Clxxxv. the Action of Thyroxine on the Milk and Milk-fat Production of Cows. by William

A PREVIOuS study of the effects of thyroidectomy and thyroid feeding on the lactation of cows has shown that the thyroid gland has a marked influence on the production of milk and milk-fat by the cow [Graham, 1934]. Rises in milk and milk-fat production were shown when desiccated thyroid glands were added to the diet either of thyroidectomised animals or normal animals which were past the peak of the lactation cycle. Milk-fat production appeared to be more closely related to the action of thyroid than was milk secretion. The experiments suggested some relationship between milk-fat formation and metabolic rate. In investigating this action more fully, it was thought advisable to pin it down, if possible, to thyroxine. If thyroxine were actually shown to reproduce the results found after feeding the dried glands, there are several possible mechanisms by which its activity in this direction could be exercised. If it is an effect directly due to changes in metabolic rate, it ought to be possible to bring about a similar effect with nitrophenols.