Determination of Behavioral Changes Associated with Bovine Respiratory Disease in Australian Feedlots.

Accurately identifying bovine respiratory disease is challenging in feedlots, and previous studies suggest behavioral monitoring is important. The study objective was to describe individual differences in physical activity (distance traveled), feeding/watering patterns (proximity to feed and water), and social behavior (average cattle within 3 m) when associated with health status in commercially raised beef cattle during the first 28 days on feed. Data from a previous Australian feedlot study monitoring cattle behavior and associated health outcomes were analyzed. Health status categories were generated for all cattle, and each animal was categorized as known healthy (HLTH), known diseased (SICK), or intermediate/uncertain (INTR). The INTR animals were excluded from the final analysis. Key findings included: differentiation in activity between SICK (n = 138) and HLTH (n = 1508) cattle dependent on time of day, SICK cattle spending more time in water and feeding zones early in the feeding phase (<6 days on feed), SICK cattle spending more time in the water and feeding zone during the overnight hours, and SICK cattle spending more time in groups early in the feeding phase but more time in isolation after the first week on feed. Results illustrate behavioral data were associated with important health outcomes.

Evaluating the effects of antimicrobial drug use on the ecology of antimicrobial resistance and microbial community structure in beef feedlot cattle.

Introduction: Use of antimicrobial drugs (AMDs) in food producing animals has received increasing scrutiny because of concerns about antimicrobial resistance (AMR) that might affect consumers. Previously, investigations regarding AMR have focused largely on phenotypes of selected pathogens and indicator bacteria, such as Salmonella enterica or Escherichia coli. However, genes conferring AMR are known to be distributed and shared throughout microbial communities. The objectives of this study were to employ target-enriched metagenomic sequencing and 16S rRNA gene amplicon sequencing to investigate the effects of AMD use, in the context of other management and environmental factors, on the resistome and microbiome in beef feedlot cattle. Methods: This study leveraged samples collected during a previous longitudinal study of cattle at beef feedlots in Canada. This included fecal samples collected from randomly selected individual cattle, as well as composite-fecal samples from randomly selected pens of cattle. All AMD use was recorded and characterized across different drug classes using animal defined daily dose (ADD) metrics. Results: Overall, fecal resistome composition was dominated by genes conferring resistance to tetracycline and macrolide-lincosamide-streptogramin (MLS) drug classes. The diversity of bacterial phyla was greater early in the feeding period and decreased over time in the feedlot. This decrease in diversity occurred concurrently as the microbiome represented in different individuals and different pens shifted toward a similar composition dominated by Proteobacteria and Firmicutes. Some antimicrobial drug exposures in individuals and groups were associated with explaining a statistically significant proportion of the variance in the resistome, but the amount of variance explained by these important factors was very small (<0.6% variance each), and smaller than associations with other factors measured in this study such as time and feedlot ID. Time in the feedlot was associated with greater changes in the resistome for both individual animals and composite pen-floor samples, although the proportion of the variance associated with this factor was small (2.4% and 1.2%, respectively). Discussion: Results of this study are consistent with other investigations showing that, compared to other factors, AMD exposures did not have strong effects on antimicrobial resistance or the fecal microbial ecology of beef cattle.

Genomic Characterization of Enterococcus hirae From Beef Cattle Feedlots and Associated Environmental Continuum.

Enterococci are commensal bacteria of the gastrointestinal tract of humans, animals, and insects. They are also found in soil, water, and plant ecosystems. The presence of enterococci in human, animal, and environmental settings makes these bacteria ideal candidates to study antimicrobial resistance in the One-Health continuum. This study focused on Enterococcus hirae isolates (n = 4,601) predominantly isolated from beef production systems including bovine feces (n = 4,117, 89.5%), catch-basin water (n = 306, 66.5%), stockpiled bovine manure (n = 24, 0.5%), and natural water sources near feedlots (n = 145, 32%), and a few isolates from urban wastewater (n = 9, 0.2%) denoted as human-associated environmental samples. Antimicrobial susceptibility profiling of a subset (n = 1,319) of E. hirae isolates originating from beef production systems (n = 1,308) showed high resistance to tetracycline (65%) and erythromycin (57%) with 50.4% isolates harboring multi-drug resistance, whereas urban wastewater isolates (n = 9) were resistant to nitrofurantoin (44.5%) and tigecycline (44.5%) followed by linezolid (33.3%). Genes for tetracycline (tetL, M, S/M, and O/32/O) and macrolide resistance erm(B) were frequently found in beef production isolates. Antimicrobial resistance profiles of E. hirae isolates recovered from different environmental settings appeared to reflect the kind of antimicrobial usage in beef and human sectors. Comparative genomic analysis of E. hirae isolates showed an open pan-genome that consisted of 1,427 core genes, 358 soft core genes, 1701 shell genes, and 7,969 cloud genes. Across species comparative genomic analysis conducted on E. hirae, Enterococcus faecalis and Enterococcus faecium genomes revealed that E. hirae had unique genes associated with vitamin production, cellulose, and pectin degradation, traits which may support its adaptation to the bovine digestive tract. E. faecium and E. faecalis more frequently harbored virulence genes associated with biofilm formation, iron transport, and cell adhesion, suggesting niche specificity within these species.

Environmental performance of commercial beef production systems utilizing conventional productivity-enhancing technologies.

The objective of this study was to evaluate the effects of using conventional productivity-enhancing technologies (PETs) with or without other natural PETs on the growth performance, carcass traits, and environmental impacts of feedlot cattle. A total of 768 cross-bred yearling steers (499 ±â€…28.6 kg; n = 384) and heifers (390 ±â€…34.9 kg; n = 384) were offered a barley grain-based basal diet and divided into implanted or non-implanted groups. Steers were then allocated to diets that contained either: (i) no additive (control); natural feed additives including (ii) fibrolytic enzymes (Enz), (iii) essential oil (Oleo), (iv) direct-fed microbial (DFM), (v) DFM + Enz + Oleo combination; conventional feed additives including (vi) Conv (monensin, tylosin, and beta-adrenergic agonists [ßAA]); or Conv with natural feed additives including (vii) Conv + DFM + Enz; (viii) Conv + DFM + Enz + Oleo. Heifers received one of the first three dietary treatments or the following: (iv) probiotic (Citr); (v) Oleo + Citr; (vi) Melengesterol acetate (MGA) + Oleo + ßAA; (vii) Conv (monensin, tylosin, ßAA, and MGA); or (viii) Conv + Oleo (ConvOleo). Data were used to estimate greenhouse gas (GHG) and ammonia (NH3) emissions, as well as land and water use. Implant and Conv-treated cattle exhibited improvements in growth and carcass traits as compared to the other treatments (P < 0.05). Improvements in the performance of Conv-cattle illustrated that replacing conventional feed additives with natural feed additives would increase both the land and water required to satisfy the feed demand of steers and heifers by 7.9% and 10.5%, respectively. Further, GHG emission intensity for steers and heifers increased by 5.8% and 6.7%, and NH3 emission intensity by 4.3% and 6.7%, respectively. Eliminating the use of implants in cattle increased both land and water use by 14.6% and 19.5%, GHG emission intensity by 10.5% and 15.8%, and NH3 emission intensity by 3.4% and 11.0% for heifers and steers, respectively. These results demonstrate that the use of conventional PETs increases animal performance while reducing the environmental impacts of beef production. Restricting use would increase the environmental footprint of beef produced for both domestic and international markets.

Prevalence and Risk Factors Associated With Antimicrobial Resistance in Bacteria Related to Bovine Respiratory Disease-A Broad Cross-Sectional Study of Beef Cattle at Entry Into Canadian Feedlots.

A broad, cross-sectional study of beef cattle at entry into Canadian feedlots investigated the prevalence and epidemiology of antimicrobial resistance (AMR) in Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis, bacterial members of the bovine respiratory disease (BRD) complex. Upon feedlot arrival and before antimicrobials were administered at the feedlot, deep nasopharyngeal swabs were collected from 2,824 feedlot cattle in southern and central Alberta, Canada. Data on the date of feedlot arrival, cattle type (beef, dairy), sex (heifer, bull, steer), weight (kg), age class (calf, yearling), source (ranch direct, auction barn, backgrounding operations), risk of developing BRD (high, low), and weather conditions at arrival (temperature, precipitation, and estimated wind speed) were obtained. Mannheimia haemolytica, P. multocida, and H. somni isolates with multidrug-resistant (MDR) profiles associated with the presence of integrative and conjugative elements were isolated more often from dairy-type than from beef-type cattle. Our results showed that beef-type cattle from backgrounding operations presented higher odds of AMR bacteria as compared to auction-derived calves. Oxytetracycline resistance was the most frequently observed resistance across all Pasteurellaceae species and cattle types. Mycoplasma bovis exhibited high macrolide minimum inhibitory concentrations in both cattle types. Whether these MDR isolates establish and persist within the feedlot environment, requires further evaluation.

Association between computer-aided lung auscultation and treatment failure risk in calves treated for respiratory disease.

The use of computer-aided lung auscultation (CALA, Whisper Veterinary Stethoscope; Merck Animal Health, Madison, New Jersey, USA) is a relatively new approach to assist in confirming the diagnosis of bovine respiratory disease (BRD). For this prospective cohort study at 1 feedlot in the United States, a CALA score was generated for 2726 feeder cattle (calf-fed Holsteins and mixed-breed beef animals) at the time of the first BRD diagnosis and treatment. All cattle were treated according to the same BRD protocol prescribed for that facility and the protocol was not influenced by the CALA score. Data were collected for 120 d after enrollment. In this study, the risk of BRD retreatment and the risk of BRD mortality were each significantly (P < 0.05) associated with the CALA score at the time of first BRD diagnosis and treatment, and those risks increased (numerically and in some cases statistically) as the CALA score increased.

Association entre l'auscultation pulmonaire assistée par ordinateur et le risque d'échec du traitement chez les veaux traités pour une maladie respiratoire. L'utilisation de l'auscultation pulmonaire assistée par ordinateur (CALA, Whisper Veterinary Stethoscope; Merck Animal Health, Madison, New Jersey, USA) est une approche relativement nouvelle pour aider à confirmer le diagnostic de maladie respiratoire bovine (BRD). Pour cette étude de cohorte prospective dans un parc d'engraissement aux États-Unis, un score CALA a été généré pour 2726 bovins d'engraissement (veau Holstein et bovins de race mixte) au moment du premier diagnostic et traitement de la BRD. Tous les bovins ont été traités selon le même protocole BRD prescrit pour ce site et le protocole n'a pas été influencé par le score CALA. Les données ont été collectées pendant 120 jours après l'inscription. Dans cette étude, le risque de retraitement pour BRD et le risque de mortalité associée au BRD étaient chacun significativement (P < 0,05) associés au score CALA au moment du premier diagnostic et traitement BRD, et ces risques augmentaient (numériquement et dans certains cas statistiquement) à mesure que le score CALA augmentait.(Traduit par Dr Serge Messier).

Use of 3-nitrooxypropanol in a commercial feedlot to decrease enteric methane emissions from cattle fed a corn-based finishing diet.

The present study evaluated enteric CH4 production, dry matter (DM) intake (DMI), and rumen fermentation in feedlot cattle supplemented with increasing concentrations of 3-nitrooxypropanol (3-NOP). A total of 100 crossbred steers (body weight, 421 ± 11 kg) was randomly assigned to one of four treatments (n = 25/treatment): control (no 3-NOP) or low (100 mg/kg DM), medium (125 mg/kg DM), and high (150 mg/kg DM) doses of 3-NOP. The study was comprised of 28 d of adaptation followed by three 28-d periods, with CH4 measured for 7 d per period and cattle remaining on their respective diets throughout the 112-d study. Each treatment group was assigned to a pen, with the cattle and diets rotated among pens weekly to allow the animals to access the GreenFeed emission monitoring (GEM) system stationed in one of the pens for CH4 measurement. Measured concentration (mg/kg DM) of 3-NOP in the total diet consumed (basal diet + GEM pellet) was 85.6 for low, 107.6 for medium, and 124.5 for high doses of 3-NOP. There was a treatment × period interaction (P < 0.001) for DMI; compared with control, the DMI was less for the low and high doses in period 1, with no differences thereafter. Compared with control (10.78 g/kg DMI), CH4 yield (g/kg DMI) was decreased (P < 0.001) by 52%, 76%, and 63% for low, medium, and high doses of 3-NOP, respectively. A treatment × period effect (P = 0.048) for CH4 yield indicated that the low dose decreased in efficacy from 59% decrease in periods 1 and 2 to 37% decrease in period 3, while the efficacy of the medium and high doses remained consistent over time. Irrespective of dose, hydrogen emissions increased by 4.9-fold (P < 0.001), and acetate:propionate ratio in rumen fluid decreased (P = 0.045) with 3-NOP supplementation, confirming that other hydrogen-utilizing pathways become more important in the CH4-inhibited rumen. The study indicates that supplementation of corn-based finishing diets with 3-NOP using a medium dose is an effective CH4 mitigation strategy for commercial beef feedlots with a 76% decrease in CH4 yield. Further research is needed to determine the effects of 3-NOP dose on weight gain, feed conversion efficiency, and carcass characteristics of feedlot cattle at a commercial scale.

Feedlot Cattle Antimicrobial Use Surveillance Network: A Canadian Journey.

Antimicrobial drugs are important tools for maintaining human and animal health. Globally, antimicrobial use (AMU) in food-producing animals is under increasing scrutiny due to its potential to promote antimicrobial resistance (AMR). Historically, comprehensive Canadian data related to the types of antimicrobial drugs used, extent of use, common indicators of use and the demographics of the cattle populations receiving antimicrobial drugs have been limited, in part due to segmentation in the cattle industry and fragmentation of the drug distribution system. Appropriate AMU estimates are required to understand AMU practices, to interpret AMR levels and patterns, to meaningfully assess associated public health risks, and to inform stewardship activities. The Canadian beef cattle industry has a long history of collaboration in AMU and AMR research. Prior research projects identified both opportunities and challenges in the collection of AMU data. Cornerstone projects provided insight into the complexity of collecting AMU data in Canada's feedlot sector. This paper will discuss how the lessons learned from past work have contributed to the formation of a Canadian fed-cattle antimicrobial surveillance program that was initiated in 2019. This important surveillance program will allow feedlot cattle AMU to improve management decisions and support AMU best practices in the evolving Canadian AMR landscape.

Multidrug Resistance in Pasteurellaceae Associated With Bovine Respiratory Disease Mortalities in North America From 2011 to 2016.

Multidrug-resistant (MDR; resistance to ≥3 antimicrobial classes) members of the Pasteurellaceae family may compromise the efficacy of therapies used to prevent and treat bovine respiratory disease (BRD) in feedlot cattle. This study examined the prevalence of multidrug resistance in strains of Mannheimia haemolytica and Pasteurella multocida collected from BRD cattle mortalities in North America. Isolates of M. haemolytica (n = 147) and P. multocida (n = 70) spanning 69 Alberta feedlots from 2011 to 2016 and two United States feedlots from 2011 to 2012 were examined for antimicrobial resistance (AMR) in association with integrative and conjugative elements (ICEs). Overall, resistance was high in both bacterial species with an increase in the prevalence of MDR isolates between 2011 and 2016. Resistance to >7 antimicrobial drugs occurred in 31% of M. haemolytica and 83% of P. multocida isolates. Resistance to sulfadimethoxine, trimethoprim/sulfamethoxazole, neomycin, clindamycin oxytetracycline, spectinomycin, tylosin, tilmicosin, and tulathromycin was most common. Although >80% of strains harbored three or more ICE-associated genes, only 12% of M. haemolytica and 77% of P. multocida contained all six, reflecting the diversity of ICEs. There was evidence of clonal spread as P. multocida and M. haemolytica isolates with the same pulsed-field gel electrophoresis profile from the United States in 2011 were isolated in Alberta in 2015-2016. This work highlights that MDR strains of Pasteurellaceae containing ICEs are widespread and may be contributing to BRD therapy failure in feedlot cattle. Given the antimicrobial resistance gene profiles identified, these MDR isolates may be selected for by the use of macrolides, tetracyclines, and/or in-feed supplements containing heavy metals.

Author Correction: Surveillance of Enterococcus spp. reveals distinct species and antimicrobial resistance diversity across a One-Health continuum.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A One Health Comparative Assessment of Antimicrobial Resistance in Generic and Extended-Spectrum Cephalosporin-Resistant Escherichia coli from Beef Production, Sewage and Clinical Settings.

This study aimed to compare antimicrobial resistance (AMR) in extended-spectrum cephalosporin-resistant and generic Escherichia coli from a One Health continuum of the beef production system in Alberta, Canada. A total of 705 extended-spectrum cephalosporin-resistant E. coli (ESCr) were obtained from: cattle feces (CFeces, n = 382), catch basins (CBasins, n = 137), surrounding streams (SStreams, n = 59), beef processing plants (BProcessing, n = 4), municipal sewage (MSewage; n = 98) and human clinical specimens (CHumans, n = 25). Generic isolates (663) included: CFeces (n = 142), CBasins (n = 185), SStreams (n = 81), BProcessing (n = 159) and MSewage (n = 96). All isolates were screened for antimicrobial susceptibility to 9 antimicrobials and two clavulanic acid combinations. In ESCr, oxytetracycline (87.7%), ampicillin (84.4%) and streptomycin (73.8%) resistance phenotypes were the most common, with source influencing AMR prevalence (p < 0.001). In generic E. coli, oxytetracycline (51.1%), streptomycin (22.6%), ampicillin (22.5%) and sulfisoxazole (14.3%) resistance were most common. Overall, 88.8% of ESCr, and 26.7% of generic isolates exhibited multi-drug resistance (MDR). MDR in ESCr was high from all sources: CFeces (97.1%), MSewage (96.9%), CHumans (96%), BProcessing (100%), CBasins (70.5%) and SStreams (61.4%). MDR in generic E. coli was lower with CFeces (45.1%), CBasins (34.6%), SStreams (23.5%), MSewage (13.6%) and BProcessing (10.7%). ESBL phenotypes were confirmed in 24.7% (n = 174) ESCr and 0.6% of generic E. coli. Prevalence of bla genes in ESCr were blaCTXM (30.1%), blaCTXM-1 (21.6%), blaTEM (20%), blaCTXM-9 (7.9%), blaOXA (3.0%), blaCTXM-2 (6.4%), blaSHV (1.4%) and AmpC ß-lactamase blaCMY (81.3%). The lower AMR in ESCr from SStreams and BProcessing and higher AMR in CHumans and CFeces likely reflects antimicrobial use in these environments. Although MDR levels were higher in ESCr as compared to generic E. coli, AMR to the same antimicrobials ranked high in both ESCr and generic E. coli sub-populations. This suggests that both sub-populations reflect similar AMR trends and are equally useful for AMR surveillance. Considering that MDR ESCr MSewage isolates were obtained without enrichment, while those from CFeces were obtained with enrichment, MSewage may serve as a hot spot for MDR emergence and dissemination.

Bovine Respiratory Disease Treatment Failure: Impact and Potential Causes.

Bovine respiratory disease (BRD) is often attributed to complex interactions between the host, pathogen, and the environment. Likewise, many BRD treatment failures result from interactions between the host, pathogen, environment, drug, and drug administrator. Investigating and addressing the underlying causes of BRD treatment failures can improve clinical outcomes and animal welfare of future cases, improve morale of employees, reduce direct costs of dealing with BRD treatment failures, refine antimicrobial prescribing practices, and advance antimicrobial stewardship. This article discusses these interactions and provides guidance to veterinary practitioners on evaluating the success of treatment protocols.

Whole Genome Sequencing Differentiates Presumptive Extended Spectrum Beta-Lactamase Producing Escherichia coli along Segments of the One Health Continuum.

Antimicrobial resistance (AMR) has important implications for the continued use of antibiotics to control infectious diseases in both beef cattle and humans. AMR along the One Health continuum of the beef production system is largely unknown. Here, whole genomes of presumptive extended-spectrum ß-lactamase E. coli (ESBL-EC) from cattle feces (n = 40), feedlot catch basins (n = 42), surrounding streams (n = 21), a beef processing plant (n = 4), municipal sewage (n = 30), and clinical patients (n = 25) are described. ESBL-EC were isolated from ceftriaxone selective plates and subcultured on ampicillin selective plates. Agreement of genotype-phenotype prediction of AMR ranged from 93.2% for ampicillin to 100% for neomycin, trimethoprim/sulfamethoxazole, and enrofloxacin resistance. Overall, ß-lactam (100%; blaEC, blaTEM-1, blaSHV, blaOXA, blaCTX-M-), tetracycline (90.1%; tet(A), tet(B)) and folate synthesis (sul2) antimicrobial resistance genes (ARGs) were most prevalent. The ARGs tet(C), tet(M), tet(32), blaCTX-M-1, blaCTX-M-14, blaOXA-1, dfrA18, dfrA19, catB3, and catB4 were exclusive to human sources, while blaTEM-150, blaSHV-11-12, dfrA12, cmlA1, and cmlA5 were exclusive to beef cattle sources. Frequently encountered virulence factors across all sources included adhesion and type II and III secretion systems, while IncFIB(AP001918) and IncFII plasmids were also common. Specificity and prevalence of ARGs between cattle-sourced and human-sourced presumptive ESBL-EC likely reflect differences in antimicrobial use in cattle and humans. Comparative genomics revealed phylogenetically distinct clusters for isolates from human vs. cattle sources, implying that human infections caused by ESBL-EC in this region might not originate from beef production sources.

Surveillance of Enterococcus spp. reveals distinct species and antimicrobial resistance diversity across a One-Health continuum.

For a One-Health investigation of antimicrobial resistance (AMR) in Enterococcus spp., isolates from humans and beef cattle along with abattoirs, manured fields, natural streams, and wastewater from both urban and cattle feedlot sources were collected over two years. Species identification of Enterococcus revealed distinct associations across the continuum. Of the 8430 isolates collected, Enterococcus faecium and Enterococcus faecalis were the main species in urban wastewater (90%) and clinical human isolates (99%); Enterococcus hirae predominated in cattle (92%) and feedlot catch-basins (60%), whereas natural streams harbored environmental Enterococcus spp. Whole-genome sequencing of E. faecalis (n = 366 isolates) and E. faecium (n = 342 isolates), revealed source clustering of isolates, indicative of distinct adaptation to their respective environments. Phenotypic resistance to tetracyclines and macrolides encoded by tet(M) and erm(B) respectively, was prevalent among Enterococcus spp. regardless of source. For E. faecium from cattle, resistance to ß-lactams and quinolones was observed among 3% and 8% of isolates respectively, compared to 76% and 70% of human clinical isolates. Clinical vancomycin-resistant E. faecium exhibited high rates of multi-drug resistance, with resistance to all ß-lactam, macrolides, and quinolones tested. Differences in the AMR profiles among isolates reflected antimicrobial use practices in each sector of the One-Health continuum.

Investigation of a Reduction in Tylosin on the Prevalence of Liver Abscesses and Antimicrobial Resistance in Enterococci in Feedlot Cattle.

Recent concerns over linkages between antimicrobial resistance in human pathogens and antimicrobial use in livestock have prompted researchers to investigate management strategies that reduce the current reliance on in-feed tylosin to control liver abscesses in feedlot cattle. A total of 7,576 crossbred yearlings were allocated to the study (~253 animals/pen, 10 replicate pens per treatment) and individually randomized to one of three treatments. Tylosin phosphate (11 ppm) was included in-feed (1) for the first 125 days on feed (DOF) (FIRST-78%), (2) for DOF 41 to 161 (LAST-75%), or (3) for the entire feeding period (CON; day 0-161). Fecal composites were collected from the pen floor on days 0, 81, and 160 of the finishing period. Serial dilutions were spread plated for enumeration of enterococci on Bile Esculin Azide (BEA) agar and BEA amended with 8 µg/ml erythromycin. Results indicated that although the proportion of EryR enterococci increased with DOF (P < 0.01), neither treatment (P = 0.34) or treatment × DOF (P = 0.37) affected antimicrobial resistance. Of the 538 isolates, 97% were enterococci, with mixed species isolated early in the feeding period and only Enterococcus hirae isolated at the end. Isolates were most frequently resistant to tylosin (86%), erythromycin (84%), and doxycycline (31%). Macrolide and tetracycline resistant isolates harbored erm(B), msrC, and tet(L), tet(M), tet(O) genes, respectively. Overall, the proportion of EryR enterococci increased (P < 0.05) in all three treatments over the feeding period. Compared to the control cattle, FIRST-78% cattle had more severe (P < 0.05) liver abscesses, while there was a trend (P < 0.08) for this response in LAST-75% cattle. There was no difference (P > 0.05) in total liver abscesses, growth performance, carcass traits, morbidity, or mortality among treatments. These results support the potential to reduce the duration and therefore quantity of tylosin administered to feedlot cattle during the feeding period without impacting animal productivity.

Bovine respiratory disease treatment failure: definition and impact.

Bovine respiratory disease (BRD) treatment failure occurs when animals receiving a treatment regimen for BRD fail to directly return to health, resulting in chronic illness and a requirement for repeated treatments, sale for salvage slaughter, euthanasia or death. BRD treatment failure has both direct and indirect impacts. Direct impacts include costs to manage chronically ill animals, including those associated with BRD relapse treatment; reduced returns from animals sent for salvage slaughter, loss of the initial investment to purchase the animal and feed and other accumulated expenses to death, and costs associated with carcass disposal. Indirect impacts include costs of infrastructure requirements, and negative effects on animal welfare and employee morale.

Corrigendum: Multidrug Resistance in Pasteurellaceae Associated With Bovine Respiratory Disease Mortalities in North America From 2011 to 2016.

[This corrects the article DOI: 10.3389/fmicb.2020.606438.].

Presence and Diversity of Extended-Spectrum Cephalosporin Resistance Among Escherichia coli from Urban Wastewater and Feedlot Cattle in Alberta, Canada.

A recent preliminary study from our group found that extended-spectrum cephalosporin-resistance determinants can be detected in the majority of composite fecal samples collected from Alberta feedlot cattle. Most notably, blaCTX-M genes were detected in 46.5% of samples. Further isolate characterization identified blaCTX-M-15 and blaCTX-M-27, which are widespread in bacteria from humans. We hypothesized that Escherichia coli of human and beef cattle origins share the same pool of blaCTX-M genes. In this study, we aimed to assess and compare the genomic profiles of a larger collection of blaCTX-M-positive E. coli recovered from fecal composite samples from Canadian beef feedlot cattle and human wastewater through whole-genome sequencing. The variants blaCTX-M-55, blaCTX-M-32, blaCTX-M-27, blaCTX-M-15, and blaCTX-M-14 were found in both urban wastewater and cattle fecal isolates. Core genome multilocus sequence typing showed little similarity between the fecal and wastewater isolates. Thus, if the dissemination of genes between urban wastewater and feedlot cattle occurs, it does not appear to be related to the expansion of specific clonal lineages. Further investigations are warranted to assemble and compare plasmids carrying these genes to better understand the modalities and directionality of transfer.

Antimicrobial Use on 36 Beef Feedlots in Western Canada: 2008-2012.

The accurate quantification of antimicrobial use (AMU) in production animals is critical for monitoring trends in exposure to antimicrobial drugs (AMD) over time and examining potential associations with antimicrobial resistance in bacteria. In this study, a census sample of cattle was used to quantify individually-dosed and in-feed AMU as both numbers of animal daily doses (nADD) and total grams of AMD (gAMD) used in cattle placed in 36 western Canadian feedlots between 1-November, 2008 and 31-October, 2012; representing about 21.5% of fed cattle in Canada during that time period. Of the ~2.6 million cattle placed during the 48-month period, 45% were calves, 63% were male, 62% arrived in the fall or winter, and 39% were assessed as high risk for developing bovine respiratory disease (BRD). The proportion of cattle categorized as high risk (HR) for developing BRD was consistent over the 4 years of placement cohorts. Both medically important AMU and ionophore use were summarized but presented separately. A decrease in AMU was observed over the study period, both as nADD and total gAMD, which was primarily driven by a decline in the in-feed administration of tetracyclines. Most in-feed AMU was directed toward prevention and control of liver abscesses. The majority of individually dosed AMU was administered as metaphylaxis to address BRD risks, with category III AMD (medium importance to human medicine as categorized by Health Canada Veterinary Drugs Directorate) used most frequently. Not surprisingly, risk level for developing BRD influenced parenteral AMD exposures, with 95% of cattle categorized as being HR for developing BRD receiving individually dosed AMD compared to 59% of cattle categorized as being low risk (LR) for developing BRD. Cattle categorized as HR for developing BRD were more likely to receive macrolides for BRD metaphylaxis compared to cattle categorized as LR for developing BRD, and cattle categorized as LR for developing BRD were more likely to receive tetracycline for the same purpose. In summary, these data provide an unprecedented representation of AMU in fed cattle in western Canada and direction for future monitoring of AMU in fed cattle.

Calculation of Antimicrobial Use Indicators in Beef Feedlots-Effects of Choice of Metric and Standardized Values.

The potential for antimicrobial use (AMU) to lead to the development of antimicrobial resistant bacteria is an increasingly important priority in human and veterinary medicine. Accurate AMU quantification is essential to assessing the risk of antimicrobial resistance due to AMU. The quantification of AMU in production animals can be difficult, and feedlot beef cattle present a number of unique challenges. This paper presents selected parenteral data from western Canadian beef feedlots to illustrate variations in interpretation of AMU that can arise from the use of different metrics and standards. Specific examples presented compare the number of animal daily doses calculated from a given amount of antimicrobial drug (AMD) using actual and estimated weights of cattle at exposure, dose-based to weight-based indicators representing the same amount of antimicrobial, dose-based AMU indicators using different estimated durations of effect (DOE), and AMU indicators calculated using different standard weights of cattle at exposure. Changing these factors when calculating AMU indicators can have notable influences on the results obtained. Transparency about the methods used to calculate AMU indicators is critical to ensure that comparisons of use among different populations is meaningful and accurate.