Objective - To assess heritability and mode of inheritance for hereditary equine regional dermal asthenia (HERDA) in Quarter Horses. Animals: 1,295 horses with Quarter Horse bloodlines, including 58 horses affected with HERDA. Procedure - Horses were classified as affected or unaffected or as undetermined when data were insufficient to assess phenotype. Pedigree data were analyzed to determine the probable mode of inheritance. Heritability was estimated by use of Bayesian statistical methods. Results - Heritability (mean ± SD) of HERDA was estimated to be 0.38 ± 0.13, with both sexes having an equal probability of being affected. Results for evaluation of the pedigrees were consistent with a single Mendelian autosomal recessive mode of inheritance. Conclusions and clinical relevance - HERDA in Quarter Horses is an inherited disease, and affected horses are more likely to produce affected offspring. An autosomal recessive mode of inheritance should be considered by people making breeding decisions involving Quarter Horses when a first-degree relative has been confirmed with HERDA or has produced affected offspring. In addition, breeders whose horses have produced affected offspring can reduce the likelihood of producing affected horses in the future by avoiding inbreeding.
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