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 spontaneous autoimmune thyroiditis that resembles Hashimoto's thyroiditis of humans in clinical, histopathological, serological, and endocrinological aspects. In this review, the natural history of the OS, reflecting the development and maintenance of the stock and its improvement of productivity over many years at Cornell University, is summarized. To underline the value and usefulness of this animal model, the concept of the multifactorial pathogenesis of autoimmune diseases, which was mainly established at the University of Innsbruck, Austria, is briefly outlined. This detailed analysis on the natural history of the OS was only made feasible 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 and silky feathers, and small body size, which, therefore, caused these birds to look notably different than the other CS birds. Experimental findings indicated an autoimmune basis for these characteristics, and the objectives of matings were initially focused on increasing the number of obese individuals for studies on the etiopathology and the mode of inheritance. In subsequent years, matings were directed toward increasing the penetrance and severity of the obese trait in the population. In recent years, the reproductive capability of the obese stock was improved by mating only the best breeders 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 blood typings are shown. A specific recent finding in OS hens is the high incidence of residues of the right Mullerian duct with cyst formation.