Understanding normal microbial populations within areas of the respiratory tract is essential, as variable regional conditions create different niches for microbial flora, and proliferation of commensal microbes likely contributes to clinical respiratory disease. The objective was to describe microbial population variability between respiratory tract locations in healthy horses. Samples were collected from four healthy adult horses by nasopharyngeal lavage (NPL), transtracheal aspirate (TTA), and bronchoalveolar lavage (BAL) of six distinct regions within the lung. Full-length 16S ribosomal DNA sequencing and microbial profiling analysis was performed. There was a large amount of diversity, with over 1797 ASVs identified, reduced to 94 taxa after tip agglomeration and prevalence filtering. Number of taxa and diversity were highly variable across horses, sample types, and BAL locations. Firmicutes, proteobacteria, and actinobacteria were the predominant phyla. There was a significant difference in richness (Chao1, p = 0.02) and phylogenetic diversity (FaithPD, p = 0.01) between NPL, TTA, and BAL. Sample type (p = 0.03) and horse (p = 0.005) contributed significantly to Bray-Curtis compositional diversity, while Weighted Unifrac metric was only affected by simplified sample type (NPL and TTA vs BAL, p = 0.04). There was no significant effect of BAL locations within the lung with alpha or beta diversity statistical tests. Overall findings support diverse microbial populations that were variable between upper and lower respiratory tract locations, but with no apparent difference in microbial populations of the six biogeographic regions of the lung, suggesting that BAL fluid obtained blindly by standard clinical techniques may be sufficient for future studies in healthy horses.

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.

The presented scoping review summarizes the available research evidence and identifies gaps in knowledge for bovine respiratory disease (BRD) prevention. Published literature on BRD from 1990 to April 2021 was searched in online databases, including Medline, CAB Abstracts, Scopus, Biosis, and Searchable Proceedings of Animal Conferences. Citations were systematically evaluated in a three-stage approach using commercial software and summarized in a scoping review format. A total of 265 publications were included in this review with herd/farm management (27.9%) as the most prevalent factors studied, followed by metaphylaxis (24.5%), vaccinations (24.1%), diet formulations, and nutritional supplementations (17.7%), animal characteristics (10.2%), and less common interventions and risk factors (6.4%). A high proportion of studies under herd/farm management (73%), metaphylaxis (86%), vaccinations (70%), animal characteristics (78%), and less common interventions and risk factors (59%) showed either significant effects on reducing BRD morbidity or significant differences of BRD between treatments. However, diet and nutritional supplementations reduced BRD only in 30% of research publications. Most studies on BRD were performed in feedlot populations, and more studies in cow-calf populations are needed. We further suggest meta-analyses on the use of yeast and trace mineral supplementation, and nitric oxide-releasing solution for BRD prevention.

Veterinary diagnostic labs (VDLs) are important service agencies providing essential diagnostic testing for a wide variety of domestic animal species as well as wildlife. They serve key roles in disease monitoring and diagnosis as well as surveillance for diseases of consequence. Of the many roles VDLs serve, one is being a member of the larger team of professionals dealing with the management of the bovine respiratory disease (BRD) complex. VDLs provide a number of services related to the management of BRD. These include disease outbreak investigation, abnormal morbidity characterization, routine monitoring, and biosecurity screening for a variety of infectious agents via methods such as necropsy and histopathology, bacterial culture, antimicrobial sensitivity testing, virus isolation, and serological assays. VDLs continue to look for better methods and assays as instrumentation technology also grows and improves. This is reflected in the growing proliferation of molecular-based assays that provide a high degree of sensitivity and specificity. Professional staff in VDLs work in collaboration with those in academia and private industry to conduct basic research focusing on a different aspect of the BRD complex. VDLs remain a primary source of the varied field-origin infectious agents associated with BRD that are used for research purposes.

It is generally accepted that as bovine respiratory disease (BRD) develops, bacterial pathogens first proliferate in the nasopharynx and then colonize the lungs, leading to bronchopneumonia. However, such temporal changes have never been definitively demonstrated. Therefore, the objective was to describe the progression of the nasopharyngeal and tracheal bacterial microbiotas of feedlot cattle during development of BRD. Nasopharyngeal swabs and tracheal wash samples were collected from 24 heifers over 20 d after arrival at a feedlot. Heifers were assessed daily and sampled based on reticulo-rumen/rectal temperatures and development of clinical signs of BRD. The study end point for each heifer was either at BRD treatment (BRD group; n = 15) or day 20 if the heifer remained healthy or did not meet BRD treatment criteria (TOL group; n = 9). Total DNA was extracted from each sample and the 16S rRNA gene (V3-V4) sequenced. Alpha and beta diversity were compared between BRD-TOL groups and sampling locations over time. There were no common patterns of change over time in composition or diversity of either the nasopharyngeal or tracheal bacterial microbiotas of cattle that developed BRD. Health status affected bacterial composition (R2 = 0.043; < 0.001), though this effect was low compared to variation among individual animals (R2 = 0.335; < 0.001) and effects of days on feed (R2 = 0.082; < 0.001). Specific bacterial taxa (Moraxella and Mycoplasma dispar) nevertheless appeared to have a potential role in respiratory health.

Bovine Respiratory Disease (BRD) is a major threat to animal health and welfare in the cattle industry. Strains of Mannheimia haemolytica (Mh) that are resistant to multiple classes of antimicrobials are becoming a major concern in the beef industry, as the frequency of isolation of these strains has been increasing. Mobile genetic elements, such as integrative conjugative elements (ICE), are frequently implicated in this rapid increase in multi-drug resistance. The objectives of the current study were to determine the genetic relationship between the isolates collected at arrival before metaphylaxis and at revaccination after metaphylaxis, to identify which resistance genes might be present in these isolates, and to determine if they were carried on an ICE. Twenty calves culture positive for Mh at arrival and revaccination were identified, and a total of 48 isolates with unique susceptibility profiles (26 from arrival, and 22 from revaccination) were submitted for whole-genome sequencing (WGS). A phylogenetic tree was constructed, showing the arrival isolates falling into four clades, and all revaccination isolates within one clade. All revaccination isolates, and one arrival isolate, were positive for the presence of an ICE. Three different ICEs with resistance gene modules were identified. The resistance genes aphA1, strA, strB, sul2, floR, erm42, tetH/R, aadB, aadA25, blaOXA-2, msrE, mphE were all located within an ICE. The gene bla-ROB1 was also present in the isolates, but was not located within an ICE.

The role of the respiratory bacterial microbiota in the pathogenesis of bovine respiratory disease (BRD) is still not well defined, limiting our understanding of the disease. Specifically, there is no information on the nasopharyngeal bacterial microbiota of cattle raised without antimicrobials. The objective was to characterize and compare the nasopharyngeal bacterial microbiota in feedlot cattle raised without antimicrobials that were healthy or diagnosed with BRD. Newly-received feedlot cattle (arrival bodyweight ± SD = 218 ± 37 kg) with BRD (n = 82) and pen-matched controls (n = 82) were clinically examined and sampled by deep nasopharyngeal swab (DNS). DNA was extracted from each DNS and the 16S rRNA gene (V4) was sequenced. Alpha and beta diversity were compared between health groups and among 3 days-on-feed (DOF) groups (group A = 3-12 DOF; group B = 13-20 DOF; group C = 21-44 DOF). Observed species richness was lower (P = 0.031) in cattle with BRD compared to healthy ones. Both health status (P = 0.007) and DOF groups (P < 0.001) were sources of variation in microbiota composition. Differences between health groups were driven by multiple sequence variants, including Mycoplasma bovis, Histophilus somni, and several Moraxella spp. Notably, M. bovis was more frequently identified in cattle with BRD. M. bovis identification was also higher in cattle sampled at later DOF. The increased identification of M. bovis in cattle with BRD reaffirms a potentially significant role for this bacterium in respiratory health.

BACKGROUND: Severity of lung lesions quantified by thoracic ultrasonography (TUS) at time of bronchopneumonia (BP) diagnosis predicted death among steers not treated for this condition. Further research is needed to confirm that lung lesions detected by TUS can be associated with negative outcomes in cattle with BP that subsequently were treated.
OBJECTIVE: To quantify the effects on relapse rate and average daily gain (ADG) of lung lesions detected by TUS at first BP diagnosis in feedlot cattle.
METHODS: Prospective cohort of mixed beef-breed steers (n = 93; 243 ± 36 kg) and heifers (n = 51; 227 ± 42 kg) with BP at 4 feedlots.
METHODS: Thoracic ultrasonography was performed by the same clinician and 16-second TUS videos were evaluated offline for maximal depth and area of lung consolidation, maximum number of comet tails, and maximal depth of pleural fluid. Individual ADG was calculated between 1 and 120 days after arrival. Effects of lesions on relapse rate and ADG were investigated using mixed regression models.
RESULTS: Maximal depth of lung consolidation was associated with a higher risk of relapse (odds ratio [OR], 1.337/cm; 95% confidence interval [CI], 1.042-1.714) and lower ADG (- 34 g/cm; -64 to -4). Maximal area of lung consolidation also was associated with a higher relapse risk (OR, 1.052/cm2 ; 1.009-1.097) but not with ADG. Comet tails and pleural fluid were not associated with risk of relapse or ADG.
CONCLUSIONS: Quantifying maximal depth and area of lung consolidation by TUS at first BP diagnosis can provide useful prognostic information in feedlot cattle.

Background: Mannheimia haemolytica is the major bacterial infectious agent of bovine respiratory disease complex and causes severe morbidity and mortality during lung infections. M. haemolytica secretes a protein leukotoxin (Lkt) that binds to the CD18 receptor on leukocytes, initiates lysis, induces inflammation, and causes acute fibrinous bronchopneumonia. Lkt binds the 22-amino acid CD18 signal peptide domain, which remains uncleaved in ruminant species. Our aim was to identify missense variation in the bovine CD18 signal peptide and measure the effects on Lkt binding. Methods: Missense variants in the integrin beta 2 gene ( ITGB2) encoding CD18 were identified by whole genome sequencing of 96 cattle from 19 breeds, and targeted Sanger sequencing of 1238 cattle from 46 breeds. The ability of different CD18 signal peptide variants to bind Lkt was evaluated by preincubating the toxin with synthetic peptides and applying the mixture to susceptible bovine cell cultures in cytotoxicity-blocking assays. Results: We identified 14 missense variants encoded on 15 predicted haplotypes, including a rare signal peptide variant with a cysteine at position 5 (C 5) instead of arginine (R 5). Preincubating Lkt with synthetic signal peptides with C 5 blocked cytotoxicity significantly better than those with R 5. The most potent synthetic peptide (C 5PQLLLLAGLLA) had 30-fold more binding activity compared to that with R 5. Conclusions: The results suggest that missense variants in the CD18 signal peptide affect Lkt binding, and animals carrying the C 5 allele may be more susceptible to the effects of Lkt. The results also identify a potent class of non-antibiotic Lkt inhibitors that could potentially protect cattle from cytotoxic effects during acute lung infections.

Shipping Fever is a transport associated syndrome seen in equids and bovines transported during long distances. The microbial profile and clinical signs vary between species, and in horses it is characterized by pharyngeal commensal bacteria and aerosolized particulate matter invading the lower airway due to compromised mucocillary clearance mechanisms during transports. This leads to pyrexia, pulmonary parenchymal disease, inappetence, and in severe cases pleuropneumonia. It has been shown that the incidence of transport-related pyrexia in horses increases with travel time and distance, however, this incidence rate has been expressed as the cumulative number of horses showing pyrexia with the length of travel time during road transport (cumulative percentage), which does not accurately reflect the actual temperature fluctuations and their patterns in relation to shipping fever. This study aims to demonstrate the individual fluctuations of body temperature variations during transport, particularly febrile changes. 53 Anglo-Arab and Thoroughbred horses aged 23-30 months were transported by road over different distances and durations (36-61 h; 1,492-2,921 km) in 3 investigations carried out in the spring and mid-summer in the northern hemisphere. The results showed that the incidence of fever (characterized by rectal temperature >38.6°C) was highest from 20 to 49 h after the start of transport. Clinical signs of shipping fever was observed in 25 of the 53 horses (47.2%), of which 10 horses (18.9%) exhibited fever at the end of transportation and 15 horses (28.3%) did not. This showed that horses that develop shipping fever do not necessarily present with fever at the end of transportation. Necropsy of 20 horses performed immediately after transportation suggested that transport induced pneumonia, contributed to the onset of pyrexia. This finding supports the suggestion that measuring body temperature upon arrival to determine the presence or absence of shipping fever could result in missed diagnoses for some horses with subclinical pneumonia, and that taking multiple temperature measurements at intervals from 20 h of transportation is a simple method for not missing horses with subclinical pneumonia.