• View in gallery

    Computer tomographic images obtained from a representative calf before (A) and 24 (B) and 72 (C) hours after inoculation with Mannheimia haemolytica. There is no lung consolidation before inoculation. Lung consolidation (arrows) is clearly evident 24 hours after inoculation but is smaller and less evident 72 hours after inoculation.

  • View in gallery

    Correlation between estimations for the percentage of lung consolidation by use of CT and affected lung surface area methods in 8 calves inoculated with M haemolytica (4 treated with florfenicol and 4 untreated control calves), with (A) and without (B) data for a statistical outlier. The correlation was R2 = 0.92 for data with the statistical outlier and R2 = 0.41 for data without the statistical outlier.

  • 1.

    Clinical and Laboratory Standards Institute. M31–A2. Performance standards for antimicrobial disk and dilution susceptibility tests for bacteria isolated from animals: approved standard. 2nd ed. Wayne, NJ: Clinical and Laboratory Standards Institute, 2002.

    • Search Google Scholar
    • Export Citation
  • 2.

    Fajt VR, Apley MD, Roth JA, et al. The effects of danofloxacin and tilmicosin on neutrophil function and lung consolidation in beef heifer calves with induced Pasteurella (Mannheimia) haemolytica pneumonia. J Vet Pharmacol Ther 2003;26:173179.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3.

    Fischbach F, Knollmann F, Griesshaber V, et al. Detection of pulmonary nodules by multislice computed tomography: improved detection rate with reduced slice thickness. Eur Radiol 2003;13:23782383.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4.

    Hayter AJ. A proof of the conjecture that the Tukey-Kramer multiple comparisons procedure is conservative. Ann Math Stat 1984;12:6175.

    • Search Google Scholar
    • Export Citation
  • 5.

    Gourlay RN, Thomas LH, Wyld SG. Experimental Pasteurella multocida pneumonia in calves. Res Vet Sci 1989;47:185189.

  • 6.

    Reeve-Johnson L. Relationships between clinical and pathological signs of disease in calves infected with Mannheimia (Pasteurella) haemolytica type A1. Vet Rec 2001;149:549552.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7.

    Vestweber JG, Klemm RD, Leipold HW, et al. Clinical and pathologic studies of experimentally induced Pasteurella haemolytica in calves. Am J Vet Res 1990;51:17921798.

    • Search Google Scholar
    • Export Citation
  • 8.

    Ames TR, Markham RJF, Opuda-Asibo J, et al. Pulmonary response to intratracheal challenge with Pasteurella haemolytica and Pasteurella multocida. Can J Comp Med 1985;49:395400.

    • Search Google Scholar
    • Export Citation
  • 9.

    Armbrust LJ, Mosier DA, Nelson EL, et al. Correlation of results of pulmonary computed tomography and pathologic findings in mice with Pasteurella-induced pneumonia. Am J Vet Res 2005;66:835838.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10.

    Cody DD, Nelson CL, Bradley WM, et al. Murine lung tumor measurement using respiratory-gated micro-computed tomography. Invest Radiol 2005;40:263269.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11.

    Elgeti T, Proquitte H, Rogalla NE, et al. Dynamic computed tomography in the neonatal lung: volume calculations and validation in an animal model. Invest Radiol 2005;40:761765.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12.

    Hyde RW, Wandtke JC, Fahey PJ, et al. Lung weight in vivo measured with computed tomography and rebreathing of soluble gases. J Appl Physiol 1989;67:166173.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13.

    Allan EM, Gibbs HA, Wiseman A, et al. Sequential lesions of experimental bovine pneumonic pasteurellosis. Vet Rec 1985;117:438442.

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Use of computed tomography to evaluate pathologic changes in the lungs of calves with experimentally induced respiratory tract disease

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  • 1 Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5701.
  • | 2 Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5701.
  • | 3 Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5701.
  • | 4 Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5701.
  • | 5 Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5701.
  • | 6 Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5701.
  • | 7 Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5701.

Abstract

Objective—To optimize methods for the use of computed tomography (CT) to assess pathologic changes in the lungs of calves and to determine the effect of treatment on lung consolidation.

Animals—10 male Holstein calves.

Procedures—Calves were anesthetized to facilitate CT imaging of the thorax. After initial images were obtained, pneumonia was induced in the calves by inoculation through a bronchoscope. Two calves were used in a preliminary study to refine the inoculation dose and optimize CT images. Four calves were administered florfenicol and 4 calves were untreated control animals. Serial images were obtained 24, 48, and 72 hours after inoculation. After final images were obtained, calves were euthanized, and lung consolidation was estimated by use of lung surface area scoring and water displacement. These estimates were compared with estimated lung consolidation obtained by use of CT.

Results—Calves had rapid disease progression. Percentage of lung consolidation was not significantly different between treatment groups for any of the estimation methods. Results of an ANOVA of the 3 assessment methods indicated significant differences among methods. Estimates of the percentage of lung consolidation obtained by use of surface area scoring and CT correlated well, whereas water displacement estimates correlated poorly with other methods of consolidation estimation.

Conclusions and Clinical Relevance—Because of the correlation with other methods for estimation of lung consolidation, CT has the potential to be used to monitor disease progression in calves with experimentally induced respiratory tract disease.

Abstract

Objective—To optimize methods for the use of computed tomography (CT) to assess pathologic changes in the lungs of calves and to determine the effect of treatment on lung consolidation.

Animals—10 male Holstein calves.

Procedures—Calves were anesthetized to facilitate CT imaging of the thorax. After initial images were obtained, pneumonia was induced in the calves by inoculation through a bronchoscope. Two calves were used in a preliminary study to refine the inoculation dose and optimize CT images. Four calves were administered florfenicol and 4 calves were untreated control animals. Serial images were obtained 24, 48, and 72 hours after inoculation. After final images were obtained, calves were euthanized, and lung consolidation was estimated by use of lung surface area scoring and water displacement. These estimates were compared with estimated lung consolidation obtained by use of CT.

Results—Calves had rapid disease progression. Percentage of lung consolidation was not significantly different between treatment groups for any of the estimation methods. Results of an ANOVA of the 3 assessment methods indicated significant differences among methods. Estimates of the percentage of lung consolidation obtained by use of surface area scoring and CT correlated well, whereas water displacement estimates correlated poorly with other methods of consolidation estimation.

Conclusions and Clinical Relevance—Because of the correlation with other methods for estimation of lung consolidation, CT has the potential to be used to monitor disease progression in calves with experimentally induced respiratory tract disease.

Research to evaluate therapeutic interventions for cattle with experimentally induced BRD has relied on the extent of pathologic changes in the lungs detected during postmortem examination as a primary measure of treatment effectiveness. These terminal measurements provide unique challenges to investigators. Ethical and economic concerns necessitate the use of a minimal number of animals for such studies; however, statistical power must be maintained. Terminal studies with multiple sample collection time points must typically use large numbers of animals to account for large variation among subjects.

Computed tomography can improve on postmortem examinations by allowing investigators to monitor disease progression in a single animal over time. This decreases the number of animals needed and also allows researchers to correlate actual pathologic changes of the lungs to clinical signs of disease. This technology is used extensively in human medicine to describe the extent and monitor the progression of pulmonary disease in cancer patients. Other veterinary researchers have investigated the use of CT in mice, pigs, and dogs with experimentally induced pulmonary disease. To our knowledge, CT has not been used to evaluate pathologic changes in the lungs of calves.

The objective of the study reported here was to develop and refine a method for the use of CT to assess pathologic changes in the lungs of calves with experimentally induced BRD. More specifically, the objectives were to evaluate the potential use of CT to measure the antemortem extent of pathologic changes in the lungs of calves with experimentally induced BRD and to use CT to determine the effect of antimicrobial treatment on those pathologic changes.

Materials and Methods

Animals—Ten male Holstein calves that were 6 to 10 weeks old and weighed between 44 and 79 kg were purchased from a university dairy teaching herd. Prior to purchase, calves were vaccinated by oral administration of a modified-live rotavirus and coronavirus vaccinea and intranasal administration of a modified-live infectious bovine rhinotracheitis virus and parainfluenza type 3 virus vaccine.b

Calves were housed separately in calf stalls in the university veterinary medical teaching hospital. A complete physical examination was performed on each calf at the time of arrival at the hospital. Calves were fed an antimicrobial-free milk replacerc and had ad libitum access to water for the duration of the study. The study was approved and monitored by the Kansas State University Institutional Animal Care and Use Committee (protocol No. 2482).

Study design—Prior to initiation of the study, a 14-gauge × 13-cm extended-use catheterd was inserted in the right jugular vein of each calf by means of standard procedures used at the veterinary teaching hospital. Two calves were used in a preliminary study to refine the experimental procedures. One calf died prior to completion of the preliminary study as a result of extensive lung damage caused by the inoculation. Therefore, a decreased inoculation dose and bronchoscopic delivery of the inoculum were used for the remainder of the calves to create pulmonary disease that was more focalized. Data obtained during the preliminary study were not included in subsequent statistical analyses.

The 8 remaining calves were used in a study conducted in 2 blocks (n = 4 calves/block); only 4 calves could be used each week because of the amount of time necessary to complete CT imaging procedures on each calf. Titers against Mannheimia haemolyticae were measured, and calves were blocked by titer within week. Within titer blocks, calves were assigned by use of a random number generator to receive antimicrobial treatment (n = 2) or to serve as untreated control calves (2). For block 1 (ie, week 1), titers against M haemolytica for the 2 treated calves were 1:512 and 1:2,048, respectively, whereas the titer for each of the 2 control calves was 1:1,024. For block 2 (ie, week 2), titers for the 2 treated calves were 1:128 and 1:256, respectively; titers for the 2 control calves were also 1:128 and 1:256, respectively.

Procedures—Each calf was anesthetized by administration of G-K-X solution, which consisted of guaifenesinf (50 mg/mL), ketamine hydrochlorideg (2 mg/mL), and xylazine hydrochlorideh (0.1 mg/mL). The G-K-X solution was administered IV to achieve the desired effect and enable oral intubation (mean ± SD volume infused, 60 ± 20 mL). An endotracheal tube (outside diameter, 12 mm) was inserted in each calf. Calves were then positioned in sternal recumbency on the CT table. Anesthesia was maintained with a continuous infusion of G-K-X solution to provide adequate relaxation for the duration of the imaging procedure.

CT imaging—Computed tomography was performed at approximately the same time each day on all 4 calves within a block. Daily CT imaging order was assigned by use of a Latin square design. Imaging procedures were repeated 24, 48, and 72 hours after the initial CT imaging and inoculation.

Immediately before CT imaging, a series of 5 to 7 positive-pressure breaths was delivered to each calf, with the final breath held at a pressure of 30 cm H2O for the duration of the 15- to 20-second scanning procedure. Imaging settings were 120 kVp and 170 mA. At the final inflation, each calf was moved through a helical scanner.i Scans were evaluated for evidence of insufficient lung inflation before anesthesia was discontinued. Images were archived and viewed on a PACSj for further evaluation. The number of breaths and holding pressure were determined in preliminary studies to be safe for the calves and were verified during the imaging procedure to be adequate for prevention of pulmonary atelectasis. Infusion of G-K-X was discontinued following the conclusion of the imaging procedures (except for the initial day of the study, when anesthesia was maintained until completion of the inoculation procedures). Total procedure time, including induction of anesthesia and CT imaging, rarely exceeded 10 minutes. Calves were extubated on return of the swallowing reflex and monitored for postanesthesia complications.

Inoculation—On the initial day of the study, calves were inoculated with a field isolate of M haemolytica. It was determined that the isolate was susceptible to florfenicolk (susceptible breakpoint of 2 μg/mL) with a minimum inhibitory concentration of ≤ 0.5 μg/mL. The minimum inhibitory concentration was determined by use of an extended-range microwell dilution system.l Testing was conducted in accordance with guidelines established by the CLSI, and determination of susceptibility was performed in accordance with CLSI-approved interpretive criteria.1

A serotype 1 isolate was grown overnight on brain-heart infusion platesm at 37°C in 5% carbon dioxide. Colonies from the plate were inoculated into brain-heart infusion brothn and incubated overnight on a rotary shaker° (180 revolutions/min) at 37°C. The suspension was then transferred to centrifuge tubes and centrifuged at 9,900 × g for 10 minutes at 4°C. Supernatant was decanted, and the pellet was double-washed with PBS solution at 9,900 × g for 10 minutes at 4°C. The pellet was resuspended to a final volume of 20 to 25 mL in PBS solution, which resulted in approximately 2.6 × 109 CFUs/mL (optical density = 1.155). Immediately after the initial CT imaging was completed, a 6.6-mm × 100-cm bronchoscopep was introduced through the endotracheal tube. The bronchoscope was guided into the accessory bronchus and lodged in a terminal bronchus, where half of the bacterial suspension (10 mL) was instilled through polyethylene tubing. The bronchoscope was then withdrawn into the trachea and advanced into one of the main bronchi of the right lung and lodged in a terminal bronchus, where the remaining bacterial inoculant (10 mL) was instilled.

Antimicrobial treatment—Twelve hours after inoculation, 4 calves (2 within each block [ie, week]) were administered florfenicolk (40 mg/kg, SC). Administration was in 1 site in the left cervical region by use of a 16-gauge, 0.75-inch needle.q

Evaluation of lung consolidation—After the final CT imaging 72 hours after inoculation, calves were euthanized by exsanguination under continued anesthesia. Thoracic organs were then removed, and gross description of pathologic changes in the lungs, scoring of affected lung surface area (as described elsewhere2), and water displacement measurements of total and affected lung were performed. Also, tissue samples were obtained for bacteriologic culture and histologic examination.

For water displacement measurements, the lungs were wrapped in clear plastic and immersed completely in a rigid container filled with water. The lungs were removed, and a graduated cylinder was used to refill the container. This volume was used for the total lung volume. For the affected lung volume, areas of affected lung were dissected, wrapped together in clear plastic, and immersed in a similar manner. Percentage of lung consolidation by water displacement was calculated by dividing the affected lung volume by total lung volume.

Bacteriologic culture—Samples were obtained from the junction between affected and normal lung tissues and submitted for bacteriologic culture. The surface of the tissue was seared, a cotton swab was inserted into the tissue, and the swab was streaked onto blood agar plates for bacterial growth and identification.

Histologic examination—Collected sections of normal and affected lung were fixed in neutral-buffered 10% formalin solution for 24 hours. Lung sections were trimmed to approximately 20 × 30 × 4 mm and placed into processing cassettes. After routine histologic processing, 4-μm-thick sections were cut from each block, mounted on glass slides, and stained with H&E. Histologic assessment by use of light microscopy was performed on each slide.

CT evaluations—Image slices for the initial CT images (before inoculation) were 10 mm, which resulted in a pitch of 1. Images for all 4 calves in the first block were analyzed at a slice interval of 10 mm, whereas images for the 4 calves in the second block were analyzed at a slice interval of 5 mm, which resulted in a pitch of 2 for that subset.3 Data for the 5-mm slices could be analyzed at 5- or 10-mm intervals.

All CT image slices were reviewed by a single reviewer, who was unaware of the treatment group and postmortem findings for the calves. Images were analyzed by use of a lung window in the PACS system. Total lung volume was calculated from the initial CT scan (no consolidation). The entire lung area of each slice was automatically selected by the area measurement tool as a region of interest. Mediastinal structures and pulmonary vessels were subtracted from the total measurement to yield the total area of lung per slice. This region-of-interest measurement was multiplied by slice interval to provide a volume measurement of total lung per slice. All measurements of volume per slice were summed to provide total lung volume per calf. For post-inoculation images, lung consolidation was subjectively estimated by the investigator; such estimation could include affected tissue and atelectic tissue near the area of pneumonia. Consolidation on serial scans was calculated by selecting areas of consolidated lung by use of the freehand tool on the PACS, then multiplying those areas by slice interval and calculating the sum for all slices. Therefore, this method averaged consolidated areas among slices. Percentage of consolidated lung was calculated for each time point by dividing the volume of consolidated lung by the volume of total lung determined for the initial CT scan.

Statistical analysis—Data for CT, water displacement values, and surface area measurements were entered into a spreadsheet programr for subsequent manipulation. Data were then transferred to a statistical software programs for evaluation of mean lung consolidation by treatment for each assessment method (CT, affected lung surface area, and water displacement) by use of an ANOVA. An ANOVA and pairwise comparisons of mean lung consolidation for each CT time point were also performed. Mean and SD for the percentage of lung consolidation were calculated for all ANOVA tests. Values were considered to differ significantly at P ≤ 0.05. When the ANOVA indicated significant differences, values were further analyzed by use of the Tukey-Kramer honestly significant difference method for multiple comparisons.4 Linear regression was performed to determine correlations among the 3 methods used to measure the percentage of consolidated lung. A statistical outlier necessitated that a second regression be performed for data for the CT and affected lung surface area.

Results

Gross pathologic changes—The first 4 calves had gross lesions characterized by extremely firm red-brown, gray, red, and black parenchyma. Multifocal areas of irregular regions consistent with necrosis were evident. Dense fibrin was located on the overlying pleura and within the interlobular septae. Extent and location of lung lesions differed slightly among calves.

The second group of 4 calves had lung lesions that were more focal in nature. Affected lung was characterized by firm, dark red to brown parenchyma. Interlobular septae were not prominent, and fibrin was not evident.

Bacteriologic cultureMannheimia haemolytica was isolated from lung tissues of both calves in the preliminary study. Mannheimia haemolytica was cultured from lung samples in 3 of 4 calves in the first block. However, none of the lung samples from the 4 calves in the second block yielded M haemolytica.

Histologic examination—Lung lesions for the 8 calves were histologically similar and varied only in the location and extent of lesions. Pulmonary architecture was distorted by large numbers of neutrophils and eosinophilic, fibrillar (fibrinous) fluid that filled the alveoli. In some areas of lung sections, alveolar macrophages were the prominent component of the cellular infiltrate. There were multifocal areas of parenchymal necrosis characterized by loss of architecture; multifocal aggregates of densely basophilic, spindle-shaped leukocytes; and abundant cellular debris intermixed with fibrillar eosinophilic fluid. Medium and small airways were consistently filled with variable numbers of neutrophils, cellular debris, and fibrin. Interlobular septae were moderately to extensively distended by loosely arranged fibrin and neutrophils. Interlobular lymphatics were often severely distended by fibrin thrombi, which often were intermixed with neutrophils.

Evaluation of lung consolidation—Mean lung consolidation did not differ significantly between treated and control calves for any of the 3 assessment methods (Table 1). Therefore, all calves were combined as 1 group for further statistical evaluation.

Table 1—

Mean ± SD percentage of lung consolidation as determined by use of 3 methods of assessment in 4 antimicrobialtreated calves and 4 untreated control calves after inoculation with Mannheimia haemolytica.

Table 1—

Percentage of lung consolidation at each CT time point differed significantly (P = 0.008). Use of the Tukey-Kramer honestly significant difference test revealed that mean lung consolidation before inoculation (0%) was significantly less than for all other time points. Numerically, 48 hours after inoculation had the highest mean lung consolidation, but mean ± SD values did not differ significantly among 24 (3.91 ± 2.68%), 48 (4.67 ± 3.69%), and 72 (3.79 ± 2.93%) hours after inoculation (Figure 1). Mean lung consolidation differed significantly between blocks (ie, weeks) for CT (P = 0.005) and water displacement (P = 0.017), with calves in the first block having more lung consolidation than calves in the second block. No difference was found between blocks for mean lung consolidation measured on the basis of affected surface area. Results of an ANOVA of the 3 assessment methods indicated significant (P = 0.037) differences among methods. Comparison of measured mean lung consolidation values by use of the Tukey-Kramer honestly significant difference test revealed that lung consolidation measured by CT was significantly lower than lung consolidation measured by the affected lung surface area and water displacement methods. There was no significant difference in measured lung consolidation between affected lung surface area and water displacement methods.

Figure 1—
Figure 1—

Computer tomographic images obtained from a representative calf before (A) and 24 (B) and 72 (C) hours after inoculation with Mannheimia haemolytica. There is no lung consolidation before inoculation. Lung consolidation (arrows) is clearly evident 24 hours after inoculation but is smaller and less evident 72 hours after inoculation.

Citation: American Journal of Veterinary Research 68, 11; 10.2460/ajvr.68.11.1259

Linear regression based on scatterplot comparisons revealed that mean lung consolidation measured by use of CT was highly correlated with mean lung consolidation measured by use of affected lung surface area (R2 = 0.92) when all calves were included (Figure 2). The prediction equation obtained from this regression was as follows: affected lung surface area = (2.058 × percentage of lung consolidation calculated for CT) + 0.028.

Figure 2—
Figure 2—

Correlation between estimations for the percentage of lung consolidation by use of CT and affected lung surface area methods in 8 calves inoculated with M haemolytica (4 treated with florfenicol and 4 untreated control calves), with (A) and without (B) data for a statistical outlier. The correlation was R2 = 0.92 for data with the statistical outlier and R2 = 0.41 for data without the statistical outlier.

Citation: American Journal of Veterinary Research 68, 11; 10.2460/ajvr.68.11.1259

Linear regression based on data that excluded the statistical outlier value yielded a weaker correlation (R2 = 0.41; Figure 2). The prediction equation for this regression was as follows: affected lung surface area = (1.2872 × percentage of consolidation calculated for CT) + 0.0487.

Linear regression between CT and water displacement resulted in a low correlation (R2 = 0.38). Linear regression between affected lung surface area and water displacement yielded a similarly low correlation (R2 = 0.21).

Discussion

In reviewing the published literature on pneumonic pasteurellosis in calves, we found many methods for experimental induction of BRD and evaluation of lung consolidation. In 4 studies,2,5–7 bacterial challenge ranged from 1.5 × 109 CFUs/animal to 7.9 × 1010 CFUs/animal (adjusted for differing inoculant volumes). In 2 of these studies,2,7 inoculations were delivered into a terminal bronchus, whereas endotracheal or transtracheal inoculations were used in the other studies.5,6 In only 1 study6 did investigators attempt to simulate natural disease by immunosuppressing the animals through transport. In all 4 of these studies, percentage of total lung consolidation was calculated by visually estimating the amount of affected lung during necropsy. Visual estimates were then converted to percentage of total lung consolidation by use of various mathematic methods. In the study reported here, we used one of those methods (affected lung surface area) to validate measurements obtained by use of CT.

With regards to inoculation dose, route of inoculation, and method for calculation of lung consolidation, the experimental design of the study reported here is similar to the experimental methods for the aforementioned studies.2,5–7 Mean lung consolidation in those other studies ranged from 13% to 50%. In comparison, the study reported here revealed mean lung consolidation values, as determined by 3 estimation methods, of approximately 10% when CT values were adjusted by use of estimates for affected lung surface area. Although 1 calf was considered a statistical outlier, the numeric values for percentage of consolidated lung in that calf (10.6% and 25.3% by use of CT and affected surface area, respectively) were not unreasonable for this type of study. The percentages of lung consolidation by use of the prediction equation obtained after excluding the statistical outlier were approximately 8.5%. Additional data are necessary for determining the precision of the prediction equation for a physiologically reasonable range of lung consolidation values.

When the inoculation dose and phase of bacterial growth were considered, the percentage of lung consolidation in the study reported here was consistent with the findings in another study8 in which investigators reported the mean ± SD percentage of lung consolidation in calves with experimentally induced BRD was 13.3 ± 7.6%. In another study,9 CT underestimated the percentage of consolidated lung in mice, compared with estimates obtained by use of microscopy. It is possible that positive-pressure ventilation would contribute to the underestimation of lung consolidation by CT because the lungs are comparatively deflated during postmortem examination. Additional research is needed to investigate these discrepancies between CT and postmortem estimates of lung consolidation.

The use of CT for estimating the amount of pathologic changes in the lungs has been studied in other animals. One such study10 validated the use of serial CT scans in mice with experimentally induced disease for detection and volumetric measurement of pulmonary nodules. Another study in mice9 revealed that CT estimates of lung consolidation were highly correlated with microscopic estimates of lung consolidation. Studies in which investigators used baby pigs11 and dogs12 revealed good agreement between total lung volume estimated by use of tracer gases and CT measurements. Those authors concluded that CT was reliable for in vivo assessment of total lung volume and estimation of the extent of pulmonary disease. Although helical CT was not used in those studies, the results reported here are encouraging for the use of helical CT in calves.

Results from the study reported here revealed no significant reduction in lung consolidation in the calves treated with florfenicol. With regard to treatment efficacy, few clinical conclusions can be drawn from this study because of the large variation within treatment groups, small percentage of total lung consolidation, and apparent rapid progression of lung lesions in relation to time of antimicrobial administration.

One of the unexpected findings in our study was the rapid progression of lung lesions after induction. In 1 report,13 which detailed the progression of gross and microscopic lesions after experimental induction of pneumonia in calves, investigators reported severe disease 2 or 3 days after inoculation (ie, the first necropsy time point). In another study,7 investigators used thoracic radiographs obtained 72 hours after induction to evaluate experimentally induced lung lesions, but correlations of radiographic lesions with gross and microscopic lesions were unreliable. We are not aware of any published studies in which lung lesions of cattle with experimentally induced pneumonia were evaluated < 48 hours after inoculation. Perhaps more extensive inoculation or immunosuppression of calves may lead to a more realistic method of infection and lesions that progress over a period > 24 hours.

To our knowledge, the study reported here is the first in which CT has been used to evaluate pathologic changes in the lungs of calves. Analysis of our results indicated that CT was correlated with antemortem lung consolidation in calves with experimentally induced BRD. Variability in the calculated percentage of lung consolidation from other studies and the study reported here suggests the need for additional research to refine the experimental methods. The utility of CT is potentially limited in studies such as this because of the cost of imaging, number of subjects that can be imaged, and need for anesthesia. However, CT provides a unique opportunity to evaluate progression of lung disease at serial time points in the same animal. The use of CT may provide researchers with the ability to minimize the number of animals, evaluate the experimental method used, and evaluate responses to treatment interventions before conducting large-scale field trials.

ABBREVIATIONS

BRD

Bovine respiratory disease

CT

Computed tomography

G-K-X

Guaifenesin-ketamine-xylazine

PACS

Picture archiving and communicating system

CLSI

Clinical and Laboratory Standards Institute

a.

Calf-Guard, Pfizer Animal Health, Exton, Pa.

b.

TSV-2, Pfizer Animal Health, Exton, Pa.

c.

Nursing Formula, Land O' Lakes Animal Milk Products, Shoreview, Minn.

d.

MILACATH, MILA International, Florence, Ky.

e.

Mannheimia haemolytica microagglutination, Texas Veterinary Medical Diagnostic Laboratory, Amarillo, Tex.

f.

Guaifenesin injection, Vedco Inc, St Joseph, Mo.

g.

VetaKet injectable, Lloyd Laboratories, Shenandoah, Iowa.

h.

Anased injectable, Lloyd Laboratories, Shenandoah, Iowa.

i.

Toshiba Express GX, Toshiba America Inc, New York, NY.

j.

Picture Archiving and Communicating System, Siemens Medical, Malvern, Pa.

k.

Nuflor, Schering-Plough Animal Health, Summit, NJ.

l.

Sensititer, Trek Diagnostic Systems Inc, Cleveland, Ohio.

m.

BBL BHI, Fisher Scientific, Pittsburg, Pa.

n.

BBL BHI + Bacto agar, Fisher Scientific, Pittsburg, Pa.

o.

Innova4000, New Brunswick Scientific, Edison, NJ.

p.

J556A flexible endoscope, Jorgensen Laboratories, Loveland, Colo.

q.

Monoject, Tyco Healthcare, Mansfield, Mass.

r.

Excel, Microsoft Corp, Redmond, Wash.

s.

JMP, version 5.1.2, SAS Institute Inc, Cary, NC.

References

  • 1.

    Clinical and Laboratory Standards Institute. M31–A2. Performance standards for antimicrobial disk and dilution susceptibility tests for bacteria isolated from animals: approved standard. 2nd ed. Wayne, NJ: Clinical and Laboratory Standards Institute, 2002.

    • Search Google Scholar
    • Export Citation
  • 2.

    Fajt VR, Apley MD, Roth JA, et al. The effects of danofloxacin and tilmicosin on neutrophil function and lung consolidation in beef heifer calves with induced Pasteurella (Mannheimia) haemolytica pneumonia. J Vet Pharmacol Ther 2003;26:173179.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3.

    Fischbach F, Knollmann F, Griesshaber V, et al. Detection of pulmonary nodules by multislice computed tomography: improved detection rate with reduced slice thickness. Eur Radiol 2003;13:23782383.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4.

    Hayter AJ. A proof of the conjecture that the Tukey-Kramer multiple comparisons procedure is conservative. Ann Math Stat 1984;12:6175.

    • Search Google Scholar
    • Export Citation
  • 5.

    Gourlay RN, Thomas LH, Wyld SG. Experimental Pasteurella multocida pneumonia in calves. Res Vet Sci 1989;47:185189.

  • 6.

    Reeve-Johnson L. Relationships between clinical and pathological signs of disease in calves infected with Mannheimia (Pasteurella) haemolytica type A1. Vet Rec 2001;149:549552.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7.

    Vestweber JG, Klemm RD, Leipold HW, et al. Clinical and pathologic studies of experimentally induced Pasteurella haemolytica in calves. Am J Vet Res 1990;51:17921798.

    • Search Google Scholar
    • Export Citation
  • 8.

    Ames TR, Markham RJF, Opuda-Asibo J, et al. Pulmonary response to intratracheal challenge with Pasteurella haemolytica and Pasteurella multocida. Can J Comp Med 1985;49:395400.

    • Search Google Scholar
    • Export Citation
  • 9.

    Armbrust LJ, Mosier DA, Nelson EL, et al. Correlation of results of pulmonary computed tomography and pathologic findings in mice with Pasteurella-induced pneumonia. Am J Vet Res 2005;66:835838.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10.

    Cody DD, Nelson CL, Bradley WM, et al. Murine lung tumor measurement using respiratory-gated micro-computed tomography. Invest Radiol 2005;40:263269.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11.

    Elgeti T, Proquitte H, Rogalla NE, et al. Dynamic computed tomography in the neonatal lung: volume calculations and validation in an animal model. Invest Radiol 2005;40:761765.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12.

    Hyde RW, Wandtke JC, Fahey PJ, et al. Lung weight in vivo measured with computed tomography and rebreathing of soluble gases. J Appl Physiol 1989;67:166173.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13.

    Allan EM, Gibbs HA, Wiseman A, et al. Sequential lesions of experimental bovine pneumonic pasteurellosis. Vet Rec 1985;117:438442.

Contributor Notes

Supported by Schering-Plough Animal Health.

The authors thank Donna Davis, Becky Pigsley, Donna Rogers, Sharon Tucker, and Kathy Shike for technical assistance.

Address correspondence to Dr. Lubbers.