Hereditary hypothyroidism in the domestic fowl.

OPULATIONS of fully pedigreed chickens often contain individuals which ’deviate considerably in one or more respects from the average for the flock. When pedigrees reveal close genetic relationship among those similarly affected, further studies are warranted. Such was the case for the trait now recognized as hypothyroidism. Affected 5 %-month old White Leghorn pullets, which were somewhat smaller in skeletal size than normal, possessed long silky feathers, and were rather obese, began to lay before there was a development in size and redness of the comb. Reported egg production by two such birds had to be witnessed in person by the author before he would believe! The fact that the few such individuals all came from one of three strains and that they often were halfor full-sisters prompted a study to determine the role of heredity in the development of this trait. Individuals with similar phenotype have now been observed in several other unrelated stocks. It is apparent that the trait may be more common than at first beljeved but, because of the associated defects in normal physiology, affected individuals rarely survive to reach the age of maturity.