Comparison of Pasteurella spp. simultaneously isolated from nasal and transtracheal swabs from cattle with clinical signs of bovine respiratory disease

Variation in Pen-Level Prevalence of BRD Bacterial Pathogens and Antimicrobial Resistance Following Feedlot Arrival in Beef Calves

Antimicrobials are crucial for treating bovine respiratory disease (BRD) in beef feedlots. Evidence is needed to support antimicrobial use (AMU) decisions, particularly in the early part of the feeding period when BRD risk is highest. The study objective was to describe changes in prevalence and antimicrobial susceptibility of BRD bacterial pathogens at feedlot processing (1 day on feed (1DOF)), 12 days later (13DOF), and for a subset at 36DOF following metaphylactic antimicrobial treatment. Mixed-origin steer calves (n = 1599) from Western Canada were managed as 16 pens of 100 calves, receiving either tulathromycin (n = 1199) or oxytetracycline (n = 400) at arrival. Deep nasopharyngeal swabs collected at all time points underwent culture and antimicrobial susceptibility testing (AST). Variability in the pen-level prevalence of bacteria and antimicrobial susceptibility profiles were observed over time, between years, and metaphylaxis options. Susceptibility to most antimicrobials was high, but resistance increased from 1DOF to 13DOF, especially for tetracyclines and macrolides. Simulation results suggested that sampling 20 to 30 calves per pen of 200 reflected the relative pen-level prevalence of the culture and AST outcomes of interest. Pen-level assessment of antimicrobial resistance early in the feeding period can inform the evaluation of AMU protocols and surveillance efforts and support antimicrobial stewardship in animal agriculture.

Nasopharyngeal Bacterial Prevalence and Microbial Diversity at First Treatment for Bovine Respiratory Disease (BRD) and Its Associations with Health and Mortality Outcomes in Feedyard Cattle

Bovine respiratory disease (BRD) is an economically important disease in feedyards influencing both animal welfare and antimicrobial utilization. Major pathogens associated with BRD have been identified in previous research, but little information is available on the relationship between nasopharyngeal microbiota and health outcomes. The objective of this study was to identify potential associations between nasopharyngeal microbiota and antimicrobial resistance patterns of clinical cases that lived or died compared to non-diseased controls. Enrolled animals were subdivided based on clinical disease status and case outcome (subsequent mortality). Deep nasopharyngeal swabs were collected on enrolled animals and submitted for bacterial isolation, antimicrobial susceptibility determination, and metagenomics analysis. Enrolled cattle were represented in three groups: animals at first treatment for BRD that subsequently died (BRDM, n = 9), animals at first treatment for BRD that subsequently lived (BRDL, n = 15), and animals that were never treated for BRD during the feeding phase (CONT, n = 11). Antimicrobial resistance patterns for Pasteurella multocida illustrated cattle in each outcome category had isolates that were pan-susceptible or only showed resistance to oxytetracycline. The relative abundance of species and genera illustrated few differences among the three outcomes. Higher alpha diversity was identified in BRDL compared to CONT at the species level, and both BRDL and BRDM showed increased alpha diversity compared to CONT at the general level. Overall, this work illustrated nasopharyngeal microbiota showed relatively few differences among BRD cases that lived or died compared to animals without BRD.

Does swab type matter? Comparing methods for Mannheimia haemolytica recovery and upper respiratory microbiome characterization in feedlot cattle

Background

Bovine respiratory disease (BRD) is caused by interactions among host, environment, and pathogens. One standard method for antemortem pathogen identification in cattle with BRD is deep-guarded nasopharyngeal swabbing, which is challenging, costly, and waste generating. The objective was to compare the ability to recover Mannheimia haemolytica and compare microbial community structure using 29.5 inch (74.9 cm) deep-guarded nasopharyngeal swabs, 16 inch (40.6 cm) unguarded proctology swabs, or 6 inch (15.2 cm) unguarded nasal swabs when characterized using culture, real time-qPCR, and 16S rRNA gene sequencing. Samples for aerobic culture, qPCR, and 16S rRNA gene sequencing were collected from the upper respiratory tract of cattle 2 weeks after feedlot arrival.

Results

There was high concordance of culture and qPCR results for all swab types (results for 77% and 81% of sampled animals completely across all 3 swab types for culture and qPCR respectively). Microbial communities were highly similar among samples collected with different swab types, and differences identified relative to treatment for BRD were also similar. Positive qPCR results for M. haemolytica were highly concordant (81% agreed completely), but samples collected by deep-guarded swabbing had lower amounts of Mh DNA identified (Kruskal–Wallis analysis of variance on ranks, P < 0.05; Dunn-test for pairwise comparison with Benjamini–Hochberg correction, P < 0.05) and lower frequency of positive compared to nasal and proctology swabs (McNemar’s Chi-square test, P < 0.05).

Conclusions

Though differences existed among different types of swabs collected from individual cattle, nasal swabs and proctology swabs offer comparable results to deep-guarded nasopharyngeal swabs when identifying and characterizing M. haemolytica by culture, 16S rRNA gene sequencing, and qPCR.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-022-00197-6.

Limitations of bacterial culture, viral PCR, and tulathromycin susceptibility from upper respiratory tract samples in predicting clinical outcome of tulathromycin control or treatment of bovine respiratory disease in high-risk feeder heifers

A cross-sectional prospective cohort study including 1026 heifers administered tulathromycin due to high risk of clinical signs of bovine respiratory disease (BRD), measured poor association between BRD clinical outcomes and results of bacterial culture and tulathromycin susceptibility from BRD isolates of deep nasopharyngeal swabs (DNS) and adequate association with viral polymerase chain reaction (PCR) results from nasal swabs. Isolation rates from DNS collected on day-0 and at 1st BRD-treatment respectively were: Mannheimia haemolytica (10.9% & 34.1%); Pasteurella multocida (10.4% & 7.4%); Mycoplasma bovis (1.0% & 36.6%); and Histophilus somni (0.7% & 6.3%). Prevalence of BRD viral nucleic acid on nasal swabs collected exclusively at 1st BRD-treatment were: bovine parainfluenza virus type-3 (bPIV-3) 34.1%; bovine viral diarrhea virus (BVDV) 26.3%; bovine herpes virus type-1 (BHV-1) 10.8%; and bovine respiratory syncytial virus (BRSV) 54.1%. Increased relative risk, at 95% confidence intervals, of 1st BRD-treatment failure was associated with positive viral PCR results: BVDV 1.39 (1.17-1.66), bPIV-3 1.26 (1.06-1.51), BHV-1 1.52 (1.25-1.83), and BRSV 1.35 (1.11-1.63) from nasal swabs collected at 1st BRD-treatment and culture of M. haemolytica 1.23 (1.00-1.51) from DNS collected at day-0. However, in this population of high-risk feeder heifers, the predictive values of susceptible and resistant isolates had inadequate association with BRD clinical outcome. These results indicate, that using tulathromycin susceptibility testing of isolates of M. haemolytica or P. multocida from DNS collected on arrival or at 1st BRD-treatment to evaluate tulathromycin clinical efficacy, is unreliable.

Prevalence of three Mycoplasma sp. by multiplex PCR in cattle with and without respiratory disease in central Mexico

This study aimed to identify Mycoplasma bovis, Myc. dispar, and Myc. bovirhinis, which are involved in bovine respiratory disease through a multiplex PCR as an alternative to culture's features that hamper Mycoplasma isolation. Nasal swabs were taken from 335 cattle with and without respiratory disease background (RDB) from dairy herds in the central region of Mexico. Each sample was divided in two; the first part was processed for the direct DNA extraction of the nasal swab and the second for Mycoplasma isolation, culture, and then the multiplex PCR was performed. In the nasal swabs, Myc. bovis was identified in 21.1%; Myc. dispar, in 11.8%; and Myc. bovirhinis, in 10.8% in cattle with RDB. Isolates were identified as Myc. bovis, 20.1%; Myc. dispar, 11.8%; and Myc. bovirhinis, 6.1%. There is a strong correlation between the presence of Mycoplasma identified by PCR and the clinical history of the disease (ρ < 0.0000). In animals without RDB, Myc. bovirhinis was the only species detected in 6.1% of the samples processed directly for multiplex PCR, and in 2% of the isolates. There is an excellent correlation (kappa 0.803) between the isolation and the 16S PCR and a high correlation (kappa 0.75) between the isolation and the multiplex PCR. Therefore, we conclude that the PCR multiplex test is highly sensitive and may be used for the diagnosis and surveillance of the three species in biological samples and mycoplasma isolates.

Prevalence and antimicrobial resistance of opportunistic pathogens associated with bovine respiratory disease isolated from nasopharyngeal swabs of veal calves in Switzerland

The composition of the bacterial flora in the calf nasopharynx might influence the risk of bovine respiratory disease (BRD). The aims of the present study were, firstly, to investigate the prevalence of bacteria potentially involved in BRD in the nasopharynx of veal calves and to identify associated risk factors for their presence, and, secondly, to provide data on antimicrobial resistance levels in these bacteria. Deep nasopharyngeal swabs were collected from veal calves on 12 Swiss farms over a period of one year by non-random, but systematic sampling for isolation of Pasteurellaceae and Mycoplasma (M.) bovis and dispar. Associations of potential risk factors with occurrence of these bacteria were tested in multivariable mixed logistic regression analyses, based on information gained from extensive questionnaires completed with the farmers. Antimicrobial susceptibility testing was performed for Pasteurellaceae by broth microdilution method to obtain minimal inhibitory concentrations (MIC). Pasteurellaceae, including Pasteurella (P.) multocida, Mannheimia (M.) haemolytica, Bisgaard Taxon 39 and Histophilus (H.) somni, were almost twice as prevalent as M. bovis and dispar in this study. Continuous stocking was a risk factor for the presence of Pasteurellaceae, especially when calves originated from more than six suppliers. In young calves (≤ 91 days), feeding of California Mastitis Test (CMT) positive milk was an additional risk factor for the presence of Pasteurellaceae whereas transport of calves by farmers and livestock traders (as opposed to transport only by farmers) increased the risk in older calves (> 91 days). Risk factors for the presence of M. bovis/dispar were higher number of calves per drinking nipple in young calves, and no access to an outside pen and feeding of CMT positive milk in older calves, respectively. While further research will have to investigate the observed associations in more detail, this suggests that management can play an important role in the prevalence of nasopharyngeal bacteria with a potential subsequent involvement in BRD. Antimicrobial resistance differed between the three bacterial species tested in this study and was highest to oxytetracycline and spectinomycin in P. multocida, oxytetracycline and penicillin in M. haemolytica, and ampicillin and penicillin in H. somni. Only two European VetCAST breakpoints (for florfenicol in P. multocida and M. haemolytica) have been published to date, matching the MIC distribution of the present isolate populations well, in contrast to certain commonly applied American Clinical and Laboratory Institute interpretive criteria. This highlights the potential for further refinement of clinical breakpoints in veterinary medicine.

Structural characteristics of circulating immune complexes in calves with bronchopneumonia: Impact on the quiescent leukocytes

Calf bronchopneumonia is accompanied by increased level of circulating immune complexes (CIC), and we analysed size, and protein and lipid constituents of these CIC with an attempt to elucidate the connection between the CIC structural properties and their capacity to modulate leukocyte function. CIC of heathy calves (CIC_H) and calves with naturally occurring bronchopneumonia (CIC_D) were isolated by PEG precipitation and analysed by electrophoresis and chromatography. The predominant CIC proteins were IgG, albumin, and transferrin. Affinity isolated serum and CIC IgG coprecipitated several proteins, but only 75 and 80 kDa proteins bound CIC IgG, exclusively. 60 and 65 kDa proteins co-precipitated with CIC_D IgG, unlike CIC_H IgG. In both CIC_H and CIC_D, oleic acid-containing phospholipids predominated. In CIC_D, the content of oleic and vaccenic acid was higher than in CIC_H, while myristic, palmitic, stearic, linoleic and arachidonic acid showed lower content. Dynamic light scattering displayed difference in particle size distribution between CIC_H and CIC_D; 1280 nm large particles were present only in CIC_D. The effect of CIC_H and CIC_D on mononuclear cells (MNC) and granulocytes was analysed in vitro. CIC_H and CIC_D, with slight difference in intensity, stimulate MNC apoptosis, promote cell cycle arrest of unstimulated MNC, and cell cycle progression of PHA stimulated MNC. Both CIC reduced granulocyte apoptosis after 24 h while after 48 h this effect was detected for CIC_D only. These results indicate that structural differences of CIC_H and CIC_D might interfere with the CIC functional capacity, which we consider important for evaluation of CIC immunoregulatory function.

Insights into Pasteurellaceae carriage dynamics in the nasal passages of healthy beef calves

We investigated three bovine respiratory pathobionts in healthy cattle using qPCR optimised and validated to quantify Histophilus somni, Mannheimia haemolytica and Pasteurella multocida over a wide dynamic range. A longitudinal study was conducted to investigate the carriage and density of these bacteria in the nasal passages of healthy beef calves (N = 60) housed over winter in an experimental farm setting. The three pathobiont species exhibited remarkably different carriage rates and density profiles. At housing, high carriage rates were observed for P. multocida (95%), and H. somni (75%), while fewer calves were positive for M. haemolytica (13%). Carriage rates for all three bacterial species declined over the 75-day study, but not all individuals became colonised despite sharing of environment and airspace. Colonisation patterns ranged from continuous to intermittent and were different among pathobiont species. Interval-censored exponential survival models estimated the median duration of H. somni and P. multocida carriage at 14.8 (CI_95%: 10.6–20.9) and 55.5 (CI_95%: 43.3–71.3) days respectively, and found higher density P. multocida carriage was associated with slower clearance (p = 0.036). This work offers insights into the dynamics of pathobiont carriage and provides a potential platform for further data collection and modelling studies.

Antimicrobial Susceptibility Testing of Bacteria of Veterinary Origin

Antimicrobial susceptibility testing is an essential tool to the veterinarian for selecting the most appropriate agent for treatment of bacterial diseases of animals. The availability of well-defined methods that incorporate the necessary quality controls coupled to clinical outcome data is foundational in providing relevant test results for clinical decisions. Since 1993, the Clinical Laboratory and Standards Institute (CLSI) Subcommittee on Veterinary Antimicrobial Susceptibility Testing (VAST) has developed specific test methods and interpretive criteria for veterinary pathogens. This information has allowed for veterinarians to more effectively treat animal diseases thereby protecting both animal welfare and human food security. Moreover, the availability of standardized test methods for veterinary pathogens has allowed for the development of antimicrobial surveillance programs to detect the emergence of resistance among veterinary pathogens. Future work by the VAST and other groups will be critical to expanding the current test methods and interpretive criteria to more pathogen-antibacterial combinations, as well as, the incorporation of genomic information for routine antimicrobial susceptibility testing in the veterinary diagnostic laboratory.

Prevalence and antimicrobial susceptibility of Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni isolated from the lower respiratory tract of healthy feedlot cattle and those diagnosed with bovine respiratory disease

Current information on prevalence and antimicrobial resistance (AMR) of bacterial respiratory pathogens is crucial to guide antimicrobial choice for control and treatment of bovine respiratory disease (BRD). The objectives were to describe the prevalence of three BRD-associated bacteria (Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni) in the lower airways of feedlot cattle, and to analyze AMR in these bacteria. Cattle with (n=210) and without (n=107) BRD were sampled by trans-tracheal aspiration at four feedlots (Nov. 15-Jan. 16). These cattle had received 2.5mg/kg of tulathromycin on arrival at the feedlot for BRD control and two in-feed pulses of chlortetracycline (5g/animal/day for 5days) within the first 21days on feed to prevent histophilosis. Bacteria were detected by culture and AMR was tested by microdilution. Pasteurella multocida was the most frequent bacterium isolated in cattle with BRD (54.8%), followed by M. haemolytica (30.5%) and H. somni (22.9%). Compared to those with BRD, healthy cattle were less likely to be positive for P. multocida (OR=0.27), M. haemolytica (OR=0.32), or H. somni (OR=0.25). There were high levels of resistance (>70%) against tulathromycin and oxytetracycline in M. haemolytica and P. multocida isolates and high levels of resistance against oxytetracycline (67%) and penicillin (52%) in H. somni isolates. None or few isolates were resistant to florfenicol, enrofloxacin and ceftiofur. The high prevalence of resistance against tulathromycin and oxytetracycline suggests that these antimicrobials should not be repeatedly used for both control and treatment of BRD and/or histophilosis.

Serum proteins and lipids in mild form of calf bronchopneumonia: candidates for reliable biomarkers

Calf bronchopneumonia is complex multifactorial disease and for its accurate diagnosis and therapy, besides clinical examination, microbiologic, hematologic and biochemical analyses could be necessary. In general, additional analyses are not implemented, mainly because the disease biomarkers are not defined.

To establish which analysis might be useful for determining the severity of the disease, we analyzed 23 three-month old calves with mild clinical signs of bronchopneumonia and 15 age-matched healthy calves. Pasteurella multocida was isolated from deep nasal swabs of diseased calves. Peripheral blood erythrocyte and leukocyte count of bronchopneumonic and healthy calves showed no difference. Serum proteins, lipoproteins and lipids were analyzed with spectrophotometry, agarose gel electrophoresis, non-reducing SDS-PAGE, gel zymography, and thin-layer chromatography. The bronchopneumonic calves had an increased level of circulating immune complexes and α globulins, which contain some of the positive acute phase proteins. In diseased calves the increased concentration of total γ globulins (IgG), due to an increased concentration of anionic γ globulins (predominately IgG1), was detected. The increased concentration of anionic γ globulins followed by increased concentration of transferrin (negative acute phase protein) and HDL cholesterol, decreased concentration of LDL-cholesterol, unchanged activity of matrix metalloproteases and leukocyte counts might reflect the obvious absence of generalized inflammation. A positive correlation was found between the acquired results and the appearance of mild clinical signs. Therefore, we believe that the parameters analyzed in the peripheral blood could be applied as reliable disease markers to distinguish between severe (inflammatory) and mild forms of calf bronchopneumonia and to predict a better outcome for these calves.

Agreement Among 4 Sampling Methods to Identify Respiratory Pathogens in Dairy Calves with Acute Bovine Respiratory Disease

Background

Four sampling techniques commonly are used for antemortem identification of pathogens from cattle with bovine respiratory disease (BRD): the nasal swab (NS), guarded nasopharyngeal swab (NPS), bronchoalveolar lavage (BAL), and transtracheal wash (TTW). Agreement among these methods has not been well characterized.

Objective

To evaluate agreement among TTW and NS, NPS, or BAL for identification of viral and bacterial pathogens in dairy calves with BRD.

Animals

One hundred dairy calves with naturally acquired BRD.

Methods

Calves were sampled by all 4 methods. Viral agents were identified by real‐time RT‐PCR, bacteria were identified by aerobic culture, and Mycoplasma bovis (M. bovis) isolates were speciated by PCR. Agreement among TTW and NS, NPS, or BAL was evaluated by calculating the kappa statistic and percent positive agreement. McNemar's exact test was used to compare the proportions of positive results.

Results

Agreement among TTW and NS, TTW and NPS, and TTW and BAL, was very good for identification of P. multocida, M. haemolytica, and M. bovis. For bovine respiratory syncytial virus (BRSV), agreement with TTW was moderate for NS, good for NPS, and very good for BAL. For bovine coronavirus (BCV), agreement with TTW was moderate for NS and NPS, and good for BAL. McNemar's test was significant only for BCV, indicating that for this pathogen the proportion of positive results from NS and NPS could not be considered comparable to TTW.

Conclusions and Clinical Importance

This study provides guidance for veterinarians selecting diagnostic tests for antemortem identification of pathogens associated with BRD.

Health and growth of Finnish beef calves and the relation to acute phase response

Healthy, thriving calves are essential for beef calf production. We studied the health status and factors associated with the growth of beef calves in six cow-calf herds during the first month of the calves' lives and at weaning age (200 days). The six herds were visited three times, when calves were approximately 3 days, 16 days and 30 days of age. On each visit calves (n=37) were clinically examined, weighed or measured, blood samples were collected, faecal samples obtained and deep nasopharyngeal swabs were taken. Each blood sample was analysed for acute phase proteins (haptoglobin, serum amyloid-A, fibrinogen), total proteins and albumin, the faecal sample for intestinal tract pathogens (rotavirus, bovine coronavirus, enterotoxigenic Escherichia coli and Salmonella, oocysts of Eimeria coccidia and Cryptosporidium, and nematode eggs), and the nasopharyngeal swab for respiratory tract pathogens (bovine coronavirus (BCV), respiratory syncytial virus (RSV), bacteria and mycoplasma). Clinical diagnosis of respiratory tract disease, diarrhoea or umbilical disease was set at 15.0% for all the three consecutive examinations combined (n=107), but only few pathogens were detected from the samples. The increased levels of acute phase proteins were neither associated with any of the diseases nor with the pathogens. Random intercept linear models were used to explore factors affecting early (3-30 days) and long-term (3-200 days) growth, showing that calves with elevated serum amyloid-A concentrations at the age of 16 days had lower long-term growth. Increased albumin concentration at 30 days of age and higher parity of the dam increased early-term growth. The lack of association between a disease and the acute phase protein may stem from the low disease prevalence in the beef calves examined. The measurement of acute phase proteins of a young calf can help identify animals with possible future growth deficiencies, although the mechanisms through which the association between acute phase proteins and growth has yet to be explained.

Characterization of Mannheimia haemolytica in beef calves via nasopharyngeal culture and pulsed-field gel electrophoresis

Mannheimia haemolytica is a major bacterial component of bovine respiratory disease (BRD); unfortunately, very little is known about M. haemolytica transmission dynamics among cattle. Identifying potential variation in M. haemolytica populations over time and induction of nasopharyngeal colonization and subsequent shedding are 2 areas where knowledge is lacking. In our study, 2 separate loads of 20 mixed-origin, male calves were purchased through an order buyer on different dates. Deep nasopharyngeal cultures (NPC) were performed on all calves on arrival and, if M. haemolytica-negative, a second screening culture was obtained. Calves that were negative on 2 initial NPCs (NEG; n = 4) were subsequently challenged with a previously isolated field strain of M. haemolytica in both the upper and lower respiratory tract, individually housed, and then monitored for M. haemolytica shedding via NPCs at 0.5, 1, 3, 5, 7, and 9 days postchallenge. Naturally M. haemolytica-positive calves (2 per load) were kept for additional daily cultures (POS; n = 4). Individual calf M. haemolytica status for both the POS and NEG groups was inconsistent between study days. Additionally, pulsed-field gel electrophoresis performed on isolates from the positive cultures showed that the NEG calves did not shed the M. haemolytica challenge strain, but rather 2 distinct clusters of M. haemolytica were shared among POS and NEG calves regardless of their initial status. Although sample sizes were small, these findings illustrate how variable the results of a single nasopharyngeal swab can be and the challenges of using an individual culture to truly represent animal M. haemolytica status.

The nasopharyngeal microbiota of feedlot cattle that develop bovine respiratory disease

Bovine respiratory disease is the major cause of morbidity and mortality in feedlot cattle. The objective of this study was to compare the nasopharyngeal bacterial microbiota of healthy cattle and cattle treated for BRD in a commercial feedlot setting using a high-density 16S rRNA gene microarray (Phylochip). Samples were taken from both groups of animals (n=5) at feedlot entry (day 0) and ≥60 days after placement. Cattle diagnosed with BRD had significantly less bacterial diversity and fewer OTUs in their nasopharynx at both sampling times. The predominant phyla in both groups were Proteobacteria and Firmicutes. The relative abundance of the phylum Actinobacteria was lower in cattle treated for BRD. At the family-level there was a greater relative abundance (P<0.05) of Micrococcaceae (day 0 only), Lachnospiraceae (≥60 days), Lactobacillaceae (day 0), and Bacillaceae (day 0) in healthy cattle compared to BRD-affected cattle. The community structure of the BRD-affected and healthy cattle were also significantly different from each other at both sampling times as measured using unweighted UniFrac distances. All entry samples of cattle diagnosed with BRD had 16S rRNA gene sequences representative of the BRD-associated bacteria Mannheimia haemolytica or Pasteurella multocida, although 3/5 healthy cattle were also positive for M. haemolytica at this time point. The results also indicate that the bovine nasopharyngeal microbiota is relatively unstable during the first 60 days in the feedlot.

Intestinal pathogens, diarrhoea and acute phase proteins in naturally infected dairy calves

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Multiple intestinal pathogen species were present in both healthy and diarrheic calves.

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Decreased haptoglobin concentrations were associated with weak signs of eimeriosis.

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Increased haptoglobin and fibrinogen concentrations were associated with respiratory tract infection and umbilical infection.

In this study, the association between Eimeria spp. related signs and innate immune response in dairy calves was examined. Calves (n = 100) aged 15–60 days were clinically examined and faecal samples, blood samples and deep nasopharyngeal swabs obtained. The samples were analysed for intestinal pathogens, acute phase proteins and WBC count, and respiratory tract pathogens, respectively.

Diarrhoea was diagnosed in 32.6% (23.3–43.0%, 95% CI) of calves. An association between the pathogenic Eimeria spp. and diarrhoea was detected by multiple correspondence analysis. Eimeria related signs (diarrhoea, presence of pathogenic species and total oocyst count) were combined resulting a four level variable. Calves with weak signs of eimeriosis had decreased haptoglobin concentrations (p = 0.02) and increased fibrinogen concentrations (p = 0.048) compared to no signs. Increased haptoglobin and fibrinogen concentrations were associated with respiratory tract infection and umbilical infection. Serum amyloid A and WBC counts showed no association with signs of eimeriosis or clinical diagnoses.

Nasal isolation of Mannheimia haemolytica and Pasteurella multocida as predictors of respiratory disease in shipped calves

Three hundred ninety five calves were purchased from sale barns and delivered to the Willard Sparks Beef Research Center. Nasal swabs were collected to determine if presence of Mannheimia haemolytica and Pasteurella multocida in the upper respiratory tract (URT) can facilitate diagnosis of bovine respiratory disease (BRD). Samples were collected at arrival and at treatment for BRD. Clinically healthy control calves were sampled at time of treatment of sick calves. M. haemolytica was more commonly isolated from calves at treatment than at time of arrival or from control calves. M. haemolytica was more common in calves requiring treatment than in those never treated. Need for treatment and number of treatments were negatively associated with average daily gain, supporting the accuracy of diagnosis. These results suggest that URT sampling, when combined with clinical diagnosis, may assist in providing greater diagnostic accuracy, improving ability to evaluate risk factors, interventions, and treatments.

Pathogens of bovine respiratory disease in North American feedlots conferring multidrug resistance via integrative conjugative elements

In this study, we determined the prevalence of bovine respiratory disease (BRD)-associated viral and bacterial pathogens in cattle and characterized the genetic profiles, antimicrobial susceptibilities, and nature of antimicrobial resistance determinants in collected bacteria. Nasopharyngeal swab and lung tissue samples from 68 BRD mortalities in Alberta, Canada (n = 42), Texas (n = 6), and Nebraska (n = 20) were screened using PCR for bovine viral diarrhea virus (BVDV), bovine respiratory syncytial virus, bovine herpesvirus 1, parainfluenza type 3 virus, Mycoplasma bovis, Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni. Excepting bovine herpesvirus 1, all agents were detected. M. haemolytica (91%) and BVDV (69%) were the most prevalent, with cooccurrence in 63% of the cattle. Isolates of M. haemolytica (n = 55), P. multocida (n = 8), and H. somni (n = 10) from lungs were also collected. Among M. haemolytica isolates, a clonal subpopulation (n = 8) was obtained from a Nebraskan feedlot. All three bacterial pathogens exhibited a high rate of antimicrobial resistance, with 45% exhibiting resistance to three or more antimicrobials. M. haemolytica (n = 18), P. multocida (n = 3), and H. somni (n = 3) from Texas and Nebraska possessed integrative conjugative elements (ICE) that conferred resistance for up to seven different antimicrobial classes. ICE were shown to be transferred via conjugation from P. multocida to Escherichia coli and from M. haemolytica and H. somni to P. multocida. ICE-mediated multidrug-resistant profiles of bacterial BRD pathogens could be a major detriment to many of the therapeutic antimicrobial strategies currently used to control BRD.

Serum IgG response in calves to the putative pneumonic virulence factor Gs60 of Mannheimia haemolytica A1

Bovine pneumonic pasteurellosis vaccines incorporate various antigens of Mannheimia haemolytica, including the acknowledged virulence factor leukotoxin (Lkt), and Gs60, a surface lipoprotein. To examine the role of antibodies to Gs60 in protection, an enzyme-linked immunosorbent assay (ELISA) was developed for retrospective analysis of serum samples from previous trials in which vaccines containing native or recombinant Gs60 were administered parenterally. The analysis revealed a positive correlation between the titer of antibodies to Gs60 and protection against experimental challenge in both vaccinates and naturally exposed controls. There was a strong correlation between production of IgG antibodies to Gs60 and Lkt neutralizing antibodies. Analysis of the relationship between the serum antibody titers and resistance to experimental challenge using linear statistical models revealed a significant association between prechallenge titers of serum antibodies to Lkt and protection. Further analysis suggested that antibodies against Gs60 were beneficial when Lkt neutralizing antibody titers were low.

Laboratory test descriptions for bovine respiratory disease diagnosis and their strengths and weaknesses: gold standards for diagnosis, do they exist?

The diagnosis of bovine respiratory diseases (BRD) poses significant challenges to the clinician as there are numerous infectious etiologies, operating singly or most often in combination. Clinical signs alone may not be diagnostic and the diagnostic laboratory is often used to assist the clinician. Recently many molecular-based tests have been taken from the research laboratory to the veterinary diagnostic laboratory. This review describes the "traditional tests" and several "molecular tests" and discusses the benefits and limitations of the tests and their interpretation. Clinicians should consult with their diagnostic laboratory regarding the interpretation of the test results. The rate of development and use of molecular diagnostic tests have outpaced validation, standardization, and standards for interpretation relative to their use in BRD diagnostics.

Prevalence of Pasteurella multocida and other respiratory pathogens in the nasal tract of Scottish calves

The prevalence of Pasteurella multocida, a cause of bovine respiratory disease, was studied in a random sample of beef suckler and dairy farms throughout Scotland, by means of a cross-sectional survey. A total of 637 calves from 68 farms from six geographical regions of Scotland were sampled between February and June 2008. Deep nasal swabs were taken, and samples that were culture-positive for P multocida were confirmed by PCR. Prevalence of P multocida was 17 per cent (105 of 616 calves); 47 per cent of farms had at least one positive animal. A higher prevalence was detected in dairy calves than beef calves (P=0.04). It was found that P multocida was associated with Mycoplasma-like organisms (P=0.06) and bovine parainfluenza type 3 virus (BPI-3) (P=0.04), detected by culture and quantitative PCR of nasal swabs, respectively. Detection of P multocida was not associated with bovine respiratory syncytial virus (BRSV), bovine herpesvirus type 1 (BoHV-1) or bovine viral diarrhoea virus (BVDV). Mycoplasma-like organisms, BPI-3, BRSV, BoHV-1 and BVDV were detected in 58, 17, four, 0 and eight calves, on 25, five, two, 0 and five of the 68 farms, respectively.

The epidemiology of bovine respiratory disease: what is the evidence for preventive measures?

Bovine respiratory disease (BRD) is the most common and costly disease of beef cattle in North America. Despite extensive research, industry practices are often more informed by dogma than by fact. Frequently advocated interventions, including vaccination, various processing procedures, and nutritional manipulation, have limited impact on morbidity and mortality. Evidence for use of oral antimicrobials, either in feed or water, appears to be equivocal. In contrast, preconditioning and metaphylaxis have significant scientific evidence of efficacy, with weaning prior to sale potentially being the most important component of preconditioning. The inability to reach more definitive conclusions in preventing BRD may be attributable to difficulties in investigating the disease. Study challenges include potential for extensive confounding, tremendous variability, the multi-factorial nature of the disease, and inadequate methods for diagnosis.

Metaphylactic antimicrobial therapy for bovine respiratory disease in stocker and feedlot cattle

This article provides an overview of implementing metaphylactic antimicrobial protocols to certain classes of cattle on arrival to stocker and feedlot production systems. The goal of this management practice is to reduce the negative health and performance effects induced by bovine respiratory disease (BRD). This article emphasizes the multiple factors that influence the decision for mass medication, including weight (age) of the cattle, distance traveled, environmental conditions, previous health history, visual inspection of the cattle at arrival, and prediction of the risk of disease. Current data suggest that metaphylactic programs significantly reduce negative health effects and improve feed performance that can be observed in cattle stricken with BRD.

Bacterial pathogens of the bovine respiratory disease complex

Pneumonia caused by the bacterial pathogens discussed in this article is the most significant cause of morbidity and mortality of the BRDC. Most of these infectious bacteria are not capable of inducing significant disease without the presence of other predisposing environmental factors, physiologic stressors, or concurrent infections. Mannheimia haemolytica is the most common and serious of these bacterial agents and is therefore also the most highly characterized. There are other important bacterial pathogens of BRD, such as Pasteurella multocida, Histophulus somni, and Mycoplasma bovis. Mixed infections with these organisms do occur. These pathogens have unique and common virulence factors but the resulting pneumonic lesions may be similar. Although the amount and quality of research associated with BRD has increased, vaccination and therapeutic practices are not fully successful. A greater understanding of the virulence mechanisms of the infecting bacteria and pathogenesis of pneumonia, as well as the characteristics of the organisms that allow tissue persistence, may lead to improved management, therapeutics, and vaccines.

Mollicutes species and Mycoplasma bovis prevalence and association with health outcomes in beef feeder calves at arrival and initial treatment for bovine respiratory disease

Mollicutes nasal swab culture status and potential associations with health outcomes were determined in beef feeder calves. Mollicutes culture was positive in 7.6% (22/291) of calves at arrival and in 26.2% (34/130) of calves at first disease treatment. Positive Mollicutes culture at first treatment was associated with increased odds for subsequent retreatment or death.

Bovine pasteurellosis and other bacterial infections of the respiratory tract

Despite technological, biologic, and pharmacologic advances the bacterial component of the bovine respiratory disease (BRD) complex continues to have a major adverse effect on the health and wellbeing of stocker and feeder cattle. Overlooked in this disappointing assessment is evaluation of the effects that working with younger, lighter-weight cattle have on managing the bacterial component of the BRD complex. Most problems associated with BRD come from cattle taken from and comingled with cattle operations that have inconsistent or nonexistent cattle health management. This article reviews the biologic, clinical, and management aspects of Pasteurella multocida, Mannheimia haemolytica, Histophilus somni, and Mycoplasma bovis, primarily as related to current production management considerations of stocker and feeder cattle.

Disease management of dairy calves and heifers

This article focuses on the most important diseases of dairy calves and heifers and presents clinical approaches that can improve detection, diagnosis, and treatment of herd-based problems. A systematic herd investigation strategy is pivotal to define the problems, understand important risk factors, develop a plan, and make recommendations for disease management accurately. A review of records, colostrum and feeding routines, housing and bedding management, routine procedures, vaccination, and treatment protocols begins the investigation and determines which diagnostic procedures and testing strategies are most useful. Disease management is most effective when the problem source is well defined and the exposure can be limited, calf immunity can be enhanced, or a combination of both. Screening examinations performed regularly or done at strategic time points improves detection of disease, can be used to monitor treatment outcomes, and can avoid disease outbreaks.

Pasteurella multocidaand bovine respiratory disease

Pasteurella multocidais a pathogenic Gram-negative bacterium that has been classified into three subspecies, five capsular serogroups and 16 serotypes.P. multocidaserogroup A isolates are bovine nasopharyngeal commensals, bovine pathogens and common isolates from bovine respiratory disease (BRD), both enzootic calf pneumonia of young dairy calves and shipping fever of weaned, stressed beef cattle.P. multocidaA:3 is the most common serotype isolated from BRD, and these isolates have limited heterogeneity based on outer membrane protein (OMP) profiles and ribotyping. Development ofP. multocida-induced pneumonia is associated with environmental and stress factors such as shipping, co-mingling, and overcrowding as well as concurrent or predisposing viral or bacterial infections. Lung lesions consist of an acute to subacute bronchopneumonia that may or may not have an associated pleuritis. Numerous virulence or potential virulence factors have been described for bovine respiratory isolates including adherence and colonization factors, iron-regulated and acquisition proteins, extracellular enzymes such as neuraminidase, lipopolysaccharide, polysaccharide capsule and a variety of OMPs. Immunity of cattle against respiratory pasteurellosis is poorly understood; however, high serum antibodies to OMPs appear to be important for enhancing resistance to the bacterium. Currently availableP. multocidavaccines for use in cattle are predominately traditional bacterins and a live streptomycin-dependent mutant. The field efficacy of these vaccines is not well documented in the literature.

Board-invited review: recent advances in management of highly stressed, newly received feedlot cattle

Morbidity and mortality from bovine respiratory disease (BRD) and associated losses in performance and carcass merit continue to plague the beef cattle industry. Several viral/bacterial agents are responsible for BRD, and interactions occur among the agents. Viral agents often predispose animals to bacterial infections, and Mannheimia haemolytica is the most frequently isolated organism in cattle with BRD. Laboratory tests are available to characterize organisms causing BRD using easily obtained nasal swab samples. Testing for persistent infection with bovine viral diarrhea virus can be done by a 2-stage technique using PCR and immunohistochemistry. Preconditioning programs that include preweaning viral vaccination programs along with castration could have a significant influence on decreasing BRD in the cattle feeding industry. Metaphylactic antibiotic programs continue to be effective; however, antibiotic resistance is a public concern, and additional management options (e.g., direct-fed microbials or other compounds with antimicrobial properties) deserve attention. Diets with an increased energy concentration achieved by decreasing the dietary roughage concentration may slightly increase the rate of BRD morbidity; however, these diets also increase ADG, DMI, and G:F compared with lower-energy, greater-roughage diets. The extent to which performance and BRD morbidity are affected by dietary protein concentration needs further study, but low and high protein concentrations should probably be avoided. Several trace minerals (e.g., Cu, Se, and Zn) affect immune function, but the effects of supplementation on performance and immune function in model challenge systems and in field studies are equivocal. Adding vitamin E to receiving diets at pharmacological levels (e.g., >1,000 IU x animal(-1) x day(-1)) seems beneficial for decreasing BRD morbidity, but it has little effect on performance. Given the limited ability to consistently modify immune function and BRD morbidity through dietary manipulations, we recommend that the diets for newly received cattle be formulated to adjust nutrient concentrations for low feed intake and to provide optimal performance during the receiving period.

Detection of tetracycline-resistant and susceptible pasteurellaceae in the nasopharynx of loose group-housed calves

The aim of the present study was to determine which Pasteurella and Mannheimia species are present in the upper respiratory tract of healthy calves with no history of antimicrobial treatment prior to sampling. The presence of subpopulations of tetracycline-resistant Pasteurellaceae was also investigated. Nasal swabs from 61 loose group-housed, clinically healthy calves, 1 to 4 months old, from 16 dairy herds were inoculated aerobically on a selective medium (Columbia agar with 5% ovine blood and 16 mg/L bacitracin) with or without 4 mg/L oxytetracycline (OTC). A total of 43 strains belonging to the family Pasteurellaceae were isolated from 38 calves (62.3%) out of 13 herds (81.3%). The predominant organisms were Pasteurella multocida subsp. multocida (57.4%), Mannheimia varigena (4.9%) and M. haemolytica (3.2%). Growth of Pasteurellaceae on the OTC-containing medium was seen only with samples from two herds (6 animals; 9.8%), and on only one farm this proved to be an OTC-resistant subpopulation. Minimum inhibitory concentration (MIC) determinations by means of agar dilution confirmed a low prevalence of OTC-resistant Pasteurellaceae, with overall MIC(50) and MIC(90) values of 0.25 and 32 mg/L, respectively. These data do not support the hypothesis that the relative high frequency of tetracycline-resistant P. multocida isolates from fatal cases of bovine respiratory disease is related to the presence of minor tetracycline-resistance subpopulations within this species.

Variability in acquired resistance of Pasteurella and Mannheimia isolates from the nasopharynx of calves, with particular reference to different herd types

To measure the level of antimicrobial resistance in potential bovine respiratory pathogens at different production types, nasal swabs were collected from 57 calves of 13 dairy herds, 150 calves of 9 beef cattle herds, and 289 calves of 5 high-density veal calf herds and investigated for the presence of Pasteurellaceae. All calves were less than 6 months old. Susceptibilities of the Pasteurella and Mannheimia isolates to eight antimicrobials were determined using an agar dilution method. P. multocida (37.3%) and hemolytic Mannheimia organisms (M. haemolytica sensu lato) (6.3%) were the most frequently detected organisms. The overall prevalence of isolates resistant to at least one antimicrobial from the dairy, beef, and veal calves were 17.6% (6/34), 21.9% (14/64), and 71.9% (64/89), respectively. In isolates obtained on the veal calf herds, acquired resistance to ampicillin, oxytetracycline, potentiated sulfonamides, gentamicin, tilmicosin, and enrofloxacin was frequently present, and 32.6% of these isolates were resistant to more than two of the tested antimicrobials. Resistance to ceftiofur and florfenicol was not detected. A substantial within-herd variability of species diversity and resistance profiles among isolates belonging to the genera Pasteurella and Mannheimia was found among the isolates of the veal calf farms.

Antimicrobial susceptibility of Mannheimia haemolytica isolates from cattle in Japan from 2001 to 2002

A total of 27 clinical isolates of Mannheimia haemolytica from cattle in Japan from 2001 to 2002 were examined for antimicrobial susceptibility to 25 antimicrobial agents. The minimum inhibitory concentrations of 25 different antimicrobials were determined by an agar dilution method according to the guidelines of the National Committee for Clinical Laboratory Standards. Of the 27 isolates, seven isolates (26.9%) were resistant to at least one of the 25 drugs and resistance rates ranged from 3.7 to 18.5%. Resistance rates to dihydrostreptomycin (18.5%), oxytetracycline (11.1%), and doxycycline (11.1%) were relatively high and those to the remaining drugs were less than 10%.

Efficacy of danofloxacin in the treatment of respiratory disease in European cattle

The efficacy of an injectable formulation of danofloxacin (180 mg/ml) in the treatment of naturally occurring bovine respiratory disease was evaluated in field studies on farms in France, Ireland and the United Kingdom. Cattle aged one week to 15 months with clinical respiratory disease were randomly allocated to treatment with 6 mg/kg danofloxacin or 10 mg/kg tilmicosin, administered by a single subcutaneous injection on day 0. A second injection of danofloxacin was administered on day 2, only if predefined clinical criteria were met. Mannheimia haemolytica, Pasteurella multocida and Haemophilus somnus were isolated from pretreatment nasopharyngeal swabs taken on all the farms. After the treatment, there was a more rapid improvement in the clinical response of the 178 animals treated with danofloxacin by day 2 (P < 0.01) than in the 90 treated with tilmicosin. For both treatments, there were similar significant (P < 0.001) reductions in the mean rectal temperature and severity of clinical signs of abnormal respiration and depression, on days 4 and 10 compared with day 0; 78.1 per cent of the animals treated with danofloxacin and 78.5 per cent of those treated with tilmicosin completed the studies. Danofloxacin 18 per cent was clinically safe and as effective as tilmicosin in the treatment of bovine respiratory disease.

Susceptibility testing for bovine respiratory and enteric disease

The interpretation of susceptibility results for antimicrobials with NCCLS-approved veterinary-specific breakpoints and where the methods also were NCCLS-approved are well established. When these same breakpoints are applied to other applications, however, the interpretation is not so clear. In these cases, a finding of S based on serial-dilution breakpoints puts the isolate in a defined population of bacteria with an MIC equal to or below the S breakpoint. An R result, in these cases, indicates that the organism may have an MIC equal to or greater (with no limits) than the R breakpoint. Extended-dilution testing yields more specific information about the isolate MIC. The relationship of disk-diffusion zone diameters to serial-dilution MICs is correlated on the basis of specific bacterial populations. When disk-diffusion results are interpreted for isolates other than those used for interpretive criteria development, the clinician is left wondering if the zone-diameter results now have a different relationship to serial-dilution results. Furthermore, the question of predictive value of the serial-dilution break-points still remains. The veterinary clinician should be aware of the differences in susceptibility testing predictive value for different applications. When approved veterinary-specific interpretive criteria are not available, then it is appropriate to keep records of clinical response related to susceptibility testing results for common therapies. Advice should be sought on the relationship of pathogen MICs to pharmacokinetic-pharmacodynamic parameters in these situations.

Effects of vaccination prior to transit and administration of florfenicol at time of arrival in a feedlot on the health of transported calves and detection of Mannheimia haemolytica in nasal secretions

OBJECTIVE

To determine effects of vaccination prior to transit and prophylactic administration of florfenicol at time of arrival at a feedyard on health of cattle and colonization of the nasopharynx by Mannheimia haemolytica (MH).

ANIMALS

121 steers from Tennessee and 84 steers from New Mexico.

PROCEDURE

Half of the steers were vaccinated before transport to a feedyard. Steers from Tennessee were vaccinated with MH bacterin-toxoid, and steers from New Mexico were vaccinated intranasally with modified-live leukotoxin-deficient MH. Half of the vaccinates and nonvaccinates were randomly selected to receive florfenicol on arrival at the feedyard. Steers were observed daily for respiratory tract disease (RTD).

RESULTS

Administration of florfenicol at time of arrival reduced the incidence of RTD, delayed the interval before onset of RTD, and reduced the incidence of MH colonization of the nasopharynx for at least 4 days, but vaccination did not have any effect. Vaccination elicited an increase in serum antibody titers to MH. Administration of florfenicol at time of arrival reduced the development of serum antibody titers in intranasally vaccinated steers and both groups of nonvaccinated steers, but intranasal vaccination did not affect colonization by wild-type MH.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of florfenicol at time of arrival decreased the incidence of MH organisms in the nasopharynx and delayed the onset of RTD. Prophylactic use of suitable antibiotics is likely to reduce the incidence of acute RTD in calves for several days after arrival at feedyards, which is the period when they are most susceptible to infectious organisms.

Coronavirus and Pasteurella infections in bovine shipping fever pneumonia and Evans' criteria for causation

Respiratory tract infections with viruses and Pasteurella spp. were determined sequentially among 26 cattle that died during two severe epizootics of shipping fever pneumonia. Nasal swab and serum samples were collected prior to onset of the epizootics, during disease progression, and after death, when necropsies were performed and lung samples were collected. Eighteen normal control cattle also were sampled at the beginning of the epizootics as well as at weekly intervals for 4 weeks. Respiratory bovine coronaviruses (RBCV) were isolated from nasal secretions of 21 and 25 cattle before and after transport. Two and 17 cattle nasally shed Pasteurella spp. before and after transport, respectively. RBCV were isolated at titers of 1 x 10(3) to 1.2 x 10(7) PFU per g of lung tissue from 18 cattle that died within 7 days of the epizootics, but not from the lungs of the remaining cattle that died on days 9 to 36. Twenty-five of the 26 lung samples were positive for Pasteurella spp., and their CFU ranged between 4.0 x 10(5) and 2.3 x 10(9) per g. Acute and subacute exudative, necrotizing lobar pneumonia characterized the lung lesions of these cattle with a majority of pneumonic lung lobes exhibiting fibronecrotic and exudative changes typical of pneumonic pasteurellosis, but other lung lobules had histological changes consisting of bronchiolitis and alveolitis typical of virus-induced changes. These cattle were immunologically naive to both infectious agents at the onset of the epizootics, but those that died after day 7 had rising antibody titers against RBCV and Pasteurella haemolytica. In contrast, the 18 clinically normal and RBCV isolation-negative cattle had high hemagglutinin inhibition antibody titers to RBCV from the beginning, while their antibody responses to P. haemolytica antigens were delayed. Evans' criteria for causation were applied to our findings because of the multifactorial nature of shipping fever pneumonia. This analysis identified RBCV as the primary inciting cause in these two epizootics. These viruses were previously not recognized as a causative agent in this complex respiratory tract disease of cattle.