Bovine Respiratory Disease Cases Research Articles

Feeding behavior as an early predictor of bovine respiratory disease in North American feedlot systems.

Bovine respiratory disease (BRD), which can cause substantial losses for feedlot operations, is often difficult to detect based solely on visual observations. The objectives of the current study were to determine a BRD case identification based on clinical and laboratory parameters and assess the value of feeding behavior for early detection of BRD. Auction-derived, mixed-breed beef steers (n = 213) with an average arrival weight of 294 kg were placed at a southern Alberta commercial feedlot equipped with an automated feed bunk monitoring system. Feeding behavior was recorded continuously (1-s intervals) for 5 wk after arrival and summarized into meals. Meals were defined as feeding events that were interrupted by less than 300 s nonfeeding. Meal intake (g) and meal time (min) were further summarized into daily mean, minimum, maximum, and sum and, together with frequency of meals per day, were fit into a discrete survival time analysis with a conditional log-log link. Feedlot staff visually evaluated (pen-checked) health status twice daily. Within 35 d after arrival, 76% (n = 165) of the steers had 1 or more clinical signs of BRD (reluctance to move, crusted nose, nasal or ocular discharge, drooped ears or head, and gaunt appearance). Whereas 41 blood samples could not be processed due to immediate freezing, for 124 of these steers, complete and differential blood cell count, total serum protein, plasma fibrinogen, serum concentration of haptoglobin (HP), and serum amyloid A (SAA) were determined. The disease definition for BRD was a rectal temperature ≥ 40.0°C, at least 2 clinical signs of BRD, and HP > 0.15 mg/mL. It was noteworthy that 94% of the 124 steers identified by the feedlot staff with clinical signs of BRD had HP > 0.15 mg/mL. An increase in mean meal intake, frequency, and mean inter-meal interval was associated with a decreased hazard for developing BRD 7 d before visual identification (P < 0.001). Furthermore, increased mean mealtime, frequency, and mean inter-meal interval were associated with a decreased BRD hazard up to 7 d before feedlot staff noticed clinical symptoms (P < 0.001). In conclusion, mean intake per meal as well as mean meal time and frequency of meals could be used to predict the hazard of BRD in feedlot cattle 7 d before visual detection and could be considered in commercial feedlot settings once a predictive algorithm has been developed.

Randomized clinical trial to evaluate the pathogenicity of Bibersteinia trehalosi in respiratory disease among calves.

BackgroundBibersteinia trehalosi causes respiratory disease in ruminants particularly in wild and domestic sheep. Recently, there has been an increased number of B. trehalosi isolates obtained from diagnostic samples from bovine respiratory disease cases. This study evaluated the role of B. trehalosi in bovine respiratory disease using an intra-tracheal inoculation model in calves. Thirty six cross bred 2–3 month old dairy calves were inoculated intra-tracheally with either leukotoxin negative B. trehalosi, leukotoxin positive B. trehalosi isolate, Mannheimia haemolytica, a combination of leukotoxin negative B. trehalosi and M. haemolytica or negative control. Calves were euthanized and necropsy performed on day 10 of study.ResultsB. trehalosi inoculated calves did not have increased lung involvement compared to control calves. Additionally, B. trehalosi was only cultured once from the lungs of inoculated calves at necropsy.ConclusionsBased on these findings B. trehalosi may not be a primary pathogen of respiratory disease in cattle. Culture of B. trehalosi from diagnostic submissions should not be immediately identified as a primary cause of respiratory disease.

Use of REP‐PCR and 16S rRNA gene sequencing for comparison of Mannheimia haemolytica isolates obtained from fatal cases of bovine respiratory disease in the USA and Australia

Assess the variability of Mannheimia haemolytica isolates obtained from fatal cases of bovine respiratory disease (BRD) in the USA and Australia using repetitive sequence-based PCR (REP-PCR) and sequencing of the 16S ribosomal RNA (rRNA) gene. We examined 22 isolates from the USA and 36 isolates from Australia using (GTG)5 and BOX-A1R REP-PCR primers, as well as sequencing a 700-base pair length of the 16S rRNA gene. The discriminatory ability of each typing method was assessed and correlation coefficients were calculated to assess concordance between the results of each approach. All methods appeared to discriminate among isolates, with BOX-A1R being the most sensitive and sequencing the least sensitive. Modest to moderate diversity was seen among the isolates, with as much variation within a continent as between the two. Using samples from diverse origins may permit extrapolation even to isolates with distant geographic and temporal relationships. Further, this information can serve as a baseline in assessing whether M. haemolytica is an opportunistic pathogen or if there are notable features that distinguish commensal isolates from those more likely to be associated with disease.

Systematic thoracic ultrasonography in acute bovine respiratory disease of feedlot steers

A study was conducted to evaluate the diagnostic and prognostic value of thoracic ultrasonography (TUS) in feedlot calves with clinical signs attributable to bovine respiratory disease (BRD). Twenty-nine BRD cases and 15 asymptomatic controls were evaluated using systematic TUS on the day of initial pull (day 0), and days 3, 6, 9, and 15. Four-second ultrasound loops were saved at 46 locations per animal and later evaluated off-line for evidence of lung pathology. Five TUS indicators of lung lesions and 4 indices of consolidation were evaluated for ability to differentiate between healthy controls and BRD cases, as well as predict death (negative outcome) among non-treated BRD cases. The number of sites with consolidation (SITES), number of sites with pleural irregularities (PIRR), maximal depth of consolidation (DEPTH), maximal area of consolidation (AREA), and total consolidated area (TCA) were found to be significantly higher in BRD cases than controls at enrollment (P less than 0.05). These same parameters (SITES, PIRR, DEPTH, AREA, TCA) were found to be significantly higher at enrollment for BRD cases that died before the end of the 15-day observation period (P less than 0.05). Among BRD cases, 9 of 46 sites examined had an odds ratio of negative outcome significantly greater than 1 when consolidation was present at enrollment (P less than 0.05). This study demonstrates that TUS may prove useful in feedlot cattle for determining the extent of lung lesions and predict outcome in BRD cases.

Survey of veterinarians in 6 US states regarding their experience with nursing beef calf respiratory disease

Bovine respiratory disease (BRD) is the leading cause of death of nursing beef calves 3 weeks of age and older, but little is known regarding risk factors for calf BRD. The objective of this survey was to describe observations and practices relevant to calf BRD by veterinarians in cow-calf practice. Recipients in Eastern (Georgia, Florida, and West Virginia) and Plains (Iowa, Kansas, and Nebraska) states were asked to complete an on-line questionnaire regarding events occurring between August 2011 and July 2012. A total of 574 veterinarians were solicited to participate; 61 (10.6%) returned responses suitable for inclusion, with an equivalent proportion responding from both regions. Respondents reported that 18% of their cow-calf clients recognized cases of nursing-calf BRD in the previous year, and 14% of their clients had at least 1 calf die of BRD. Infectious agents identified by antemortem or postmortem testing included Mannheimia haemolytica (60% of respondents); Pasteurella multocida (53%); Mycoplasma bovis (37%); bovine respiratory syncytial virus (33%); and bovine viral diarrhea virus (33%). Of responding veterinarians, 80% recommended or administered treatment for an outbreak of nursing-calf BRD in the previous year. Routine administration of respiratory vaccines to nursing beef calves was recommended by 87% of respondents. Respondents identified a variety of risk factors as potentially associated with calf BRD. Two of these, "introduction of cattle from outside sources" and "occurrence of diarrhea in calves", were also significantly associated with nursing-calf BRD in a previous survey of producers in the same states.

Antimicrobial multidrug resistance and coresistance patterns of Mannheimia haemolytica isolated from bovine respiratory disease cases—a three-year (2009–2011) retrospective analysis

Bovine respiratory disease continues to be the most important ailment of feed yard cattle. While the disease is multifactorial in nature, therapy continues to target the primary bacterial pathogens, Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni. A survey of records from a single diagnostic laboratory was conducted to evaluate the percentage of M. haemolytica isolates that were resistant to multiple antimicrobials and if coresistance patterns could be detected. All susceptibility test results for M. haemolytica recovered from lung tissues of cattle were eligible for inclusion in the survey. There were no isolates over the course of the analysis that were resistant to all 6 antimicrobials, primarily due to a lack of resistance to ceftiofur. In 2009, just over 5% of isolates were resistant to 5 or more antimicrobials (pan-resistant). In 2011, more than 35% of the M. haemolytica isolates were characterized as pan-resistant. Significant antimicrobial coresistance patterns were only seen with oxytetracycline and tilmicosin; bacterial isolates that were resistant to either oxytetracycline or tilmicosin were more likely to be resistant to at least one other antimicrobial. The mechanisms by which M. haemolytica is developing multidrug resistance warrant investigation if antimicrobial utility in the therapy of bovine respiratory disease is to be preserved.

Influence of tilmicosin on quantified pulmonary concentrations of three bacterial pathogens in calves with naturally-occurring bovine respiratory disease

A randomized trial was conducted to determine the lower respiratory tract pathogen load in cattle at risk of developing bovine respiratory disease (BRD). The objectives were to characterize and quantify concentrations of respiratory pathogens in the main-stem bronchi before and after administration of tilmicosin as a treatment for BRD.Ninety-three beef steers and heifers were selected from a group of 421 high-risk calves based on a BRD case definition that included clinical score and rectal temperature parameters. Three calves meeting the BRD case definition constituted a cohort; 1 animal within a cohort served as an untreated control, whereas the remaining 2 received 6.75 mg/lb (14.85 mg/kg) of body weight tilmicosin. An aliquot of solution obtained via lavage of the main-stem bronchi upon enrollment and at 72, 144, and 216 hours post-enrollment was serially diluted and cultured for respiratory bacteria.Treated animals had significant reductions (P&lt;0.05) in Mannheimia haemolytica concentrations at each post-enrollment time point compared to untreated controls, while concentrations of Histophilus somni at 144 and 216 hours post-enrollment were lower than untreated controls. Rectal temperature was also reduced (P&lt;0.05) at all post-enrollment sampling times in calves treated with tilmicosin. An improvement (P&lt;0.05) in clinical score during the post-enrollment period was noted for calves receiving tilmicosin.

Last Survey of Mycoplasma Bovis Prevalence in Polish Cattle Affected with Respiratory Syndrome

Abstract The aim of the study was to determine the prevalence of Mycoplasma bovis infection in clinical cases of bovine respiratory disease (BRD) in 2011. There were examined 841 serum samples and 41 nasal swabs and lungs of cattle from different farms of six regions of Poland (13 provinces). The obtained results indicated that the mean prevalence of M. bovis infection in Polish cattle population suffering from BRD was 64.3% and among them 8.4% of the animals were highly positive. On the other hand, in particular regions, it altered - 72.0% in east region, 52.7% in central region, 66.4% in south region, 64.1% in north-west region, 56.5% in north region, and 58.8% in south-west region. It should be added that within the presented regions, the highest values (82.4%) were reported in south region (Malopolskie province), whereas the lowest ones (42.9%) were in east region (Lubelskie province). However, field strains of M. bovis were isolated from the lungs of affected cattle only in the north-west region of Poland (Zachodniopomorskie province).

Integrated program for reducing bovine respiratory disease complex in beef and dairy cattle coordinated agricultural project (BRD CAP)

There is growing interest in selective breeding of livestock for enhanced disease resistance. Bovine respiratory disease (BRD), or pneumonia, is the largest single natural cause of death in US beef and dairy cattle, and BRD resistance represents an obvious target for selective breeding programs. The heritability of disease resistance is typically low, in part as a result of suboptimal diagnosis (i.e. not all sick animals are identified, healthy animals may be incorrectly diagnosed as ill, and some susceptible animals will appear resistant when in fact they have not been exposed). Additionally, the genetic basis of BRD susceptibility is likely complex and governed by the effects of multiple genes. This suggests a large number of case:control animals will be needed in datasets for disease susceptibility marker discovery. In 2011, the Agriculture and Food Research Initiative (AFRI) funded a five-year Coordinated Agricultural Project entitled "Integrated Program for BRD in Beef and Dairy Cattle". The overarching research objective of this multi-institutional "BRD CAP" project is to use newly-available genomic tools to identify host genome regions associated with susceptibility to BRD. During 2011, 2,000 dairy calves on a single large California facility were enrolled in a BRD case:control design study using an objective scoring system, and genotyped using a high-density bovine single nucleotide polymorphism (SNP) chip. It is envisaged that analyses of these data and future studies will lead to development of DNA tests to enable the selection of animals that are less susceptible to BRD, which is much-needed given growing concern regarding both animal welfare and use of antimicrobial therapeutics.

Effects of body weight loss during transit from sale barns to commercial feedlots on health and performance in feeder cattle cohorts arriving to feedlots from 2000 to 20081

Body weight loss during transport or shrink (SHK) is a common occurrence in feeder cattle that results from a physiological, complex process. Previous studies have assessed the effects of environmental and dietary stressors on transport-associated BW loss; however, data on associations between shrink and subsequent health and performance parameters in feeder cattle are limited. Operational data from 13 U.S. commercial feedlots (n = 16,590 cattle cohorts) were used to quantify how SHK was associated with bovine respiratory disease (BRD) morbidity and overall mortality risks, HCW and ADG in feeder cattle cohorts arriving to feedlots during 2000 to 2008. Multivariable mixed-effects negative binomial and linear regression models were employed to determine these associations while accounting for other cohort-level demographic variables. The median SHK among the study cohorts was 3.0% with a mean (± SEM) of 2.4 ± 0.02%. The mean (± SEM) cumulative BRD morbidity was 10.0% ± 0.09% (median = 5.8%; range 0 to 100%) and the mean (± SEM) overall cumulative mortality was 1.3% ± 0.01% (median = 0.9%; range: 0 to 25.6%). The mean and median number of days on feed of cohorts experiencing initial BRD cases was 143 and 150 d (range = 23 to 288 d). The effects of SHK were significantly (P < 0.05) associated with BRD morbidity, overall mortality, HCW and ADG, and these effects were significantly (P < 0.05) modified by gender, season and mean arrival BW of the cohort. Combining data on BW loss during transport with cohort demographics could allow a more precise prediction of health and performance of feedlot cattle.

Associations between weather conditions during the first 45 days after feedlot arrival and daily respiratory disease risks in autumn-placed feeder cattle in the United States1

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

Effects of group composition on the incidence of respiratory afflictions in group-housed calves after weaning

A study consisting of 2 experiments was conducted with the aim of determining the effects of previous history of bovine respiratory disease (BRD) on animal performance and health status of transition calves housed in groups. In both experiments, calves were housed in individual hutches until weaning age at 58 d. Before weaning, BRD incidences were individually recorded on a daily basis. Following weaning, calves were moved into super hutches in groups of 8, based on their history of respiratory afflictions, and growth performance and BRD incidences were recorded for 57 d. In experiment 1, 144 female Holstein dairy calves (initial BW = 72.6±1.2kg; age = 58.5±0.8 d) were distributed in 6 super hutches composed of 8 calves with no previous history of BRD (HHH), 6 super hutches composed of 6 calves without and 2 calves with a previous episode of BRD (HHR), and 6 super hutches housed 5 calves without a history of BRD and 3 calves with previous respiratory afflictions (HRR). In experiment 2, 144 Holstein female calves [58.0±0.9 d; 72.5±0.9kg of body weight (BW)] were distributed in 2 treatments consisting of 9 super hutches housing integrally 8 calves with no previous BRD, and 9 super hutches housing integrally calves with a previous BRD case. The number of BRD cases after weaning progressively increased from HHH to HRR as the proportion of calves previously affected by BRD within super hutch increased, mainly due to the fact that both animals affected by BRD before weaning and those with no previous history of BRD had more relapses in HHR and HRR groups than in the HHH group. Odds of incurring BRD after grouping were 3.89 greater in calves that had a previous case of BRD than in those that did not. The average time elapsed between commingling the animals and the appearance of the first BRD case was shorter when calves that had at least one BRD episode prior to weaning were present in a group (10.8±3.3 d) than when the group was formed with calves that had never experienced BRD before weaning (22.5±3.3 d). Final BW (at 115 d of life) and average daily gain tended to decrease as the number of BRD cases incurred increased. In experiment 2, calves in the HHH group reached a greater BW at the end of the study than those in the RRR group and tended to have a greater average daily gain in the HHH group than in the RRR group. It is concluded that forming groups of animals with a previous BRD history should minimize the incidence of respiratory cases in those groups of calves formed by animals without a previous history of respiratory disease.

Associations between several aspects of heifer development and dairy cow survivability to second lactation

A data set from 7,768 Holstein heifers born between 2004 and 2006, including growth rates from birth until first calving; age and body weight at insemination; and incidence of diarrhea, navel infections, and bovine respiratory disease (BRD) was used to evaluate potential associations between these factors and the odds of completing the first lactation. All heifers were raised in a contract heifer operation (Rancho Las Nieves, Mallen, Spain) and returned to their herds of origin (133 herds in total) before calving. Dates of death were provided by the Subdirección General de Explotaciones y Sistemas de Trazabilidad de los Recursos Agrícolas y Ganaderos from the Ministry of Environment, and Rural and Marine Areas of the Spanish government. At the time of analysis, 2,571 (33.1%) animals out of the 7,768 considered had died. In total, 655 (8.4%) heifers did not finish first lactation, and 31.5% of these left the herd within the first 50 DIM. Also, 4.8% of heifers aborted and were rebred. Data were analyzed using a mixed-effects logistic regression and survival analysis for dichotomous variables and a mixed-effects model for continuous ones. Incidence of diarrhea or navel infection was not associated with the chances of finishing the first lactation. Heifers that completed first lactation had a lesser average age at first calving (724±2 d) than those that did not (737±3 d). Heifers that reached second lactation grew (0.8±0.04 kg/d) more between 12 and 65 d of age than those that did not (0.7±0.04kg/d). As conception rate decreased, chances of leaving the herd before completing the first lactation increased. The number of AI services needed per conception as a nulliparous heifer was negatively associated with survivorship to second lactation. Heifers that experienced an abortion were 2.73±0.52 times more likely to leave the herd before completing the first lactation (but also calved with a much older age at first calving). Heifers that experienced 4 or more BRD cases before first calving had 1.87±0.14 greater odds of not completing the first lactation than those that never experienced BRD. These results show potential to forecast future heifer success in finishing the first lactation based on average daily gain early in life, incidence of BRD, reproductive performance (conception and abortion rates), and age at first calving.

Qualification and Quantification of Bacterial Pathogen Load in Acute Bovine Respiratory Disease Cases

In December 2009 a total 194 steers, bulls, and heifers weighing 400-700 lb (180-320 kg) were purchased at an Arkansas sale barn on a Friday and shipped 12 hours to a northern Kansas feedlot on Saturday. There was no previous history of treatment. The objectives of the study were to evaluate (1) bacterial pathogen isolates in different locations in the respiratory tract, (2) pathogen load in lung tissue as it corresponds to histology scores, and (3) total pathogen load in clinically ill and clinically normal calves.

Lung auscultation and rectal temperature as a predictor of lung lesions and bovine respiratory disease treatment outcome in feedyard cattle

Studies were conducted to examine the use of lung auscultation to predict bovine respiratory disease (BRD) case outcome in feeder cattle. In the first study, lung sounds were obtained and lung auscultation scores (LAS) were assigned by trained personnel. Antemortem physical examination and LAS were correlated with lung pathology and lung lesion scores at harvest. A field study was then conducted to determine LAS and case outcome in 4,341 feeder cattle treated for BRD. Lung auscultation score (P&lt;0.01) and rectal temperature (P&lt;0.01) were predictive of cattle with increased risk for BRD retreatment and mortality. The model-adjusted probability of a calf with a LAS of 2 requiring retreatment was 13%, whereas the probability of retreatment for cattle assigned a LAS of 9 was 63%. An increase in rectal temperature from 100.0 to 108.0°F (37.8 to 42.2°C) was correlated with a 266% increase in likelihood for retreatment for BRD. Risk of death from BRD increased nearly 2,200%, from 1.7% to 39%, as LAS increased from a score of 2 to 9. Risk of death due to BRD increased 196% as rectal temperature proceeded from 100.0 to 108.0øF. These studies demonstrate that lung auscultation score and rectal temperature could be useful to better predict BRD case outcomes in feeder cattle, and to facilitate targeted management decisions.

Comparison of Genotypic and Phenotypic Characterization Methods for Pasteurella Multocida Isolates from Fatal Cases of Bovine Respiratory Disease

Bovine respiratory disease (BRD) is the most costly disease of beef cattle in North America. Because Pasteurella multocida is a commensal of the upper respiratory tract, it is generally considered an opportunistic pathogen. However, studies in swine indicated that there may be a limited number of strains associated with disease, suggesting that some are more virulent than others. Although this may also be true of isolates from cattle, appropriate typing methods must be established before this possibility can be investigated. The purpose of this study was to compare effectiveness of polymerase chain reaction (PCR) fingerprinting to more traditional approaches for typing bovine P. multocida isolates. Isolates were obtained from 41 cases of fatal BRD and subjected to random amplified polymorphic DNA PCR (RAPD-PCR), whole cell protein (WCP) profiles, outer membrane protein (OMP) profiles, and serotyping. The discrimination index was calculated for each typing method and combinations of each using Simpson's index of diversity. Correlation coefficients were calculated to assess concordance between classification results achieved through genotypic (RAPD-PCR) and phenotypic (WCP, OMP, and serotyping) approaches. All characterization methods were capable of discriminating between isolates. However, there was poor concordance between techniques. There were also few significant associations between typing results and epidemiologic data. Random amplified polymorphic DNA PCR was validated as being a repeatable and reliable means of discriminating between P. multocida isolates obtained from cattle. Isolates obtained from fatal cases of BRD in calves in a commercial feedlot demonstrated significant diversity, justifying additional investigation into whether P. multocida is a strictly opportunistic pathogen in cattle.

Lung Pathology and Infectious Agents in Fatal Feedlot Pneumonias and Relationship with Mortality, Disease Onset, and Treatments

This study charted 237 fatal cases of bovine respiratory disease (BRD) observed from May 2002 to May 2003 in a single Oklahoma feed yard. Postmortem lung samples were used for agent identification and histopathology. Late in the study, 94 skin samples (ear notches) were tested for Bovine viral diarrhea virus (BVDV) by immunohistochemistry (IHC). Bovine respiratory disease morbidity was 14.7%, and the mortality rate of all causes was 1.3%, with more than half (53.8%) attributed to BRD (0.7% total of all causes). The agents isolated were the following: Mannheimia haemolytica (25.0%), Pasteurella multocida (24.5%), Histophilus somni (10.0%), Arcanobacterium pyogenes (35.0%), Salmonella spp. (0.5%), and Mycoplasma spp. (71.4%). Viruses recovered by cell culture were BVDV-1a noncytopathic (NCP; 2.7%), BVDV-1a cytopathic (CP) vaccine strain (1.8%), BVDV-1b NCP (2.7%), BVDV-2a NCP (3.2%), BVDV-2b CP (0.5%), and Bovine herpesvirus 1 (2.3%). Gel-based polymerase chain reaction (PCR) assays were 4.6% positive for Bovine respiratory syncytial virus and 10.8% positive for Bovine coronavirus. Bovine viral diarrhea virus IHC testing was positive in 5.3% of the animals. The mean values were determined for the treatment data: fatal disease onset (32.65 days), treatment interval (29.15 days), number of antibiotic treatments (2.65), number of different antibiotics (1.89), and day of death (61.81 days). Lesions included the following: 1) duration: acute (21%), subacute (15%), chronic (40.2%), healing (2.8%), normal (18.1%), and autolyzed (2.8%); 2) type of pneumonia: lobar bronchopneumonia (LBP; 27.1%), LBP with pleuritis (49.1%), interstitial pneumonia (5.1%), bronchointerstitial pneumonia (1.4%), septic (0.9%), embolic foci (0.5%), other (2.8%), normal (10.3%), and autolyzed (2.8%); and 3) bronchiolar lesions: bronchiolitis obliterans (39.7%), bronchiolar necrosis (26.6%), bronchiolitis obliterans/bronchiolar necrosis (1.4%), other bronchiolar lesions (6.5%), and bronchiolar lesion negative (25.7%). Statistically significant relationships were present among the agents, lesions, and the animal treatment, disease onset, and mortality data. Clinical illnesses observed in this study were lengthier than those reported 16-20 years ago, based on fatal disease onset, treatment interval, and day of death.

Molecular Characterization of Pasteurella multocida Isolates From Fatal Cases of Bovine Respiratory Disease

Bovine respiratory disease (BRD) is the most costly disease of beef cattle in North America. Mannheimia haemolytica is the most common cause of BRD, but recent work suggests that Pasteurella multocida is increasing in importance. Because P multocida is a commensal inhabitant of the upper respiratory tract, it is generally considered an opportunistic pathogen. However, studies in swine indicated that there may be a limited number of strains associated with disease, suggesting that some are more virulent than others. We hypothesize that similar strain differences exist in cattle. Polymerization chain reaction (PCR) fingerprinting is effective in discriminating between isolates of P multocida, but it has not been validated in bovine isolate.s. Therefore, the purpose of this study was to compare the effectiveness of PCR fingerprinting of P multocida isolates from cases of BRD to more traditional approaches, including whole cell protein (WCP) profiles, outer membrane protein (OMP) profiles and serotyping. The information obtained through these techniques was then used to examine isolate diversity to determine if disease was primarily attributable to a limited number of strains.

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.

Detection of Bovine Respiratory Syncytial Virus using a Heterologous Antigen-Capture Enzyme Immunoassay

Based on the marked antigenic similarities that exist between antigens of the human and bovine strains of respiratory syncytial virus (RSV), an enzyme immunoassay (EIA) designed to detect human RSV was used to detect bovine RSV. The commercial test kit (RSV EIA) consists of a solid phase (beads) coated with a capture antiserum prepared against the Long strain of human RSV. The RSV EIA test was compared with the method of inoculation of cell cultures and fluorescent antibody (FA) staining of lung tissue for the detection of bovine RSV. Using a cell culture-propagated stock of strain 375 of bovine RSV, the threshold of sensitivity of the EIA test for the cattle strain of RSV was determined to be less than or equal to 10(2.3) CCID50/ml. In addition, RSV EIA detected the bovine RSV in nasal samples obtained from 3 experimentally inoculated cattle. The RSV EIA exhibited a sensitivity of greater than or equal to 80% during the period that shedding of infectious virus took place. All of the bovine RSV FA-positive lung samples (n = 37) were positive by the RSV EIA. Twenty-six of the remaining 214 bovine RSV FA-negative lung samples were positive by the RSV EIA. The RSV EIA was also used to test 137 nasal swabs obtained from cases of bovine respiratory disease. Of these, 38 tested positive by RSV EIA. All samples that tested positive by EIA were confirmed by blocking assays using hyperimmune serum anti-bovine RSV and a pool of monoclonal antibodies specific for that virus.