Population genetic analysis of dermatitis digitalis in South German Draught horses

The objective of the present study was to examine the involvement of genetic components in the occurrence of dermatitis digitalis in South German draught horses. In the context of this study 455 horses were clinically examined and their individual housing and management conditions were documented. Furthermore, thickness of the neck skin was measured in the animals by using a cutimeter. This study could demonstrate that 58.5 % of the 455 examined horses were affected by dermatitis digitalis. Regarding the sex distribution, the stallions (66%) were more often affected by dermatitis digitalis than the mares (57.5 %). The most frequently observed forms of dermatitis digitalis were crusted or hyperceratotic and hyperplastic. It could further be stated that at the age of 2.5 to 6 years 53.2 %, in the age of 7 to 12 years 59.3 %, and older than 12 years even 72.5 % of the animals showed signs of dermatitis digitalis. Not well managed and inhygenic conditions were related to a higher frequency of dermatitis digitalis. The heritabilities estimated for the prevalence of dermatitis digitalis using several animal models were between h2 = 0.14 and 0.20. The heritability estimate for the number of legs affected by dermatitis digitalis reached a value of h2 = 0.17. Thickness of neck skin and prevalence of dermatitis digitalis were genetically correlated at rg = 0.54. Furthermore, a positive additive genetic correlation was found between the occurrence of chorioptes equi and dermatitis digitalis. However, the additive genetic correlation between the prevalence of dermatitis digitalis and white coloured fetlocks, length or density of the fetlock hairs was close to zero. The estimated heritabilities indicate that breeding programs may be suitable to reduce the prevalence of dermatitis digitalis.

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