Gerber V Baleri D Klukowska-Rötzler J Swinburne JE Dolf G 2009 BACKGROUND Mode of inheritance of equine recurrent airway obstruction (RAO) is unknown. HYPOTHESIS Major genes are responsible for RAO. ANIMALS Direct offspring of 2 RAO-affected Warmblood stallions (n = 197; n = 163) and a representative sample of Swiss Warmbloods (n = 401). METHODS One environmental and 4 genetic models (general, mixed inheritance, major gene, and polygene) were tested for Horse Owner Assessed Respiratory Signs Index (1-4, unaffected to severely affected) by segregation analyses of the 2 half-sib sire families, both combined and separately, using prevalences estimated in a representative sample. RESULTS In all data sets the mixed inheritance model was most likely to explain the pattern of inheritance. In all 3 datasets the mixed inheritance model did not differ significantly from the general model (P= .62, P= 1.00, and P= .27) but was always better than the major gene model (P < .01) and the polygene model (P < .01). The frequency of the deleterious allele differed considerably between the 2 sire families (P= .23 and P= .06). In both sire families the displacement was large (t= 17.52 and t= 12.24) and the heritability extremely large (h(2)= 1). CONCLUSIONS AND CLINICAL RELEVANCE Segregation analyses clearly reveal the presence of a major gene playing a role in RAO. In 1 family, the mode of inheritance was autosomal dominant, whereas in the other family it was autosomal recessive. Although the expression of RAO is influenced by exposure to hay, these findings suggest a strong, complex genetic background for RAO. application/pdf https://sonar.ch/global/documents/162565 eng info:eu-repo/semantics/altIdentifier/doi/10.1111/j.1939-1676.2009.0292.x info:eu-repo/semantics/altIdentifier/pmid/19645845 info:eu-repo/semantics/openAccess Journal of veterinary internal medicine. - 2009 Animals Genetic Predisposition to Disease Horse Diseases Horses Lung Diseases, Obstructive Models, Genetic Mixed inheritance of equine recurrent airway obstruction. http://purl.org/coar/resource_type/c_6501