The natural history of the obese strain of chickens - An animal model for spontaneous autoimmune thyroiditis

Chickens of the Obese strain (OS) are hereditarily affected with spontaneou s autoimmune thyroiditis that resembles Hashimoto's thyroiditis of humans i n clinical, histopathological, serological, and endocrinological aspects. L n this review, the natural history of the OS, reflecting the development an d maintenance of the stock and its improvement of productivity over many ye ars at Cornell University, is summarized. To underline the value and useful ness of this animal model, the concept of the multifactorial pathogenesis o f autoimmune diseases, which was mainly established at the University of In nsbruck, Austria, is briefly outlined. This detailed analysis on the natural history of the OS was only made feasi ble by the availability of four decades of records on this chicken line at Cornell University. The report starts with the initial occurrence of a few pullets within the Cornell. C-strain (CS) flock that showed obesity, long a nd silky feathers, and small body size,which, therefore, caused these birds to look notably different than the other CS birds. Experimental findings i ndicated an autoimmune basis for these characteristics, and the objectives of matings were initially focused on increasing the number of obese individ uals for studies on the etiopathology and the mode of inheritance. In subse quent years, matings were directed toward increasing the penetrance and sev erity of the obese trait in the population. In recent years, the reproducti ve capability of the obese stock was improved by mating only the best breed ers of the population in terms of body weight, egg weight, egg production, fertility, hatchability, and the expression of the obese phenotype. Housing conditions for OS chickens at Cornell and the qualification standards and selection procedures for breeders are described in detail, and results of b lood typings are shown. A specific recent finding in OS hens is the high in cidence of residues of the right Mullerian duct with cyst formation.