Immune Cell Infiltration in Feline Meningioma.

Meningioma is the most common primary brain tumour in the cat. Although most of these tumours are considered to be benign based on histological characteristics, little is known regarding microenvironmental changes associated with the tumour. The characterization of the immune-cell infiltrate in human and canine meningiomas has been described; however, there are no data regarding the cat equivalent. Seventeen formalin-fixed, paraffin wax-embedded samples of feline meningioma were evaluated by light microscopy and immunohistochemistry (IHC) for expression of CD3, Pax5, Iba-1, HLA-DR, MAC387, CD163 and Ki67. Variable immune cell infiltrates were seen in every case. All tumours had moderate numbers of infiltrating CD3+ T lymphocytes. Seven of 17 tumours (41%) had infiltrating PAX5+ B lymphocytes that were often dispersed randomly throughout the neoplasm. Macrophage infiltration was abundant in all tumours with widespread immunoreactivity for Iba-1 and HLA-DR. Most tumours (15/17; 88%) had infiltration by MAC387+ macrophages; however, the number of infiltrating cells per ×400 field varied widely (from 0 to 57). Thirteen of 17 tumours (76%) had infiltration by CD163+ macrophages; however (similar to the MAC387 IHC), several tumours had numerous infiltrating cells. There was a potential weak negative rank correlation between the counts of CD3 and Ki67+ cells (rSp = -0.57; P = 0.018); however, no other rank correlations could be established between types of infiltrating immune cells (all other P ≥0.10). This study establishes evidence for a robust population of immune cells in feline meningioma and indicates that further study is needed to better understand the role of these cells with respect to tumour progression and post-surgical outcome.

Methods and Processes of Developing the Strengthening the Reporting of Observational Studies in Epidemiology - Veterinary (STROBE-Vet) Statement.

BACKGROUND: Reporting of observational studies in veterinary research presents challenges that often are not addressed in published reporting guidelines. OBJECTIVE: To develop an extension of the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement that addresses unique reporting requirements for observational studies in veterinary medicine related to health, production, welfare, and food safety. DESIGN: Consensus meeting of experts. SETTING: Mississauga, Canada. PARTICIPANTS: Seventeen experts from North America, Europe, and Australia. METHODS: Experts completed a pre-meeting survey about whether items in the STROBE statement should be modified or added to address unique issues related to observational studies in animal species with health, production, welfare, or food safety outcomes. During the meeting, each STROBE item was discussed to determine whether or not rewording was recommended and whether additions were warranted. Anonymous voting was used to determine consensus. RESULTS: Six items required no modifications or additions. Modifications or additions were made to the STROBE items 1 (title and abstract), 3 (objectives), 5 (setting), 6 (participants), 7 (variables), 8 (data sources/measurement), 9 (bias), 10 (study size), 12 (statistical methods), 13 (participants), 14 (descriptive data), 15 (outcome data), 16 (main results), 17 (other analyses), 19 (limitations), and 22 (funding). CONCLUSION: The methods and processes used were similar to those used for other extensions of the STROBE statement. The use of this STROBE statement extension should improve reporting of observational studies in veterinary research by recognizing unique features of observational studies involving food-producing and companion animals, products of animal origin, aquaculture, and wildlife.

Explanation and Elaboration Document for the STROBE-Vet Statement: Strengthening the Reporting of Observational Studies in Epidemiology-Veterinary Extension.

The STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement was first published in 2007 and again in 2014. The purpose of the original STROBE was to provide guidance for authors, reviewers, and editors to improve the comprehensiveness of reporting; however, STROBE has a unique focus on observational studies. Although much of the guidance provided by the original STROBE document is directly applicable, it was deemed useful to map those statements to veterinary concepts, provide veterinary examples, and highlight unique aspects of reporting in veterinary observational studies. Here, we present the examples and explanations for the checklist items included in the STROBE-Vet statement. Thus, this is a companion document to the STROBE-Vet statement methods and process document (JVIM_14575 "Methods and Processes of Developing the Strengthening the Reporting of Observational Studies in Epidemiology-Veterinary (STROBE-Vet) Statement" undergoing proofing), which describes the checklist and how it was developed.

Explanation and Elaboration Document for the STROBE-Vet Statement: Strengthening the Reporting of Observational Studies in Epidemiology - Veterinary Extension.

The STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement was first published in 2007 and again in 2014. The purpose of the original STROBE was to provide guidance for authors, reviewers and editors to improve the comprehensiveness of reporting; however, STROBE has a unique focus on observational studies. Although much of the guidance provided by the original STROBE document is directly applicable, it was deemed useful to map those statements to veterinary concepts, provide veterinary examples and highlight unique aspects of reporting in veterinary observational studies. Here, we present the examples and explanations for the checklist items included in the STROBE-Vet Statement. Thus, this is a companion document to the STROBE-Vet Statement Methods and process document, which describes the checklist and how it was developed.

Methods and Processes of Developing the Strengthening the Reporting of Observational Studies in Epidemiology - Veterinary (STROBE-Vet) Statement.

The reporting of observational studies in veterinary research presents many challenges that often are not adequately addressed in published reporting guidelines. A consensus meeting of experts was organized to develop an extension of the STROBE statement to address observational studies in veterinary medicine with respect to animal health, animal production, animal welfare and food safety outcomes. The consensus meeting was held 11-13 May 2014 in Mississauga, Ontario, Canada. Seventeen experts from North America, Europe and Australia attended the meeting. The experts were epidemiologists and biostatisticians, many of whom hold or have held editorial positions with relevant journals. Prior to the meeting, 19 experts completed a survey about whether they felt any of the 22 items of the STROBE statement should be modified and whether items should be added to address unique issues related to observational studies in animal species with health, production, welfare or food safety outcomes. At the meeting, the participants were provided with the survey responses and relevant literature concerning the reporting of veterinary observational studies. During the meeting, each STROBE item was discussed to determine whether or not re-wording was recommended, and whether additions were warranted. Anonymous voting was used to determine whether there was consensus for each item change or addition. The consensus was that six items needed no modifications or additions. Modifications or additions were made to the STROBE items numbered as follows: 1 (title and abstract), 3 (objectives), 5 (setting), 6 (participants), 7 (variables), 8 (data sources/measurement), 9 (bias), 10 (study size), 12 (statistical methods), 13 (participants), 14 (descriptive data), 15 (outcome data), 16 (main results), 17 (other analyses), 19 (limitations) and 22 (funding). Published literature was not always available to support modification to, or inclusion of, an item. The methods and processes used in the development of this statement were similar to those used for other extensions of the STROBE statement. The use of this extension to the STROBE statement should improve the reporting of observational studies in veterinary research related to animal health, production, welfare or food safety outcomes by recognizing the unique features of observational studies involving food-producing and companion animals, products of animal origin, aquaculture and wildlife.

Methods and processes of developing the strengthening the reporting of observational studies in epidemiology - veterinary (STROBE-Vet) statement.

BACKGROUND: The reporting of observational studies in veterinary research presents many challenges that often are not adequately addressed in published reporting guidelines. OBJECTIVE: To develop an extension of the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement that addresses unique reporting requirements for observational studies in veterinary medicine related to health, production, welfare, and food safety. DESIGN: A consensus meeting of experts was organized to develop an extension of the STROBE statement to address observational studies in veterinary medicine with respect to animal health, animal production, animal welfare, and food safety outcomes. SETTING: Consensus meeting May 11-13, 2014 in Mississauga, Ontario, Canada. PARTICIPANTS: Seventeen experts from North America, Europe, and Australia attended the meeting. The experts were epidemiologists and biostatisticians, many of whom hold or have held editorial positions with relevant journals. METHODS: Prior to the meeting, 19 experts completed a survey about whether they felt any of the 22 items of the STROBE statement should be modified and if items should be added to address unique issues related to observational studies in animal species with health, production, welfare, or food safety outcomes. At the meeting, the participants were provided with the survey responses and relevant literature concerning the reporting of veterinary observational studies. During the meeting, each STROBE item was discussed to determine whether or not re-wording was recommended, and whether additions were warranted. Anonymous voting was used to determine whether there was consensus for each item change or addition. RESULTS: The consensus was that six items needed no modifications or additions. Modifications or additions were made to the STROBE items numbered: 1 (title and abstract), 3 (objectives), 5 (setting), 6 (participants), 7 (variables), 8 (data sources/measurement), 9 (bias), 10 (study size), 12 (statistical methods), 13 (participants), 14 (descriptive data), 15 (outcome data), 16 (main results), 17 (other analyses), 19 (limitations), and 22 (funding). LIMITATION: Published literature was not always available to support modification to, or inclusion of, an item. CONCLUSION: The methods and processes used in the development of this statement were similar to those used for other extensions of the STROBE statement. The use of this extension to the STROBE statement should improve the reporting of observational studies in veterinary research related to animal health, production, welfare, or food safety outcomes by recognizing the unique features of observational studies involving food-producing and companion animals, products of animal origin, aquaculture, and wildlife.

Methods and Processes of Developing the Strengthening the Reporting of Observational Studies in Epidemiology-Veterinary (STROBE-Vet) Statement.

Reporting of observational studies in veterinary research presents challenges that often are not addressed in published reporting guidelines. Our objective was to develop an extension of the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement that addresses unique reporting requirements for observational studies in veterinary medicine related to health, production, welfare, and food safety. We conducted a consensus meeting with 17 experts in Mississauga, Canada. Experts completed a premeeting survey about whether items in the STROBE statement should be modified or added to address unique issues related to observational studies in animal species with health, production, welfare, or food safety outcomes. During the meeting, each STROBE item was discussed to determine whether or not rewording was recommended, and whether additions were warranted. Anonymous voting was used to determine consensus. Six items required no modifications or additions. Modifications or additions were made to the STROBE items 1 (title and abstract), 3 (objectives), 5 (setting), 6 (participants), 7 (variables), 8 (data sources and measurement), 9 (bias), 10 (study size), 12 (statistical methods), 13 (participants), 14 (descriptive data), 15 (outcome data), 16 (main results), 17 (other analyses), 19 (limitations), and 22 (funding). The methods and processes used were similar to those used for other extensions of the STROBE statement. The use of this STROBE statement extension should improve reporting of observational studies in veterinary research by recognizing unique features of observational studies involving food-producing and companion animals, products of animal origin, aquaculture, and wildlife.

Characterization of Inflammatory Changes Associated with Canine Oligodendroglioma.

Oligodendroglioma is a common glial tumour in the dog. In human neuropathology, the immune cell microenvironment of gliomas has been investigated; however, the nature of the inflammatory cells within canine gliomas is currently unknown. The aim of this study was to determine the nature of the immune cells and determine an association between the inflammatory cells and tumour grade. Thirty-four (18 of grade II and 16 of grade III) formalin-fixed and paraffin wax-embedded samples of canine oligodendroglioma were evaluated by light microscopy and immunohistochemistry for expression of CD3, PAX5, Iba-1, HLA-DR, Mac387 and CD31. Variations in immune cell recruitment and activation were evident in all cases. Infiltrating CD3(+) T lymphocytes were common in most cases. PAX5(+) B lymphocytes were less common and restricted to perivascular cuffs within or around the tumour. Iba-1(+) cells were common within the tumour and formed a dense infiltrate around the tumour in a subset of cases. HLA-DR(+) cells were common within the tumour and in a subset of cases formed perivascular cuffs. Iba-1(+) cells typically had prominent ramified processes suggestive of activated microglia, while the HLA-DR(+) cells had a more rounded morphology typical of amoeboid microglia. Rare Mac387(+) macrophages were found in the tumour parenchyma, while increased numbers of Mac387(+) monocytes were noted within the vasculature. No association or significance was established between the immune cell infiltrate and the grade of the tumour (all P ≥0.16). This study establishes that there is a robust population of immune cells within canine oligodendrogliomas and indicates that further study is needed to determine the role of these cells in tumour pathogenesis and progression.

Evaluation of maxillary arterial blood flow in anesthetized cats with the mouth closed and open.

The mouth-gag is a common tool used in veterinary medicine during oral and transoral procedures in cats but its use has recently been associated with the development of blindness. The goal of this study was to investigate whether maximal opening of the mouth affects maxillary artery blood flow in six anesthetized cats. To assess blood flow, the electroretinogram (ERG), brainstem auditory evoked response (BAER) and magnetic resonance angiography (MRA) were evaluated qualitatively with the mouth closed and open. During dynamic computer tomography (CT) examinations, detection of contrast medium in the maxillary artery was quantified by measuring the Hounsfield units (HUs). The peak HU, time to peak and mean HU were determined. Changes ⩾10% of these parameters were considered indicative of altered blood flow. ERG and BAER were normal with the mouth closed in all cats, but was abnormal with the mouth opened maximally in two cats and one cat, respectively. During MRA, blood flow was undetected in either maxillary artery in one cat and reduced in the right maxillary artery in two cats, when the mouth was open. During CT, the peak HU decreased ⩾10% in three cats, the time to peak was ⩾10% longer in two cats, and the mean HU was ⩾10% lower in one cat when the mouth was open. No cat developed apparent blindness or deafness. Maximal opening of the mouth caused alterations in several indicators of blood flow in some individual cats.

Dogs and horses with antibodies to outer-surface protein C as on-time sentinels for ticks infected with Borrelia burgdorferi in New York State in 2011.

Reported cases of Lyme disease (a chronic disease caused by infection with Borrelia burgdorferi) in humans increased more than two-fold between 1992 and 2006 in the United States. Recently, the annual number of reported human Lyme disease cases stabilized (according to the Center for Disease Control and Prevention) but the geographic distribution seemed to increase. In New York (NY) State, USA, a spread from the original Lyme disease focus in southeastern parts of the state has occurred. We determined incidence risks of new companion animal infection in 2011 with B. burgdorferi by county in 451 dog and 2100 horse sera; the samples were non-randomly collected by referring veterinarians in NY State between June 15, 2011 and January 31, 2012 because of suspicion of infection with B. burgdorferi or during annual health checks. All samples were submitted to the New York State Animal Health Center; the samples were submitted from 50 out of 62 counties in the state. Incident infections were determined by measuring antibodies to outer surface protein C (OspC; a marker of early infection that is detectable in serum from 3 weeks to 5 months after infection). Incident infections with B. burgdorferi were detected in 23% (95% confidence interval (CI): 19, 27) of canine samples and in 8% (95%CI: 7, 10) of equine samples. In 21 counties, samples were submitted from only one species (i.e. only dogs or only horses) that indicated incident infection. Recognition of incidence infections in dogs and horses might serve as a sentinel for infected ticks in different NY State counties; detection of the OspC antigen can provide a sensitive, new tool to allow recognition of risk for possible human and animal infection with B. burgdorferi by geographic region. We recommend that both dogs and horses be part of such a passive surveillance system.

Serum iron parameters and acute experimental EHV-1 infection in horses.

BACKGROUND: Research in humans has demonstrated that high serum iron (sFe) concentration can predispose to infection, and many infections subsequently result in alterations of host sFe. A decrease in sFe concentration is an early and sensitive indicator of systemic inflammation caused by tissue necrosis, bacterial infections, or endotoxemia in horses. Serum iron parameters in acute equine herpesvirus type 1 (EHV-1) infection have not been evaluated previously. OBJECTIVES: To document the sFe response to EHV-1 infection and to determine whether or not significant differences in sFe concentration exist between EHV-1 infected horses that develop neurologic disease and those that do not. ANIMALS: A total of 14 horses experimentally infected with EHV-1. METHODS: Data were collected as an ancillary data set during a blinded experimental EHV-1 infection. Horses were infected with the rAb4 strain of EHV-1. Temperature, neurologic score, packed cell volume (PCV), and sFe parameters (sFe concentration, % saturation, and total iron-binding capacity) were recorded daily for 2 weeks. Data were evaluated using Wilcoxon signed rank tests and Wilcoxon rank sum tests with Bonferroni corrections. CONCLUSIONS AND CLINICAL RELEVANCE: Serum iron concentration decreases significantly in a biphasic pattern after EHV-1 infection. There was no significant difference in sFe concentration in horses that developed neurologic disease and those that did not in these experimentally infected animals. Serum iron parameters may be useful in monitoring the clinical course of viral infections such as EHV-1.

The effect of premilking udder preparation on Holstein cows milked 3 times daily.

Premilking udder preparation (including forestripping and duration of lag time-the time between first tactile stimulation and attachment of milking unit) might influence milking measures such as milking unit on-time, incidence of bimodality, and milk flow rates in Holstein cows milked 3 times daily. Holstein cows (n=786) from an 1,800-cow commercial dairy herd were enrolled under a restricted randomized design to determine the effect of 9 different premilking routines. Lag times were 0, 60, 90, 120, and 240s and included forestripping or no forestripping for a total of 9 treatments (no forestripping for 0 lag time); the study was conducted from February to November 2008. All cow-treatment combinations were compared with the control: predipping plus forestripping and drying with 90s of lag time. Cows were initially assigned to 1 of 3 treatments for a period of 7d and upon completion of the first 7-d period were reassigned to a different treatment until all treatments had been completed. From one treatment period to the next, cows had to switch stimulation method with no restriction on lag time. Cows did not receive all treatments during the duration of the trial. Early- to mid-lactation cows (EML; 17-167 DIM) and late-lactation cows (LL; 174-428 DIM) were housed in 2 different pens. Milk yield was significantly different between dip + forestrip and dip+dry for 2 of the treatments for EML cows compared with dip + forestrip and 90 s of lag-time (DF90); however, this was not thought to be due to treatment because the significant lag times were very different (60 and 240 s) and neither was an extreme value. Milk yield did not differ with treatment for the LL cows. Milking unit on-time did not differ when comparing all treatments for EML with treatment DF90; however, an increase in milking unit on-time occurred when lag time was 60s or less for LL cows. The highest incidence of bimodal milk curves was when lag time = 0 and this was independent of stage of lactation; a lag time of 240 s had the second-highest incidence of bimodal milk curves for EML and LL cows. Milk harvested in the first 2 min was lower for lag times of 0 and 240 s when compared with DF90. Increasing the lag time for all cows appeared to improve overall milking time efficiency (although lag time had no effect on EML cows).

Equine stomachs harbor an abundant and diverse mucosal microbiota.

Little is known about the gastric mucosal microbiota in healthy horses, and its role in gastric disease has not been critically examined. The present study used a combination of 16S rRNA bacterial tag-encoded pyrosequencing (bTEFAP) and fluorescence in situ hybridization (FISH) to characterize the composition and spatial distribution of selected gastric mucosal microbiota of healthy horses. Biopsy specimens of the squamous, glandular, antral, and any ulcerated mucosa were obtained from 6 healthy horses by gastroscopy and from 3 horses immediately postmortem. Pyrosequencing was performed on biopsy specimens from 6 of the horses and yielded 53,920 reads in total, with 631 to 4,345 reads in each region per horse. The microbiome segregated into two distinct clusters comprised of horses that were stabled, fed hay, and sampled at postmortem (cluster 1) and horses that were pastured on grass, fed hay, and biopsied gastroscopically after a 12-h fast (cluster 2). The types of bacteria obtained from different anatomic regions clustered by horse rather than region. The dominant bacteria in cluster 1 were Firmicutes (>83% reads/sample), mainly Streptococcus spp., Lactobacillus spp. and, Sarcina spp. Cluster 2 was more diverse, with predominantly Proteobacteria, Bacteroidetes, and Firmicutes, consisting of Actinobacillus spp. Moraxella spp., Prevotella spp., and Porphyromonas spp. Helicobacter sp. sequences were not identified in any of 53,920 reads. FISH (n = 9) revealed bacteria throughout the stomach in close apposition to the mucosa, with significantly more Streptococcus spp. present in the glandular region of the stomach. The equine stomach harbors an abundant and diverse mucosal microbiota that varies by individual.

Three-dimensional conformal versus non-graphic radiation treatment planning for apocrine gland adenocarcinoma of the anal sac in 18 dogs (2002-2007).

Differences in dose homogeneity and irradiated volumes of target and surrounding normal tissues between 3D conformal radiation treatment planning and simulated non-graphic manual treatment planning were evaluated in 18 dogs with apocrine gland adenocarcinoma of the anal sac. Overall, 3D conformal treatment planning resulted in more homogenous dose distribution to target tissues with lower hot spots and dose ranges. Dose homogeneity and guarantee of not under-dosing target tissues with 3D conformal planning came at the cost, however, of delivering greater mean doses of radiation and of irradiating greater volumes of surrounding normal tissue structures.

Comparison of two questionnaires to assess gastrointestinal toxicity in dogs and cats treated with chemotherapy*.

Questionnaires completed by pet owners are widely used instruments to monitor adverse gastrointestinal (GI) effects in the owners' animals undergoing chemotherapy and for reporting toxicoses in clinical trials; however, no questionnaires have been formally evaluated. This study compares two questionnaire-based evaluations of adverse GI events: a basic, open-ended questionnaire and a detailed questionnaire modelled after the grading in the Veterinary Co-operative Oncology Group-Common Terminology Criteria for Adverse Events (VCOG-CTCAE). Owners completed both questionnaires after their dog or cat received moderately emetogenic chemotherapy. Results were used to derive toxicity grades for anorexia, vomiting and diarrhoea. We evaluated 123 pairs of questionnaires. Disagreement in grade of anorexia, vomiting and diarrhoea was found in 24, 7 and 13% of paired questionnaires, respectively (κ = 0.63, 0.83 and 0.71, respectively). Although 'good' to 'very good' agreement was found, the potential for only 'fair' agreement between questionnaire methods is of concern and suggests a need to adopt a standardized form.

A fluorescent bead-based multiplex assay for the simultaneous detection of antibodies to B. burgdorferi outer surface proteins in canine serum.

Lyme disease is a zoonotic, vector-borne disease affecting humans, dogs, horses and other species. It is caused by infection with spirochetes of the Borrelia burgdorferi sensu lato group which are transmitted to the mammalian host by infected ticks (Ixodes). Exposure to B. burgdorferi is commonly diagnosed by serological testing. The gold standard for the detection of antibodies to B. burgdorferi is a two-step procedure of an ELISA followed by confirmatory Western blotting (WB). Here, we developed and validated a new bead-based multiplex assay for the detection of antibodies to B. burgdorferi in canine serum which combined the testing by ELISA and WB in a single quantitative test. B. burgdorferi outer surface protein A (OspA), OspC and OspF were expressed in E. coli. The recombinant proteins were coupled to fluorescent beads providing the matrix of the assay. Two sets of canine sera were used for validation of the multiplex assay. First, sera from 79 dogs with known ELISA and WB results were used to establish the conditions of the assay. These samples were selected to provide similar numbers of pre-tested sera ranging from negative to high positive results and included sera from vaccinated and/or naturally infected dogs. A high correlation was observed for detection of antibodies to B. burgdorferi in the single and multiplex assays (n=79). Spearman's rank correlations were 0.93, 0.88 and 0.96 for OspA, OspC and OspF, respectively. Second, a total of 188 canine serum samples that were not tested previously were used for further multiplex assay validation. All samples were also blindly analyzed for antibodies to B. burgdorferi antigens by WB. The WB results provided a 'relative gold standard' for each antigen and were used to perform a receiver operating curve analysis. The areas under the curves were 0.93 for OspA, 0.82 for OspC, and 0.89 for OspF. Multiplex assay interpretation ranges for antibodies to all three B. burgdorferi antigens in canine serum were established by likelihood analysis. The diagnostic sensitivities of the individual OspA, OspC and OspF bead-based assays were 83%, 62% and 82%, respectively, and the diagnostic specificities were 90%, 89% and 86%, respectively. The new multiplex assay provides a sensitive and fully quantitative platform for the simultaneous evaluation of antibodies to B. burgdorferi OspA, OspC and OspF antigens and distinguishes between antibodies that originated from vaccination or natural exposure to B. burgdorferi.

An immunohistochemical study of vitamin D receptor expression in canine cutaneous mast cell tumours.

The active form of vitamin D (1alpha, 25-dihydroxycholecalciferol; calcitriol) has potent anti-neoplastic activity in the management of a number of human malignancies. Despite promising data to suggest that calcitriol is an effective adjunct to current chemotherapy modalities, the role of calcitriol in animal neoplasia is poorly understood. Vitamin D inhibits growth of canine mast cell tumours (MCTs) in vitro, presumably due to ligand-mediated activation of the vitamin D receptor (VDR). The aim of the present study was to examine immunohistochemically the expression of the VDR by reactive and neoplastic canine cutaneous mast cells. Expression was graded according to frequency, intensity and score (frequency x intensity). VDR expression was found in all samples containing reactive mast cells (n=9), and in 67 of 69 (97%) MCTs selected from each of the three Patnaik grades. The frequency and score of VDR labelling was greater in MCTs compared with reactive mast cells (P=0.0005 and 0.001, respectively). There was no difference in VDR frequency between the MCT grades, but the frequency of labelling in grade 3 MCTs was higher than for reactive mast cells (P=0.001). There was no association between tumour mitotic index and any of the three VDR variables (all P>0.16). VDR is widely expressed by reactive and neoplastic canine mast cells in vivo. VDR expression is unlikely to represent an independent prognostic factor, but its presence within biopsy specimens might be used to identify patients that are suited to high-dose vitamin D therapeutic trials.