A genetic study of summer eczema in Icelandic horses

Sammanfattning: Several horse breeds around the world have shown sensitivity to biting insects. The horses seem to be particularly sensitive to certain species of the genus Culicoides. The main reaction to the insects' bites is itchiness and some horses itch until wounds appear. In Sweden and the rest of Europe many breeds have been observed to have the problem and as regards Icelandic horses this phenomena is widely discussed. It has been shown that horses exported from Iceland to continental Europe as adults have higher disease prevalence. These horses have less chance to develop a normal immune defense to Culicoides, since no Culicoides have been found in Iceland. Nevertheless, a certain proportion of Icelandic horses born outside Iceland are also affected by the disease, which in Sweden is known as summer eczema. The aim of this study was to estimate genetic parameters for severity of summer eczema in Icelandic horses born in Sweden. The study is based on information from a questionnaire sent to owners of Icelandic horse in Sweden during the summer of 2005, with questions regarding the status of their horses' eczema. The questionnaire was sent to owners of Swedish born horses after 33 selected stallions. The result is based on the information about 825 horses. A total of 8 % of the Swedish born horses were affected with summer eczema. Affected dams were more likely to have offspring with eczema, compared with healthy dams. The heritability was estimated at 0.20 ± 0.1 using a sire model and at 0.19 ± 0.1 using an animal model. The fixed effects included in the model were age and geographic location of the horse at present time. Age did not seem to be of significance (p>0.05) for the trait, whereas geographic location on the other hand showed to be significant (p< 0.05) for whether the horse develops eczema or not.