Bovine respiratory disease is commonly diagnosed in cattle on the basis of clinical signs, with the decision to treat typically made on the basis of a high rectal temperature.1 Mycoplasma bovis is an important pathogen in BRD and one of the causes of calf pneumonia.2 Although a 2-staged approach is often used to establish whether a calf has BRD, studies3,4 have revealed that > 50% of pulmonary lesions detected at slaughter are in calves that were never treated for respiratory disease. The sensitivity and specificity of clinical signs of illness followed by confirmatory rectal temperature for diagnosing BRD are reportedly only 62% and 63%, respectively.5 These findings suggest that considerable opportunities exist to improve diagnostic accuracy for respiratory disease in cattle.
A CIS system is commonly used in the clinical assessment of animals and quantification or assignment of values that correspond to the probability of a specific outcome.6 By having multiple observers evaluate and assign a CIS to the same calf, the agreement among observers can be used to determine the repeatability of that CIS system. Determining the repeatability (a measure of precision) of a diagnostic test allows for a better understanding of the variability among observers, which can be used when evaluating methods to improve agreement and, thereby, allows consistent evaluation of disease status. The accuracy of a test refers to how well the test identifies the true status of an individual and is based on sensitivity and specificity.7 In BRD, the true disease status can be assessed on the basis of the amount of pulmonary damage at a given time point.
Given that CISs are used to make decisions regarding treatment effectiveness, an estimate of the system's performance as a diagnostic test is necessary to interpret results from any BRD study in which CISs are used to define inclusion criteria, to allocate experimental units, or to classify outcome (eg, case vs noncase). The objectives of the study reported here were to determine the precision of a CIS system as a diagnostic tool to identify clinical signs of illness in calves with experimentally induced M bovis pneumonia and to evaluate the accuracy of that system in relation to pulmonary consolidation scoring at necropsy.
Bovine respiratory disease
Clinical illness score
CEVA/Biomune, Lenexa, Kan.
Excede, Pfizer Animal Health, New York, NY.
Herd Maker Supreme B90, Land O' Lakes, Shoreview, Minn.
Calf Grower B-68 Medicated, Manhattan KS Coop, Manhattan, Kan.
Excel 2010, Microsoft Corp, Redmond, Wash.
Provided by CEVA/Biomune, Lenexa, Kan.
Koch Magnum 0.25 Stunner, KOCH Supplies Inc, Kansas City, Mo.
Stata/MP, version 12, StataCorp LP, College Station, Tex.
PROC GLIMMIX, SAS, version 9.2, SAS Institute Inc, Cary, NC.
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Trial characteristics in a 5-trial study to determine the usefulness of a CIS system for BRD diagnosis in Holstein bull calves inoculated with Mycoplasma bovis.
|Variable||Trial 1||Trial 2||Trial 3||Trial 4||Trial 5|
|No. of calves||24||42||16||43||53|
|No. of observers||7||8||7||5||5|
|Necropsy day*||14||13 and 14||24||12||13|
|Time of year||Sept–Dec||Jan–March||June–Aug||June–Aug||June–Sept|
Days are relative to the day on which M bovis pneumonia was experimentally induced (day 0).