Comparison of results for intradermal testing between clinically normal horses and horses affected with recurrent airway obstruction

OBJECTIVE: To evaluate differences in response to ID injection of histamine, phytohemagglutinin (PHA), and Aspergillus organisms between clinically normal horses and horses with recurrent airway obstruction (RAO). ANIMALS: 5 healthy adult horses and 5 adult horses with RAO. PROCEDURE: Intradermal testing (IDT) was performed on the neck with 2 positive control substances (histamine and PHA) and a mixture comprising 5 Aspergillus species. Four concentrations of each test substance plus a negative control substance were used. Equal volumes (0.1 mL) of each test substance were prepared to yield 15 syringes ([4 concentrations of each test substance plus 1 negative control substance] times 3 test substances) for each side of each horse (ie, 30 syringes/horse). Intradermal injections were administered; diameter of wheals was recorded 0.5, 4, and 24 hours after injection. RESULTS: Hypersensitive responses to ID injection of histamine were detected 0.5 hours after injection, and a delay in wheal formation after ID injection of Aspergillus mixture 24 hours after injection was detected in RAO-affected horses but was not observed in clinically normal horses. No differences were detected between the 2 groups after ID injection of PHA. CONCLUSIONS AND CLINICAL RELEVANCE: RAO-affected horses are hypersensitive to histamine, suggesting that RAO is associated with a heightened vascular response to histamine. Higher concentrations of Aspergillus mixture may be needed to detect horses that are sensitive to this group of antigens. Wheal reactions to Aspergillus may be a delayed response, suggesting that IDT results should be evaluated 0.5, 4, and 24 hours after ID injection.     

Determination of 'irritant' threshold concentrations for intradermal testing with allergenic insect extracts in normal horses

Abstract Sixteen healthy horses with no history of skin or respiratory disease were used for an intradermal testing (IDT) threshold study, in order to determine the concentrations of 13 commercial allergenic insect extracts most appropriate for IDT. Five dilutions of each extract were used, which included the manufacturer's recommended concentrations for equine IDT, plus one dilution higher and three lower than these standard concentrations. Allergens tested included caddisfly ( Trichoptera spp.), mayfly ( Ephemeroptera spp.), horsefly ( Tabanus spp.), deerfly ( Chrysops spp.), fire ant ( Solenopsis invicta ), black ant ( Camponotus pennsylvanicus ), cockroach mix ( Periplaneta americana and Blattella germanica ), mosquito ( Aedes aegypti ), house fly ( Musca domestica ), moth ( Heterocera spp.), flea ( Ctenocephalides canis / C. felis ), Culicoides variipennis and Culicoides nubeculosis. Two separate methods were used to calculate the allergen concentration for each insect extract where the normal horses, as a group, ceased to show false-positive ('irritant') reactions. 'Irritant' threshold concentrations were determined for 9/13 of these allergens, whereas the other 4 were undetermined due to either insufficient reactivity (flea, C. variipennis ) or excessive reactivity (black ant, moth) to the concentrations tested. Recommended concentrations for future use in equine patients with suspected insect hypersensitivity include: 125 pnu mL⁻¹ (mayfly); 250 pnu mL⁻¹ (caddisfly, horsefly, deerfly, fire ant, house fly); 500 pnu mL⁻¹ (cockroach); 1000 pnu mL⁻¹ (mosquito); and 1:10 000 w/v ( C. nubeculosis ).     

Evaluation of use of dimethyl sulfoxide for intra-articular lavage in clinically normal horses

The antebrachiocarpal and tarsocrural joints of 10 adult horses were randomly assigned to 1 of 4 groups. Groups were formulated and were treated as follows: group 1, control (arthrocentesis only); group 2, buffered lactated Ringer solution; group 3, 10% dimethyl sulfoxide (DMSO; w/v) in lactated Ringer solution; and group 4, 30% DMSO (w/v) in lactated Ringer solution. Joints were lavaged once with the respective solution. Prior to lavage and on days 1, 4, and 8 after lavage, all horses were evaluated for lameness and joint effusion; synovial fluid total and differential WBC counts, synovial fluid total protein concentration, and mucin clot quality were determined. Horses were euthanatized on day 8, and joints were evaluated grossly, histologically, and histochemically. Significant difference was not observed in effect of lactated Ringer solution, 10% DMSO, and 30% DMSO on any measured variable. At 24 hours after treatment, significant (P less than 0.05) difference in synovial fluid WBC numbers and total protein concentration was detected between control and treated joints. Eighty percent of lavaged joints had effusion 24 hours after treatment, compared with 30% of control joints. Gross, histopathologic, or histochemical differences were not detected between treated and control joints. Results of the study indicate that buffered lactated Ringer, 10% DMSO, and 30% DMSO solutions induce similar inflammatory changes in articular structures and significantly greater inflammatory reaction than does arthrocentesis alone.     

Evaluation of systemic immunologic hyperreactivity after intradermal testing in horses with chronic laminitis

OBJECTIVE: To determine whether systemic immunologic hyperreactivity exists in horses with chronic laminitis, compared with responses for nonlaminitic horses. ANIMALS: 7 nonlaminitic horses and 7 CL horses. PROCEDURE: In experiment 1, intradermal testing (IDT) was performed on 7 nonlaminitic and 7 CL horses to evaluate the response to a combination of 70 allergens at 15 and 30 minutes and 4 and 24 hours after injection. Three nonlaminitic and 3 CL horses used in experiment 1 were used in experiment 2 to determine whether histologic differences existed between the 2 groups. The H&E-stained tissue sections were evaluated on the basis of 3 criteria. For all analyses, 2-sample t-tests were used to determine significant differences between the groups. RESULTS: In experiment 1, CL horses had significantly higher total responses to IDT than nonlaminitic horses at the first 3 time periods. Also, CL horses had significantly fewer total scores of 0 than nonlaminitic horses at all time periods, except at 24 hours. In experiment 2, we did not detect significant differences between groups for any criterion. CONCLUSIONS AND CLINICAL RELEVANCE: Results support the hypothesis that CL horses develop hyperreactivity to various antigenic stimuli, compared with responses for nonlaminitic horses. Therefore, the possibility that antigenic challenge may result in exacerbation of clinical signs of laminitis should be discussed with horse owners. Chronic laminitis should also be a consideration when a horse becomes lame following antigenic challenges.     

Determination of threshold concentrations of multiple allergenic extracts for equine intradermal testing using normal horses in three seasons

Forty-one normal horses were evaluated for reactivity to intradermally injected aqueous allergens to determine allergen threshold concentrations (TC), with potential relevance to equine intradermal testing (IDT). Horses were tested three times over 1 year to assess seasonal variation in reactivity, using three to five serial dilutions of 27 allergens each time. Injection sites were evaluated after 15 min, 1 h, 4 h and 24 h. The highest allergen concentration at which < 10% of horses demonstrated positive reactivity (subjective score of > or = 2, scale of 0 to 4) at 15 min was considered the TC. The TC was determined for nine pollens (2000 to > 6000 PNU mL(-1)), four moulds (4000 to > 6000 PNU mL(-1)), seven insects (ant, horse fly 125 PNU mL(-1); house fly, cockroach 250 PNU mL(-1); moth 60 PNU mL(-1); mosquito 1000 PNU mL(-1); Culicoides nebeculosis 1 : 5000 w v(-1)) and three of four storage mites (1 : 10,000 w v(-1)). The TC was not determined due to excessive reactivity at the lowest concentrations tested for dust mites (Dermatophagoides farinae [< 1 : 12,000 w v(-1)], D. pteronyssinus [< 1 : 30,000 w v(-1)]), and Acarus siro (< 1 : 10,000 w v(-1)). Minor variation in the TC for specific allergens occurred in different seasons. Progressive sensitization with repeat testing occurred for grain mill dust mix. Positive reactivity at 1 h and 4 h occurred in > 10% of horses for nine of 19 allergens (pollens, mosquito, storage mites) at their determined TC. Positive reactivity was rare at 24 h. This study in normal horses suggests that appropriate testing concentrations of allergens for equine IDT in atopic horses may be > or = 1000 PNU mL(-1) for pollens and moulds, 60 to 250 PNU mL(-1) for most insects and < 1 : 12,000 w v(-1) for dust mites; and that reactions at 1-4 h may be insignificant.     

Suspected clinical Lyme disease in horses: Serological and antigen testing differences between clinically ill and clinically normal horses from an endemic region

Equine Lyme disease is difficult to diagnose because of its nonspecific clinical signs and the high incidence of subclinical infection in endemic regions. In this study we compared serology, antigen presence, hematology, blood chemistries and clinical presentation of 22 horses from a highly endemic region that were clinically diagnosed with Lyme disease to that of 21 clinically normal horses from the same region. We found that horses clinically diagnosed with Lyme disease were more likely to have Borrelia burgdorferi spirochetal DNA in their blood and urine, have a higher percentage of positive immunoblots containing antibodies to certain B. burgdorferi proteins, and tend to have higher ELISA titers than healthy horses from the same region. These results may help to improve diagnostic testing for equine Lyme disease.     

Effects of otic betamethasone on intradermal testing in normal dogs

Otitis externa is common in atopic dogs and is frequently treated using potent glucocorticoids topically. These preparations can cause adrenal suppression and affect skin test reactivity. The purpose of this study was to determine if an otic product containing betamethasone could decrease skin reactivity in normal dogs. Sixteen laboratory beagles were used in a cross-over, blinded trial. Dogs were enrolled in two groups; one received placebo and the other a betamethasone-containing otic preparation (Otomax) twice daily for 2 weeks. After a 4-week wash-out period, treatments were switched. Dogs were intradermally tested on days 0 and 14 of each treatment period with histamine phosphate (1 : 100,000 and 1 : 200,000 w/v) and allergens common in the area. Adrenocorticotropic hormone (ACTH) stimulation tests were done before and after treatment to investigate adrenal suppression. After 2 weeks of otic betamethasone, Dermatophagoides farinae (P = 0.0034), Cynodon dactylon (P = 0.0459) and histamine 1 : 100,000 w/v (P = 0.0028) reactions were significantly reduced. Pre-treatment post-ACTH serum cortisol levels and those obtained after both treatments did not differ statistically (P = 0.6362). Betamethasone induced a slight but statistically significant elevation (P = 0.0002) of serum alkaline phosphatase. Despite the increase, values were within normal range. It is concluded that, although otic betamethasone did not suppress adrenal glands, it mildly suppressed intradermal reactions to 1 : 100,000 w/v histamine, D. farinae and C. dactylon.     

Survey of resting blood pressure values in clinically normal horses

Resting coccygeal blood pressure values were measured, indirectly, on 296 horses (97 Thoroughbreds, 97 Standardbreds and 102 hacks). Blood pressure was found to vary with the class of horse examined; on average Thoroughbreds had significantly higher values than Standardbreds and hacks, whereas blood pressures of the last two groups were not significantly different. There was no demonstrable effect of sex, height or heart rate on blood pressure, but temperature and age did influence the value recorded. Mean (± sd) (n = 296) coccygeal uncorrected values (systolic pressure/diastolic pressure) were 112.1 ± 16.5/77.3 ± 14.3 mmHg. Allowing for bladder width to tail girth ratios used in each measurement, actual coccygeal pressures of 122.8 ± 18.6/71.0 ± 13.4 mmHg were determined. The latter corresponded to values of 149.4 ± 19.0/97.6 ± 14.0 mmHg, when corrected to heart (shoulder) level. Normal limits (defined as within 2.5th and 97.5th percentiles) for all horses, regardless of class, were 80 to 144 mmHg/49 to 105 mmHg for coccygeal uncorrected values and 86 to 159 mmHg/45 to 97 mmHg adjusted for bladder width to tail girth ratio.     

Comparative pharmacokinetics of meloxicam in clinically normal horses and donkeys

OBJECTIVE: To determine the disposition of a bolus of meloxicam (administered IV) in horses and donkeys (Equus asinus) and compare the relative pharmacokinetic variables between the species. ANIMALS: 5 clinically normal horses and 5 clinically normal donkeys. PROCEDURES: Blood samples were collected before and after IV administration of a bolus of meloxicam (0.6 mg/kg). Serum meloxicam concentrations were determined in triplicate via high-performance liquid chromatography. The serum concentration-time curve for each horse and donkey was analyzed separately to estimate standard noncompartmental pharmacokinetic variables. RESULTS: In horses and donkeys, mean +/- SD area under the curve was 18.8 +/- 7.31 microg/mL/h and 4.6 +/- 2.55 microg/mL/h, respectively; mean residence time (MRT) was 9.6 +/- 9.24 hours and 0.6 +/- 0.36 hours, respectively. Total body clearance (CL(T)) was 34.7 +/- 9.21 mL/kg/h in horses and 187.9 +/- 147.26 mL/kg/h in donkeys. Volume of distribution at steady state (VD(SS)) was 270 +/- 160.5 mL/kg in horses and 93.2 +/- 33.74 mL/kg in donkeys. All values, except VD(SS), were significantly different between donkeys and horses. CONCLUSIONS AND CLINICAL RELEVANCE: The small VD(SS) of meloxicam in horses and donkeys (attributed to high protein binding) was similar to values determined for other nonsteroidal anti-inflammatory drugs. Compared with other species, horses had a much shorter MRT and greater CL(T) for meloxicam, indicating a rapid elimination of the drug from plasma; the even shorter MRT and greater CL(T) of meloxicam in donkeys, compared with horses, may make the use of the drug in this species impractical.     

Evaluation of pituitary gland anatomy and histopathologic findings in clinically normal horses and horses and ponies with pituitary pars intermedia adenoma

OBJECTIVE: To determine size and weight of the pituitary gland and associations between pituitary gland size and weight and sex and age in horses without clinical signs associated with pituitary pars intermedia adenoma (PPIA) and horses and ponies with PPIA. ANIMALS: Pituitary glands from 100 horses without clinical signs of PPIA and 19 horses and 17 ponies with PPIA. PROCEDURES: Pituitary glands were weighed, measured, and examined histologically by use of H&E stain. Masson trichrome and periodic acid-Schiff staining were used, when appropriate. Histologic lesions in the pars intermedia, pars distalis, or both were classified as no significant lesions, single or multiple cysts, focal or multifocal hyperplasia, single or multiple microadenomas, and adenoma. Relative pituitary weight (RPW) was calculated as pituitary weight (grams) divided by body weight (grams). RESULTS: There was an age-related increase in the presence of pituitary lesions in the pars distalis and pars intermedia in geldings, mares overall, and non-pregnant mares. Mean (+/-SD) RPW in horses with PPIA was not significantly different from ponies with PPIA (15+/-5.9 x 10(-6) and 16+/-72 x 10(-6), respectively). Maximum pituitary weight in a horse with PPIA was 13.9 g (RPW, 2.9 X 10(-5)). Plasma glucose concentration was positively correlated with RPW in ponies with PPIA. CONCLUSIONS AND CLINICAL RELEVANCE: Pituitary lesions may be a factor in horses with insulin resistance and laminitis before development of clinical signs of PPIA. Ovarian steroids may be involved in the pathogenesis of lesions in the pars intermedia.     

Assessment of the ultrasonographic characteristics of the podotrochlear apparatus in clinically normal horses and horses with navicular syndrome

OBJECTIVE: To characterize the normal ultrasonographic appearance of the podotrochlear apparatus in horses by use of standardized measurements and identify soft tissue changes associated with navicular syndrome. DESIGN: Prospective study. ANIMALS: 7 clinically normal horses and 28 horses with navicular syndrome. PROCEDURE: The feasibility of identifying and measuring the soft tissue structures of the podotrochlear apparatus ultrasonographically via the transcuneal approach was assessed in 2 additional horses without navicular syndrome; both horses were euthanatized, and the structures identified ultrasonographically were confirmed at necropsy. Ultrasonographs were obtained in the study horses. Objective and subjective data were obtained to characterize ultrasonographic changes associated with navicular syndrome. RESULTS: Abnormalities of the flexor surface of the distal sesamoid (navicular) bone, the impar ligament, the distal digital annular ligament, deep digital flexor tendon (DDFT), and the podotrochlear (navicular) bursa were assessed via the transcuneal ultrasonographic approach. No significant differences were found between the measurements of the podotrochlear apparatus in normal horses and those with navicular syndrome; however, important subjective differences were detected ultrasonographically in horses with navicular syndrome. In horses with navicular syndrome, ultrasonographic findings were indicative of navicular bursitis, dystrophic mineralization of the DDFT and impar ligament, tendonitis and insertional tenopathy of the DDFT, desmitis of the impar ligament, and cortical changes in the flexor surface of the navicular bone. CONCLUSIONS AND CLINICAL RELEVANCE: Findings of ultrasonographic evaluation of the hoof appear to be useful in determining the cause of caudal heel pain and characterizing the components of navicular syndrome in horses.     

Evaluation of intravenous fluorescein in intradermal allergy testing in psittacines

This study was designed to improve the clinical feasibility of intradermal skin testing of psittacine birds using intravenous fluorescein stain. Twenty-five healthy, anaesthetized Hispaniolan Amazon parrots (Amazona ventralis) were injected intravenously with 10 mg kg-1 fluorescein-sodium 1% followed by intradermal injections of 0.02 mL phosphate-buffered saline, histamine phosphate (1:100,000 w/v) and codeine phosphate (1:100,000 w/v) at the sternal apteria. Wheal diameters of reaction sites were measured grossly and under illumination with a Wood's lamp after 5 and 10 min. Fluorescence-enhanced injection sites were scored between 0 and 2, with 0 equivalent to normal skin and 2 equivalent to a plucked feather follicle. The presence of a fluorescent halo around intradermal injections was also recorded. Under Wood's light illumination at 10 min, histamine and saline were evaluated as positive and negative controls, respectively, based on a positive test having a halo and a score of 2. Sensitivity and specificity were each 76% for halo, 84 and 42% for score and 64 and 77% for combination of score and halo, respectively. Further, mean histamine reactions were significantly larger than codeine phosphate and saline (8.8 +/- 0.4 mm; 7.2 +/- 0.3 mm; 5.9 +/- 0.6 mm); however, this finding was not consistent in individual birds. Wheal size, halo presence and score were affected by site location independent from the injected compound. Intravenous fluorescein improved the readability of avian skin tests; however, the compounds tested raised inconsistent reactions in wheal size, score or halo presence. The compound-independent site effect raises concern on the validity of avian skin testing and warrants investigation of other techniques such as in vitro allergy testing. Based on our findings, intradermal allergy testing in psittacines with or without fluorescein is unreliable and cannot be recommended for practical clinical use.     

Doppler ultrasonographic features of thoracic limb arteries in clinically normal horses

OBJECTIVES: To determine blood flow velocities and indices from spectral waveforms obtained by use of Doppler ultrasonography of thoracic limb arteries of horses and to assess interobserver and patient variability associated with the technique. ANIMALS: 9 clinically normal adult horses. PROCEDURE: Left thoracic limb arteries of 8 nonsedated horses were examined at 5 sites by use of pulsed-wave Doppler ultrasonography to determine a range of values for peak systolic, end diastolic, and mean velocities and resistive and pulsatility indices. Interobserver and patient variabilities were determined by 2 operators repeating similar measurements on 1 horse 8 times at weekly intervals. RESULTS: A range of values for each variable measured at the 5 selected sites was obtained. For each variable, strong positive correlations (R > or = 0.7) were detected for > 70% of the site-to-site comparisons made (excluding the coronary band). Among horses, resistive index varied least, whereas over time, mean velocity varied least. Waveform characteristics were consistent with resistive (n = 5) or nonresistive (4) patterns. In the single-horse experiment, waveform characteristics were consistent throughout the 8 weeks, and operator effects were not detected. CONCLUSIONS AND CLINICAL RELEVANCE: Doppler ultrasonography of no one site resulted in more reliable measurements of blood flow characteristics in thoracic limb arteries of horses. Mean velocity and resistive index were the least variable measurements made. Pulsed-wave Doppler ultrasonography may be a useful technique for evaluating diseases that alter normal thoracic limb arterial blood flow in horses.     

Detailed ultrasonographic mapping of the pelvis in clinically normal horses and ponies.

OBJECTIVE: To map the equine pelvis using ultrasonography, validated by use of computed tomography (CT), magnetic resonance imaging (MRI), and measurements of frozen cadaver slices. ANIMALS: 6 ponies and 6 horses. PROCEDURE: Ultrasonographic examination of the pelvis was performed on 6 clinically normal ponies. Measurements were obtained for imaged structures. Computed tomography, MRI, and measurements of frozen sections were performed after death and used to verify measurements. Linear regression determined the degree of correlation between measurements obtained ultrasonographically and the other modalities. Six clinically normal horses were then examined by use of ultrasonography. For each structure measured mean, SD, and range were calculated. RESULTS: Data obtained from ponies revealed high correlations between ultrasonographic findings and those of CT, MRI, and frozen section measurements (r2 = 0.97, r2 = 0.99, and r2 = 0.99, respectively). Differences between structures measured on each side of the pelvis were not significant. Variation in size of structures was not associated with weight of horses. A correlation was not found between weight of horses and ponies and size of structure. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasonography can be used to accurately measure and evaluate the musculoskeletal structures of the pelvis of horses. The use of CT, MRI, and measurements of frozen sections provided a means of validating the ultrasonographic measurements. Reference range values determined in our study can be used to evaluate horses with suspected pelvic disease.     

In vitro allergy tests compared to intradermal testing in horses with recurrent airway obstruction

Recurrent airway obstruction (RAO) is a common condition in stabled horses characterised by small airway inflammation, airway neutrophilia and obstruction following exposure of susceptible horses to mouldy hay and straw and is thus regarded as a hypersensitivity reaction to mould spores. However, the role of IgE-mediated reactions in RAO remains unclear.The aim of the study was to investigate with a serological IgE ELISA test (Allercept?), an in vitro sulfidoleukotriene (sLT) release assay (CAST^®) and with intradermal testing (IDT) whether serum IgE and IgE-mediated reactions against various mould, mite and pollen extracts are associated with RAO. IDT reactions were evaluated at different times in order to detect IgE-mediated immediate type reactions (type I hypersensitivity reactions, 0.5–1 h), immune complex-mediated late type reactions (type III reactions, 4–10 h) and cell-mediated delayed type reactions (type IV hypersensitivity reactions 24–48 h).In the serological test, overall the control horses displayed more positive reactions than the RAO-affected horses but the difference was not significant. Comparison of the measured IgE levels showed that the RAO-affected horses had slightly higher IgE levels against Aspergillus fumigatus than controls (35 and 16 AU, respectively, p < 0.05), but all values were below the cut off (150 AU) of the test. In the sLT release assay, seven positive reactions were observed in the RAO-affected horses and four in the controls but this difference was not significant.A significantly higher proportion of late type IDT reactions was observed in RAO-affected horses compared to controls (25 of 238 possible reactions versus 12 of 238 possible reactions, respectively, p < 0.05). Interestingly, four RAO-affected but none of the control horses reacted with the recombinant mould allergen A. fumigatus 8 (rAsp f 8, p < 0.05), but only late phase and delayed type reactions were observed.In all three tests the majority of the positive reactions was observed with the mite extracts (64%, 74% and 88% of all positive reactions, respectively) but none of the tests showed a significant difference between RAO-affected and control animals. Our findings do not support that IgE-mediated reactions are important in the pathogenesis of RAO. Further studies are needed to investigate whether sensitisation to mite allergens is of clinical relevance in the horse and to understand the role of immune reactions against rAsp f 8.     

Viscosity and rheologic properties of blood from clinically normal horses.

Blood viscosity (BV) was measured in 32 healthy horses at 6 spindle speeds (60, 30, 12, 6, 3, and 1.5 rpm) and for PCV of 40%, using a digital rotational cone and plate microviscometer. Also, in 7 of 32 horses, BV was measured 3 times each, for 3 PCV values (20, 40, and 60%), and at each spindle speed to determine effect of PCV on BV and machine and among-horse variations. Total plasma protein and fibrinogen concentrations were measured in all horses, using a standard refractometer and heat precipitation, respectively. In 7 of 32 horses, quantitative fibrinogen concentration was measured, using a quantitative fibrinogen assay. Plasma protein and fibrinogen concentrations were measured to determine their effect on BV. Plasma total protein (6.0 to 7.5 g/dl) and fibrinogen (100 to 400 mg/dl) concentrations were within normal reference range for our laboratory.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cytological and bacteriological findings in guttural pouch lavages of clinically normal horses

Percutaneous washes of the guttural pouches were obtained from two groups of 15 clinically normal horses, one lightly exercised and the other heavily exercised. Microbiological and cytological studies showed a wide variation in the differential cell counts. The cytological pattern of the normal lavages (< 5 per cent neutrophils) was characterised by a large proportion of ciliated columnar epithelial cells, a few non-ciliated cuboidal epithelial cells, and less than 1 per cent monocytes, lymphocytes, and eosinophils. Abnormal lavages (with more than 5 per cent neutrophils) had higher levels of bacterial growth than normal lavages. There were significant differences between the bacterial growth and total cell count, and also between the neutrophil contents of the lavages from the two groups of horses.     

Results of intradermal testing for the investigation of atopic dermatitis and recurrent urticaria in 50 horses in the south of England

Atopic dermatitis (AD) and recurrent urticaria (RU) are common immune‐mediated conditions of horses and ponies associated with high morbidity. Effective pharmacological treatment options are limited but identification of the causal allergens allows avoidance strategies and immunotherapy regimens to be employed. Intradermal testing (IDT) is the most widely accepted means of identifying the relevant allergens but there are no published reports of this technique being used in the UK for the investigation of dermatological disease. This study presents the results of testing with a varied panel of allergens in 50 horses with dermatological disease living in the south of England. Intradermal testing was performed in horses presented to The Liphook Equine Hospital for further investigation of AD or RU between June 2002 and March 2009. Allergen selection was based upon availability, results of previous studies, pollen charts and the likelihood of allergens being prevalent in the stable or pasture environment in the south of England. Injection sites were evaluated at 1 h (immediate phase), 4 h (late phase) and 24 h (delayed phase) and skin responses compared to the response generated by the positive control (histamine) at 1 h. Total numbers of positive reactions and numbers of positive reactions to specific allergens were similar in horses with atopic dermatitis and those with urticaria (P = 0.39). There was a statistically significant difference in the number of reactions observed at different time points, with more positive reactions occurring at 1 h than 24 h (P<0.001), and at 4 h than 24 h (P<0.001). Reading the test at 24 h rarely provides additional information. Reaction patterns were similar to those of previous studies performed in other countries with large numbers of positive reactions reported to mites, dusts and insects. Positive reactions were also common to allergens not previously identified as irritants or common allergens in equids; nettle, daisy, dandelion, horse chestnut, cat, cattle, sheep and pigeon. These allergens may be important causes of allergic dermatitis in equids in the UK; however, further studies should be performed in both normal horses and horses with allergic dermatitis to investigate irritant thresholds and validate these findings. Intradermal testing may be shortened from the conventional 24 h to 4 h without significantly affecting the results of the test.