Treatment Of Pastern Dermatitis Biology Essay

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This trial assessed the efficacy of an ointment containing kunzea oil for the treatment of horses with localised acute or chronic pastern dermatitis. Horses (n=37) were randomly allocated to treatment with an ointment containing either 20% kunzea oil (test) or 2% ketoconazole (control). Due to a high dropout rate, 21 horses completed the study. The severity of the lesions was assessed before and after seven days of treatment. The kunzea oil formulation resulted in a significant (P<0.01) decrease in total lesion area from a total lesion area of median value 40 cm2 (range 3-252 cm2) to 0 cm2 (range 0-34 cm2), with complete resolution of pastern dermatitis signs in 7 of 11 cases after seven days. The control formulation resulted in no significant change in total lesion area, with complete resolution of pastern dermatitis signs in two of 10 cases after seven days. The kunzea oil ointment was significantly more effective than the control formulation, based on both lesion area reduction and clinical scoring improvement (P<0.01). Horses treated with kunzea oil ointment beyond the seven day period demonstrated improvement in their condition that was not formally assessed. Both ointments were well tolerated with no adverse reactions reported. The kunzea oil ointment was safe, fast-acting and effective in treating pastern dermatitis in the study cohort and may offer a suitable treatment option for pastern dermatitis in the general horse population.

Introduction

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Pastern dermatitis, also known as grease heel or greasy heel, scratches, mauke or mud fever, is a progressive dermatitis. Usually, it begins with erythematous lesions in the plantar pastern region, more often of the hind legs. Lesions typically develop scaling that progresses to the release of a malodorous exudate and crust formation, with associated alopecia (Stannard, 1972, Hungerford, 1975). Oedema is common and may extend to the fetlock and lower cannon area. Lesions may spread to the dorsal pastern and cannon regions. Due to constant flexion skin fissures may develop from which, in severe cases, bleeding is common (Blood et al., 1981). With chronicity, more often in heavy breeds, nodular skin masses or verrucous skin lesions may develop. Acute lameness can result from severe cases when treatment is neglected or is unsuccessful (Stannard, 1972, Hungerford, 1975, Blood et al., 1981, Geburek et al., 2005).

Pastern dermatitis is a syndrome that may involve various inflammatory skin conditions that arise from a number of different pathophysiological processes. These include mite infestation, bacterial infection, dermatophytosis, dermatophilosis, photosensitisation, vasculitis, vaccinia, pemphigus foliaceus and primary irritant contact dermatitis (Scott and Miller, 2003, Risberg et al., 2005). One study has implicated a coagulase-positive Staphylococcus intermedius in a case of vasculitis (Risberg et al., 2005), however, the pathogenesis of the disease state was uncertain. It was suggested that vasculitis may be responsible for most cases of idiopathic pastern dermatitis (Stannard, 2000, Knottenbelt, 2002).

Although pastern dermatitis affects all breeds it is most common in heavy draught horses, and in particular those with feathering. In heavy breeds there has not been found to be an association with pastern colour (Geburek et al., 2005); however in other breeds, the condition more commonly affects non-pigmented pasterns, suggesting a greater role for photosensitization in the development of pastern dermatitis in these horses.

Due to similar clinical signs upon presentation, it can be impossible to differentiate the underlying cause of the pastern dermatitis. A differential diagnosis requires pathological investigations, including one or more of skin punch biopsy with histological examination, hairmat culture and microscopy (Risberg et al., 2005). Anecdotal reports, however, suggest that the condition is generally treated without prior determination of a specific diagnosis, except in severe cases.

To the authors' knowledge, there are no clinical studies that have thoroughly evaluated treatment options for pastern dermatitis. Anecdotal reports suggest that treatment is often initiated by horse owners and that various home remedies are used, including preparations containing substances such as copper sulphate, kerosene and sulphur. Not surprisingly, the condition often persists for months or even years (Scott and Miller, 2003). Treatment by veterinarians is commonly empirical and is determined by the stage of the disease. Treatment and preventative recommendations include separation of the horse from potential agents of the disease by its removal from wet, muddy and otherwise unhygienic conditions, as well as avoidance of potential chemical, plant-derived or environmental irritants (Scott and Miller, 2003).

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General treatment recommendations include the clipping of hair in the affected area and simple cleansing, the removal of crust, and the application of antimicrobial agents, an astringent or a hypertonic and drawing preparation. In more advanced cases a topical antibiotic or corticosteroid ointment may be recommended. Systemic corticosteroid therapy in horses with vasculitis has been recommended (Stannard, 2000); however, it has also been suggested that systemic antibiotics, not corticosteroids, should be the first treatment choice for such cases (Risberg et al., 2005). The use of both systemic antibiotics and systemic corticosteroids has been suggested, when indicated (Scott and Miller, 2003). A set of recommendations for the treatment of different forms of pastern dermatitis has been proposed (Risberg et al., 2005). These include: removal of hair, crusts around the lesional areas and cleaning of the infected areas with antiseptic (chlorhexidine or povidone-iodine) solution. Use of fungicidal wash (anilconazole, natamycin or benuldasic acid) together with the application of 10% povidone solution or teritiary amine disinfectant scrub is suggested in cases where dermatophytic infection is diagnoised.

There appears to be a need for a simple, clinically-proven treatment option for non-severe cases of pastern dermatitis. A formulation has been developed by a Tasmanian pharmacist from a region containing numerous racing stables. This formulation, called Greasy HealTM, has been used for many years, with anecdotal reports indicating a high success rate in the treatment of pastern dermatitis (Armstrong, 2004). A key ingredient of the formulation is the essential oil obtained from the shrub Kunzea ambigua. Experiments (agar dilution assay) in our laboratory have shown that the oil is active (MIC values ranging from 0.3-1.0% v/v) against a range of bacterial (including S. aureus, S. epidermis, Dermatophilus congolensis) and fungal organisms (dermatophyte spp., yeast spp.), which are involved in the pathogenesis various cutaneous infections in humans and animals (unpublished results). Kunzea oil has been listed as a medicine by the Therapeutic Goods Administration in Australia for topical application (AUSTL 72143, 1996). The purpose of this current study was to evaluate the efficacy of an ointment formulation containing kunzea oil in the treatment of pastern dermatitis, within a randomised controlled design.

Materials and methods

Study subjects

Horses of either gender, with localised pastern dermatitis and without any other obvious signs of disease or injury, were eligible for the study. Exclusion criteria included pastern dermatitis caused by mites; pastern dermatitis with severe swelling; the use of topical or systemic corticosteroids, antifungals, antibiotics or herbal medicines within 2 weeks of (or during) the study; and pregnancy or lactation.

Initially, owners of horses with pastern dermatitis were approached by their treating veterinarians and invited to participate in the study. Subsequently, word-of-mouth publicity resulted in approaches directly from horse owners requesting participation in the study. Before entering the trial a signed consent form was obtained from each horse's carer or owner. A diagnosis of pastern dermatitis was made on the basis of compatible history and clinical signs. This diagnosis was reliant on each veterinarian's clinical judgement based on many years of equine veterinary experience. Thirty seven horses with pastern dermatitis were enrolled in to the study through six veterinarians from Tasmania (5) and South Australia (1).

Study medications

Kunzea oil was obtained from J. J. Hood, Waterhouse, Tasmania. Ketoconazole was obtained from Sharon Pharmaceuticals (Mumbai, India). Each formulation contained pharmaceutical grade zinc oxide (5 % w/w), salicylic acid (5 % w/w), precipitated sulphur (5 % w/w) (all from David Craig Galenicals Pty Ltd, QLD, Australia). Other ointment formulation excipients were triethanolamine (1 % v/w, Asia Pacific Speciality Chemicals Pty Ltd, NSW, Australia), and cod liver oil (10 % v/w, Gold Cross Biotech Pharmaceuticals Pty Ltd, VIC, Australia). The test and control ointments were prepared following Australian Pharmaceutical Formulary and Handbook guidelines for ointment preparation at the School of Pharmacy, University of Tasmania. The control formulation contained ketoconazole (2 % w/w) and the test formulation contained kunzea oil (20 % v/w). Emulsifying ointment was added to make it up to 100 %. Ointments were packed in 100 g jars and a tamperproof seal was attached to each lid. The ointments, control or test were assigned sequential code numbers according to a computer-generated randomisation list, which was kept securely by a staff member who was otherwise not directly involved with this study. Treatment allocation was concealed from the evaluating veterinarians and the other investigators until all horses had finished the study treatment period.

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The treatment of each horse, after the initial assessment, involved cleaning and drying of the affected pasterns without the use of antiseptic solutions. Crusts were removed. In a few cases, the horses required sedation for this process to be possible. Surgical scissors were used to remove hair from around each lesion. The ointment was then applied liberally, by the veterinarian, to each lesion and the surrounding areas. The horse carer was instructed to keep the pasterns clean and dry and to apply ointment to the lesions twice daily, as demonstrated by the veterinarian. The treatment was continued by the horse carer until the next assessment.

Assessment

The primary outcome measure was the total lesion area, which was the sum of the areas of all the pastern dermatitis lesions on an animal. Where a horse had more than one lesion, the largest lesion was termed the primary lesion. The lesion areas were measured by using a method similar to the acetate tracing technique (Gethin and Cowman, 2005). A sterile adhesive transparent sheet was placed over the wound surface and the lesion perimeter was traced using a fine-tipped permanent marker pen. The tracings were subsequently photocopied onto paper and the paper was cut along the line that defined the lesion border. The resultant paper cutout was weighed (to 0.1 mg) and its area, corresponding to the lesion area, was determined from the unit area mass of the paper.

Seven clinical signs associated with pastern dermatitis were identified. Each affected pastern was assessed for exudate, crusting, skin fissures, alopecia, skin excoriation, hypopigmentation and wheals. A 0-4 linear visual analogue scale (0 = none; l = some; 2 = mild; 3 = moderate and 4 = severe) was used. Scores were added to yield a 'lesion score' which had a possible maximum value of 28 per pastern. A total lesion score was obtained by adding together the lesion scores from each pastern. This was used as a secondary outcome measure.

One lesion, termed the target lesion, was selected by the veterinarian for taking pathology specimens. This was usually, but not always, the largest lesion present. A tissue sample (crust and/or hairmat) was taken and sent to be cultured for Staphylococcus spp., Dermatophilus congolensis, Microsporum spp., Trichophyton spp., and Malassezia pachydermatis. Exudate from the lesion was smeared onto two sterile glass slides that were sent for examination. All pathological testing was performed by Idexx Laboratories (Brisbane, Australia), a certified veterinary pathology laboratory, using standard methods. Cultures were grown on commercially prepared selective media. Smears were Gram-stained prior to microscopic examination.

The initial assessment was performed before any treatment. Follow-up assessment was performed after 7 days of treatment. Lesions were measured and scored as described above. In cases of complete resolution of pastern dermatitis signs, a skin scraping and hair sample were taken from the target lesion for microbial culture, and contact smears on sterile glass slides (x2) were obtained for microscopic examination. In cases that did not improve after 7 days, the treatment medication was switched to the alternative medication (crossover). In cases that improved but did not resolve after 7 days, treatment was continued using the allocated medication for up to 28 days. A further follow-up assessment was carried out after 28 days or earlier if complete resolution occurred. Lesions were measured and scored as before and samples were obtained for pathological testing, as described above.

A diary was given to horse carers for recording applications of ointment, and to record any adverse reactions. The compliance of horse owners/carers to the treatment protocol could not be rigorously confirmed. Carers were asked during the first follow-up visit whether they had applied ointment as instructed. The amount of ointment remaining after one week was checked visually by investigators. Treating veterinarians examined horses for adverse drug effects during the course of their follow-up assessments.

The study protocol was approved by the University of Tasmania Animal Ethics Committee.

Statistical analysis of results

All statistical analyses were performed using StatView 5.0 (SAS Institute Inc., Cary, NC, USA). For comparisons within test or control groups the Wilcoxon signed rank test was used. For comparison of values between the test and control groups the Mann-Whitney test was employed. The frequencies of distribution of the positive pathology results were analysed using the Chi-square test. For all analyses, values of P<0.05 were considered significant. All the data were reported as median (and range) or mean (± SD).

Results and Discussion

Study subjects

Thirty seven horses were recruited for this trial between December 2005 and May 2006, as shown in Table 4.1, of which 21 completed the study. The recruitment included 24 females and 13 males represented by 13 thoroughbreds, 10 Arabians, one American quarter, three ponies, four thoroughbred-cross breeds, four Arabian-cross breeds and two Warmbloods. The median duration of disease prior to enrolment was seven months. Baseline demographic and morphological features of the study population were statistically analysed and no relationship was found between disease severity (total lesion area) and age, gender, pastern colour, breed, disease duration or housing.

Among the 37 horses enrolled, 16 did not undergo an evaluation after seven days of treatment. A major reason for the high dropout rate was the reluctance of owners to pay for a veterinary visit after seven days, which accounted for six horses. Two owners suffered a horse-inflicted injury and did not continue with the study, which accounted for the dropout of seven horses. In one case the veterinarian was unable to attend two horses for their seven-day assessment. One horse was rejected from the study because of a deviation from the study protocol. A total of 21 horses underwent seven days of treatment with an assessment after this time period. In both test and control groups a comparable mix of horse breeds was present. There were no statistically significant differences between the dropouts and horses completing the trial, or between the two groups of horses completing treatment, in terms of gender, breed, housing conditions, pastern color, pastern affected or duration of condition.

Table 4.1. Baseline demographics of all the horses enrolled in the pastern dermatitis trial.

Gender Age Disease Pastern Breed Housing Pastern(s)

(years) duration colour affected

gelding 11-15 3 months white thoroughbred paddock HRa

mare >15 8 months white Arabian paddock FRb, FLc, HLd

mare >15 3 months white Arabian paddock HL, HR

mare 11-15 3 months white Arabian paddock FR

gelding ≤5 2 weeks white thoroughbred stabled HR

mare 6-10 1 month white thoroughbred stabled HL

mare >15 2 days black American quarter paddock HL

gelding ≤5 2 years white thoroughbred stabled HL

mare 11-15 5 years brown pony paddock HL

stallion 11-15 2 years white thoroughbred paddock HL

mare >15 1 month white thoroughbred stabled HL, HR

mare 6-10 3 weeks white Arabian paddock HR

mare >15 2 years white thoroughbred cross paddock HL, HR

mare 6-10 4 months white thoroughbred cross paddock FL, FR

gelding ≤5 2 weeks white Arabian paddock HR

mare ≤5 4 weeks white pony paddock FL

mare ≤5 4 weeks white pony paddock HR

gelding >15 NAe white thoroughbred cross paddock HR

mare >15 NA white thoroughbred cross paddock FL

mare ≤5 1 month white Warmblood paddock FL, HR

mare >15 5 months white Arabian paddock FL, FR, HR, HL

mare >15 7 months white thoroughbred paddock HR

mare >15 7 months white thoroughbred paddock FL, FR, HR

gelding >15 7 months white Arabian paddock HL, HR

mare 11-15 1 month white Warmblood paddock FL, HL

mare ≤5 1 year white thoroughbred stabled HL

gelding ≤5 1 month brown Arabian stabled FL

gelding ≤5 3 weeks white thoroughbred paddock HL

mare ≤5 3-4years white Arabian paddock HL

gelding ≤5 2 weeks white Arabian paddock HR

mare 6-10 1 month white thoroughbred paddock FL

gelding 11-15 2 months white thoroughbred paddock HR

mare ≤5 1 year white Arabian cross stabled HL

mare 11-15 5 months white Arabian cross stabled HL

mare 11-15 2 months white Arabian cross stabled FL, FR, HR, HL

gelding ≤5 3 years white Arabian cross paddock FL, FR, HR, HL

gelding >15 1 month white thoroughbred paddock HL

ahind right, bfront right, cfront left, dhind left, edata not available

Assessment

The results of the day zero and day seven assessments are summarised in (Table 4.2). Lesion areas of the test and control groups were not different on day zero (P>0.05, Mann-Whitney test).

Table 4.2. Comparison of pastern dermatitis lesion areas in cm2 and lesion scores (median and range) before and after 7 days of treatment with kunzea oil ointment (test, n=11) or control ointment (n=10)

Clinical parameter Day 0 Day 7

Total lesion score

Test 7(3-36) 1(0-9) < 0.01

Control 7(1-29) 7(0-17) NSb

Mann-Whitney testa NSb < 0.05

Total lesion area

Test 40(3-252) 0(0-34) < 0.01

Control 81(4-264) 70(0-143) NS

Mann-Whitney test NS < 0.05

Target lesion score

Test 4(2-12) 1(0-9) < 0.01

Control 4(1-14) 4(0-13) NS

Mann-Whitney test NS < 0.05

Target lesion area

Test 35(3-207) 0(0-34) < 0.01

Control 64(4-147) 39(0-143) NS

Mann-Whitney test NS < 0.05

Highest lesion score

Test 4(2-12) 1(0-9) < 0.01

Control 5(1-14) 4(1-3) NS

Mann-Whitney test NS < 0.05

Highest lesion area

Test 35(3-207) 0(0-34) < 0.01

Control 79(4-147) 39(0-143) NS

Mann-Whitney test NS < 0.05

aP-value, bnot significant (P>0.05)

On day seven, the control lesion area had not changed significantly. The lesion areas of the test group had decreased significantly (P<0.01) from a total lesion area of median value 40 cm2 (range 3-252 cm2) to 0 cm2 (range 0-34 cm2). The response of the test group was significantly greater than the response of the control group (P<0.01,Wilcoxon signed-rank test).

Lesion scores of test and control groups were no different on day zero. On day seven, the lesion scores of the control group had not changed significantly, however the lesion scores of the test group had decreased significantly (P<0.05, Mann-Whitney test) from a total lesion score median value of seven (range 3-36) to a median value of one (range 0-9). The response of the test group was significantly greater than the response of the control group (P<0.01,Wilcoxon signed-rank test).

Figure 4.1. A case of pastern dermatitis before treatment (A) and after three weeks of

treatment with kunzea oil ointment (B)

Of the 11 horses treated with test ointment, after seven days, seven were fully resolved with 100% decrease in lesion area. Four had improved, with a mean (± SD) decrease in total lesion area of 71±29%. Of the 10 horses treated with the control ointment, after seven days, two were fully resolved, two showed some improvement (with a mean (± SD) decrease in total lesion area of 23±6%) and continued with the same treatment, and six showed no improvement or their condition worsened. Of the six horses whose condition did not improve, five underwent crossover to the test ointment and one was lost to further follow-up. An example of a treatment outcome for one horse is illustrated in Figure 4.1.

Of the two horses that continued on the control ointment, neither was fully resolved after 28 days. One of these horses then underwent crossover to the test ointment. Of the total 6 horses that crossed over to the test ointment five were fully resolved within 28 days (mean time to healing was 14 days). The single treatment failure experienced an injury to the affected pastern and could not continue with treatment.

The four horses from the test group that did not fully resolve within seven days continued treatment for a further 21 days. After a total of 28 days, two horses were fully healed and the other two (both from the same premises) had marginal improvement. One of these had all four legs affected. Lesions fully healed on one leg after seven days, and on another two legs after 28 days, leaving one lesion unhealed. This lesion appeared to be resistant to treatment, having no decrease in area (from 11 cm2 to 13 cm2) over four weeks. No further investigation was performed on this

The pathology results are summarised in Table 4.3. The most commonly isolated microorganism was Staphylococcus aureus, which was present in 75% of lesion sites before the commencement of treatment, based on culture results.

Fungi were cultured from lesion sites in only a few cases. The presence of S. aureus was similar in both control and test groups at day zero. Follow-up pathology samples were obtained either upon full healing (lesion area reduced to 0 cm2), before crossover (when treatment did not reduce lesion area) or after 28 days of treatment (when treatment reduced lesion area but not to 0 cm2). In three control cases follow-up pathology samples could not be obtained. After the treatment period there was a significant decrease in the presence of cultured S. aureus in the test group compared with the control group (P<0.05, Chi-square test).

Discussion

Pastern dermatitis can lead to effects ranging from inconsequential to seriously debilitating. It was once thought to be primarily a consequence of mismanagement and neglect (Youatt, 1874). However, it is now acknowledged that many factors may play a role in the aetiology of the condition. These factors include environmental conditions and host-specific differences, with draught horses being the most susceptible, particularly those with feathering. Anecdotal reports suggest that pastern dermatitis tends to occur more frequently during seasonally wet periods, particularly if pasture grasses are tall and horses are exposed to prolonged periods of wetness. Standardbreds are often affected during spring when tracks are wet (Kahn, 2005). Draught horses working in muddy conditions are very susceptible. Horses kept on rubber meadows were found to have less severe symptoms of pastern dermatitis than those kept on soil or sand (Geburek et al., 2005). Exposure to sunlight also seems to play a role, with high levels of sunshine resulting in a higher incidence (Stannard, 2000). It has also been suggested that non-pigmented pasterns are more prone to the condition than coloured pasterns, due to photosensitization (Pascoe and Knottenbelt, 1999, Stannard, 2000), a comment that was supported by horse owners and veterinarians involved in the current study.

The current study assessed the efficacy of an ointment containing kunzea oil in the treatment of pastern dermatitis. There were several options for the control medication used in the study. A clinically proven standard pastern dermatitis treatment would have been the control of choice, but there does not appear to be such a product available on the Australian market. A placebo treatment was not considered appropriate on ethical grounds. An appropriate control treatment would have been the test ointment minus the kunzea oil component (vehicle only), since the ointment base contains excipients such as zinc oxide, salicylic acid and sulphur that would be expected to have some potential benefits. However, at the time of the study design the potent antifungal activity of kunzea oil had been identified and, given the potential involvement of fungi in pastern dermatitis, it was decided to include an antifungal agent in the control ointment. It was also considered, on ethical grounds, more appropriate to offer horse owners a control ointment with a greater potential for activity than a vehicle-only control. Ketoconazole (2%), which was included in the control formulation, has potent antifungal activity in topical applications. In addition ketoconazole has some anti-inflammatory and antibacterial activity (van Cutsem et al., 1991). This choice of control ointment allowed the relative importance of the purported major active ingredient of the test ointment, kunzea oil, to be determined. Also, some differentiation of the relative importance of its antifungal versus its antibacterial activities, in the treatment of pastern dermatitis, could be ascertained.

The results of the study clearly demonstrated the efficacy of the kunzea oil ointment in the treatment of pastern dermatitis in this particular cohort of horses. More than half the cases were completely cured and all cases improved, on the basis of clinical signs and lesion areas, after one week of treatment. Reports from horse owners indicated that in some cases lesions improved dramatically within a few days. By comparison, only two of the horses treated with the control formulation were cured after one week of treatment, two improved and six did not. Statistically, the kunzea oil formulation was significantly more effective than control, on the basis of lesion area reduction and improvement of lesion scores. Although treatment efficacy was not formally evaluated after the day seven assessment, the qualitative improvement of the horses that continued treatment with the kunzea oil formulation, particularly the cases that crossed over from the control group after one (n=5) or four (n=1) weeks, supports the conclusion that the kunzea oil ointment was an effective treatment in this trial.

Pathological screening demonstrated staphylococcal involvement in most pastern dermatitis cases, with Staphylococcus aureus present in 15 cases and a coagulase-negative Staphylococcus sp. in three cases, two of these being mixed staphylococcal cultures. Only four from 20 cases screened did not culture a Staphylococcus sp. from a crust or hairmat sample. The major Gram-stain findings were of Gram-positive cocci, consistent with primarily staphyloccal infection, in 13 cases. Culture of samples from healed pastern dermatitis cases (when the lesion area was 0 cm2), including the two control cases that were cured, all resulted in negative staphylococcal and fungal culture. Gram-stain microscopic examination of smears also showed a reduction in the number of staphylococci, there being only two cases for which Gram-positive cocci were observed following treatment. It is apparent from these results that S. aureus played an important role in the pastern dermatitis cases of this study cohort - if not in the initiation of the underlying disease, then at least in the progression of the lesions. S. intermedius has previously been implicated in a case of vasculitis (Risberg et al., 2005) and systemic antibiotic therapy was effective in exacting a cure. We have recently determined that kunzea oil is potently bactericidal towards S. aureus and a range of other Gram-positive cocci and bacilli, as well as having activity against a range of yeasts and dermatophytes, including Trichophyton spp. and Microsporum canis (unpublished findings). The potent activity of kunzea oil against staphylococci probably underlies its efficacy in the treatment of pastern dermatitis cases in this study. The antifungal activity of kunzea oil may also contribute to its efficacy where fungi may play some part in the disease pathogenesis, although fungal involvement in the cases of this study appeared to be less important than bacterial infection.

The day zero median value of the total lesion area in the control group was 81 cm2 compared with 40 cm2 in the test group. These values were not statistically different, and the lesion severity scores were very similar for the groups. Treatment outcome did not appear to relate to the initial lesion area. For example, the horse with the lesion having the second-greatest individual area (147 cm2) was completely healed after seven days' treatment with the control formulation. There were some cases (2 out of 10) that appeared to respond to treatment with the control formulation. These positive outcomes may have been due to some anti-inflammatory, antibacterial and/or antifungal activity of the control formulation.

This study was designed as a blinded study. However, the distinctive odour of kunzea oil made it possible for some horse owners to identify the kunzea oil formulation. This did not affect the assignment of medications, as the randomisation schedule was predetermined and medication jars were secured with a seal to prevent disclosure of the contents before admission of a horse to the study. Six veterinarians were involved in this study, introducing the potential for observer variability. However, each horse in the study was assessed by only one veterinarian, so that overall any variability would have been between cases and not within cases, thus limiting any impact on the statistical evaluation of the study results.

The study assessed the treatment of 21 cases from a narrow population base, mostly from Southern Tasmania. Although the outcomes of the trial clearly demonstrated a positive response to treatment with kunzea oil ointment, the level of response may not be the same in horses from other environments, where the disease aetiology may be different. Also, the ointment was not tested on any draught horses in which pastern dermatitis can be especially difficult to manage. Nevertheless, this study represents the first formal trial of a potential veterinary medication that demonstrates effectiveness in the treatment of pastern dermatitis.

In conclusion, treatment of pastern dermatitis with a formulation containing kunzea oil, a potent antibacterial essential oil, cured most cases within seven days and was more effective than the control formulation containing ketoconazole. The kunzea oil ointment was a safe, fast-acting and effective treatment for pastern dermatitis in the study cohort. If the results obtained in this trial prove to be generally applicable to the broader horse population, the kunzea oil ointment may offer horse owners a convenient and effective treatment option for non-severe pastern dermatitis.