TDK conference 2013

Melanoma is commonly seen in old, grey horses and reaches approximately 80% prevalence over age of 15 years.

Our aim was to screen the prevalence and the severity of melanoma between all the horses with grey hair-coat in an Arabian and Shagya-arabian breeding farm in Hungary, and compare our results to the current international literature findings. We also planned to develop a simple, easy-to-use protocol for this issue.

Our protocol consists of: inspection and palpation of the predilection sites, measurement and description of the exact location of the found tumours. Then continuing the examination of the affected horses with body condition scoring, rectal examination in certain cases, complete blood count, and blood biochemistry test to detect the possible signs of paraneoplastic syndrome. Based on the number, size and ulcerativeness of the surface, the individuals were classified into 6 grades according to the grading system publicated by Desser et al. in 1980. These important datas are planned to use in a fellow-up study in the future. We also performed biopsy or fine needle aspiration in a few uncertain cases.

We found that 28 (26,9%) of 104 examined Shagya-arabian individuals (age between 3 and 28 years, mean age 7,8 years) were affected, of which 6 with grade 1, 8 with grade 2, 7 with grade 3 and also 7 with grade 4. We didn’t detect any grade 5 horse. 10 out of 13 individuals (76,9 %) of Shagya-arabians were affected with melanoma over the age of 15 years.

In the group of Arabian horses, we examined 40 horses, their age were between 3 and 20 years, mean age was 8,40 years. Five Arabian horses (12,5%) had melanoma, all of them were classified as grade 2. 3 out of 6 horses (50 %) in the aged (>15 years) group were diagnosed with melanoma, while only 5.88% were affected in the younger (<15 years) age group.

According to our results, prevalence of melanoma in Shagya-arabian and Arabian breeds is less than reported in previous studies in other horse breeds, although we examined a smaller population, and significant number of individuals involved in this study were under 15 years old. If we consider only horses older than 15 years, the prevalence of melanoma between Shagya-arabians is approaching to the data in the international literature, while in the Arabian population is still much lower. There was no correlation between age and severity of illness in Arabians, but we could see it in the Shagya-arabian group, where the aged individuals were more affected. Since these horses were kept under the same circumstances and all of them were grey hair-coated, the difference in the disease prevalence in the two related breeds might be explained by a different genetic background.