 days per season (approximately 1 month apart), was collected per plant, from carcasses held in the cooler for no less than 24 h. Every 10(th) carcass half on a rail was sampled, in an attempt to avoid oversampling any single cohort of cattle. Median point estimates of S. enterica contamination were generally low (1.3%); however, median Salmonella prevalence was found to be greater in subiliac LNs of feedlot cattle (11.8%) compared to those of cull cattle (0.65%). Enumeration analysis of a subset of 618 feedlot cattle LNs showed that 67% of those harboring S. enterica (97 of 144) did so at concentrations ranging from <0.1 to 1.8 log10 CFU/g, while 33% carried a higher burden of S. enterica, with levels ranging from 1.9 to >3.8 log10 CFU/g. Serotyping of S. enterica isolated identified 24 serotypes, with the majority being Montevideo (44.0%) and Anatum (24.8%). Antimicrobial susceptibility phenotypes were determined for all isolates, and the majority (86.1%) were pansusceptible; however, multidrug-resistant isolates (8.3%) were also occasionally observed. As Salmonella contained within LNs are protected from carcass interventions, research is needed to define opportunities for mitigating the risk of Salmonella contamination in LNs of apparently healthy cattle.

Salmonella diversity and burden in cows on and culled from dairy farms in the Texas High Plains

The objective of this study was to characterize the epidemiology of Salmonella carried by dairy cows culled from herds in the Texas High Plains. Feces were collected from a convenience sample of 706 animals culled from nine dairy farms. In addition, individually paired fecal and hide samples were collected from 70 healthy milking cows on three of the dairies. Samples were cultured for Salmonella using routine methods; isolates were serotyped and subjected to a panel of antimicrobial drugs to determine susceptibility. Salmonella was recovered from 32.6% of culled cows. Whole-herd use of a vaccine containing siderophore receptors and porin proteins was associated (p=0.05) with reduced Salmonella prevalence in that the prevalence among herds that practiced whole-herd vaccination was 8.0% compared to 36.8% among herds that did not use this vaccine. The majority (88.6%) of isolates were pansusceptible or resistant to one drug. Of the 3.1% of isolates resistant to more than four drugs, all were Salmonella Newport and were recovered from one dairy. Various serotypes were recovered from individual fecal and hide samples. Salmonella Montevideo was recovered more frequently (p<0.01) from hide samples, whereas Salmonella Cerro was recovered more frequently (p<0.01) from feces. Salmonella was recovered from at least one cow on all dairies. While our study was not a priori designed to address herd-level factors, we found evidence that the whole-herd use of a siderophore receptor and porin protein-containing vaccine might be a useful aid in the control of Salmonella in groups of cattle. As this is a nonrandomized evaluation of an intervention, other herd-level factors that may be correlated with vaccine use, such as biosecurity, might have been responsible for the observed association.

Modeling preharvest and harvest interventions for Escherichia coli O157 contamination of beef cattle carcasses

Field studies evaluating the effects of multiple concurrent preharvest interventions for Escherichia coli O157 are logistically and economically challenging; however, modeling techniques may provide useful information on these effects while also identifying crucial information gaps that can guide future research. We constructed a risk assessment model with data obtained from a systematic search of scientific literature. Parameter distributions were incorporated into a stochastic Monte Carlo modeling framework to examine the impacts of different combinations of preharvest and harvest interventions for E. coli O157 on the risk of beef carcass contamination. We estimated the risk of E. coli O157 carcass contamination conditional on preharvest fecal prevalence estimates, inclusion of feed additive(s) in the diet, vaccination for E. coli O157, transport and lairage effects, hide intervention(s), and carcass intervention(s). Prevalence parameters for E. coli O157 were assumed to encompass potential effects of concentration; therefore, concentration effects were not specifically evaluated in this study. Sensitivity analyses revealed that fecal prevalence, fecal-to-hide transfer, hide-to-carcass transfer, and carcass intervention efficacy significantly affected the risk of carcass contamination (correlation coefficients of 0.37, 0.56, 0.58, and -0.29, respectively). The results indicated that combinations of preharvest interventions may be particularly important for supplementing harvest interventions during periods of higher variability in fecal shedding prevalence (i.e., summer). Further assessments of the relationships among fecal prevalence and concentration, hide contamination, and subsequent carcass contamination are needed to further define risks and intervention impacts for E. coli O157 contamination of beef.

Evaluation of the effects of a commercially available Salmonella Newport siderophore receptor and porin protein vaccine on fecal shedding of Salmonella bacteria and health and performance of feedlot cattle

OBJECTIVE

To evaluate effects of a Salmonella Newport siderophore receptor and porin protein (SRP) vaccine on cattle health and performance and on prevalence of fecal shedding of Salmonella bacteria in feedlot cattle.

ANIMALS

1,591 beef cattle.

PROCEDURES

Cattle were randomly allocated within a replicate (n = 10 replicates [20 total pens]), administered 2 mL of a Salmonella Newport SRP vaccine (n = 795 cattle) or a placebo (796), and revaccinated approximately 21 days after the first administration. Health and performance data were recorded by trained feedlot personnel who were blinded to treatment. Fresh fecal samples (n = 25) were collected from pen floors on days 0, 60, and 120 and within 24 hours of cattle harvest and were subjected to selective Salmonella culture and serotyping by laboratory personnel who were blinded to treatment. Pen-level mixed models were used to analyze data.

RESULTS

Significant differences in fecal prevalence of Salmonella bacteria or health and performance variables were not detected between vaccinated and control cattle. Salmonella bacteria were recovered from all 10 replicates, and cumulative prevalence estimates ranged from 1.5% to 22%. Overall prevalence of fecal shedding of Salmonella bacteria was 10.2% and 10.9% in vaccinated and control cattle, respectively. Overall morbidity risk was 34.8% for both vaccinated and control cattle. Overall mortality risks were 1.9% and 1.1% for vaccinated and control cattle, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

In this setting, administration of the Salmonella Newport SRP vaccine in feedlot cattle had no effect on fecal prevalence of Salmonella bacteria or cattle health and performance.

Prevalence and persistence of Salmonella in cohorts of feedlot cattle

Our objectives were to determine factors associated with fecal prevalence of Salmonella at feedlot entry and within 24 h of harvest (preharvest), and to assess potential persistence of Salmonella strains within cattle populations. This repeated cross-sectional study followed 5559 beef cattle within 30 feedlot cohorts. Samples (n = 30) of fresh feces were collected from the pen floor of each cohort at feedlot entry and preharvest. Samples were subjected to a selective Salmonella isolation protocol and serotypes were determined for Salmonella isolates. Genetic similarity of a subset of isolates was determined using pulsed-field gel electrophoresis (PFGE). Cattle health and performance data were recorded electronically by feedlot personnel. Cohort-level generalized linear mixed models were used to assess bivariable associations. Fecal prevalence of Salmonella within a cohort at feedlot entry (mean = 64.7%) was not associated with preharvest prevalence (mean = 72.6%). Prevalence at feedlot entry was negatively associated with mean entry weight (p = 0.02). Preharvest prevalence was positively associated with the number of days in the feedlot (p = 0.02), cumulative morbidity (p = 0.01), and cumulative mortality (p = 0.03). We recovered Salmonella isolates with identical PFGE profiles both at feedlot entry and preharvest from 14 cohorts of cattle. Fecal prevalence of Salmonella immediately before harvest may be higher in subsets of the feedlot population, but does not appear to be affected by prevalence at feedlot entry. However, PFGE subtypes of Salmonella appear to persist within and among feedlot cohorts throughout the feeding period.

Environmental dust exposure as a factor contributing to an increase in Escherichia coli O157 and Salmonella populations on cattle hides in feedyards

A study was conducted to determine the impact of exposure to dust in the cattle load-out area in feedyards on pathogen contamination of cattle hides. A total of 250 cattle hides were sampled during summer and fall months, which are associated with elevated prevalence of Escherichia coli O157 in West Texas. Animals were removed from their home pens and restrained in a chute and sampled prior to exposure to dust generated as a result of a simulated loading exercise. The cattle hides were sampled again after exposure to the loading dust to determine total numbers of pathogens on cattle hides on leaving their home pen (before loading) and on cattle hides after exposure to the dust in the loading area. Air and dirt samples from the home pens and the cattle load-out area were also collected. The presence of E. coli O157 and Salmonella was determined in all the samples, and when a positive sample was identified, the total numbers of these bacteria present were enumerated. The total numbers of pathogens increased after dust exposure; Salmonella counts increased from 1.09 log most probable number (MPN)/cm2 to 1.74 log MPN/cm2 after exposure, and E. coli O157 counts increased from 0.80 to 2.35 log MPN/cm2 after sampling. E. coli O157 and Salmonella were recovered from the air samples during dust generation at 6.66 and 11.1%, respectively. Salmonella and E. coli O157 prevalence was not changed and was not associated with the exposure to the dust. Results indicate airborne dust generated as a result of cattle movement and loading could be an important determining factor in total numbers of pathogens recovered on cattle hides.

Potential associations between fecal shedding of Salmonella in feedlot cattle treated for apparent respiratory disease and subsequent adverse health outcomes

A prospective cohort study was used to assess whether Salmonella fecal shedding in commercial feedlot cattle treated with antimicrobials for respiratory disease was associated with subsequent adverse health outcomes. Feces were collected per rectum from cattle that were examined for apparent respiratory disease, had a rectal temperature ≥40 °C, and subsequently received antimicrobial treatment. Salmonella were recovered from 918 (73.7%) of 1 245 fecal samples and weekly prevalence estimates ranged from 49 to 100% over the 3-month study. Genotypic and phenotypic characteristics of Salmonella strains in the population were determined. Serogroup E Salmonella were most common (73.3%), followed by C1 (11.0%), C3 (8.6%), and B (1.1%). Predominant serotypes were Orion (46.5%), Anatum (19.8%), Kentucky (8.7%), Montevideo (7.5%), and Senftenberg (4.9%). Few isolates (36/918) were positive for antimicrobial resistance-associated integron gene intI1. Phenotypic susceptibility was associated with isolate intI1 status. Crude re-pull, re-treatment and case fatality risks were higher for cattle that were Salmonella-positive versus -negative at initial treatment, but not statistically different on multivariable analysis. However, case fatality risk was higher for cattle shedding Group B Salmonella than for cattle shedding other serogroups. Lots (groups) with a higher Salmonella prevalence at first treatment had a higher proportion of mortalities occur in a hospital pen, higher overall re-treatment risks, and were more likely to be sampled later in the study. Results indicate a high prevalence of Salmonella in this population of cattle treated for apparent respiratory disease, but that effects associated with clinical outcomes may depend on the Salmonella strain.

Salmonella enterica burden in harvest-ready cattle populations from the southern high plains of the United States

Our objectives were to quantify the Salmonella enterica burdens in harvest-ready cattle and to identify specific at-risk populations of cattle most likely to harbor multiply resistant S. enterica. Hide swabs were collected in abattoirs from three cohorts of cattle (feedlot origin cattle that had achieved desirable harvest characteristics and dairy- and beef-type cows harvested because of poor productivity). Feces were collected from two cohorts housed in feedlots (cattle that had achieved desirable harvest characteristics and animals identified for salvage recovery because of poor productivity). Facilities were visited on four occasions over a 12-month period. Salmonella enterica isolates were recovered, and organisms were quantified using standard microbiological methodologies. Susceptibility to antimicrobial drugs and serotype were determined for one S. enterica isolate per sample. Salmonella enterica was recovered from 55.6% of 1,681 samples. The prevalences on hides and in feces were 69.6% and 30.3%, respectively. The concentrations of S. enterica organisms averaged (as determined by the most probable number technique) 1.82 log(10)/100 cm(2) of hides and 0.75 log(10)/g of feces. None of the isolates recovered from cattle that had achieved desirable harvest characteristics were resistant to four or more drugs. For isolates recovered from animals with poor productivity characteristics, 6.5% were resistant to four or more drugs. Twenty-two serovars were identified, with the most common being Salmonella enterica serovar Anatum (25.5%), Salmonella enterica serovar Montevideo (22.2%), and Salmonella enterica serovar Cerro (12.5%). High-level resistance, i.e., resistance to four or more drugs, was clustered within a few relatively uncommon serovars. These results demonstrate that even though S. enterica isolates are readily recoverable from harvest-ready cattle, multiply resistant variants are rare and are associated with specific serovars in cattle harvested because of poor productivity characteristics.

Reduction of Escherichia coli O157 and Salmonella in feces and on hides of feedlot cattle using various doses of a direct-fed microbial

In this study, the effectiveness of direct-fed microbials at reducing Escherichia coli O157 and Salmonella in beef cattle was evaluated. Steers (n=240) received one of the following four treatment concentrations: control = lactose carrier only; low = 1 X 10(7) CFU per steer daily Lactobacillus acidophilus NP51; medium = 5 x 10(8) CFU per steer daily L. acidophilus NP51; and high = 1 x 10(9) CFU per steer daily L. acidophilus NP51. Low, medium, and high diets also included 1 x 10(9) CFU per steer Propionibacterium freudenreichii NP24. Feces were collected from each animal at allocation of treatment and found to have no variation (P = 0.54) between cohorts concerning E. coli O157 recovery. Feces and hide swabs were collected at harvest and analyzed for the presence of E. coli O157 by immunomagnetic separation and Salmonella by PCR. No significant dosing effects were detected for E. coli O157 recovery from feces at the medium dose or from hides at the medium and high doses. E. coli O157 was 74% (P < 0.01) and 69% (P < 0.01) less likely to be recovered in feces from animals receiving the high and low diets, respectively, compared with controls. Compared with controls, E. coli O157 was 74% (P = 0.05) less likely to be isolated on hides of cattle receiving the low dose. No significant dosing effects were detected for Salmonella recovery from feces at the medium and low doses or from hides at any doses. Compared with controls, Salmonella was 48% (P = 0.09) less likely to be shed in feces of cattle receiving the high dose. No obvious dose-response of L. acidophilus NP51 on recovery of E. coli O157 or Salmonella was detected in our study.

Preharvest control of Escherichia coli O157 in cattle1

Bovine manure is an important source of Escherichia coli O157 contamination of the environment and foods; therefore, effective interventions targeted at reducing the prevalence and magnitude of fecal E. coli O157 excretion by live cattle (preharvest) are desirable. Preharvest intervention methods can be grouped into 3 categories: 1) exposure reduction strategies, 2) exclusion strategies, and 3) direct antipathogen strategies. Exposure reduction involves environmental management targeted at reducing bovine exposure to E. coli O157 through biosecurity and environmental niche management such as feed and drinking water hygiene, reduced exposure to insects or wildlife, and improved cleanliness of the bedding or pen floor. In the category of exclusion, we group vaccination and dietary modifications such as selection of specific feed components; feeding of prebiotics, probiotics, or both; and supplementation with competitive exclusion cultures to limit proliferation of E. coli O157 in or on exposed animals. Direct antipathogen strategies include treatment with sodium chlorate, antibiotics, bacteriophages, in addition to washing of animals before slaughter. Presently, only 1 preharvest control for E. coli O157 in cattle has been effective and has gained widespread adoption-the feeding probiotic Lactobacillus acidophilus. More research into the effectiveness of parallel and simultaneous application of 1 or more preharvest control strategies, as well as the identification of new pre-harvest control methods, may provide practical means to substantially reduce the incidence of human E. coli O157-related illness by intervening at the farm level.