ON THE RELATION BETWEEN THYROID AND SEX GLAND FUNCTIONING IN THE BROWN LEGHORN FOWL

¹ Institute of Animal Genetics, University of Edinburgh

Of 5 thyroidectomised pullets raised to maturity 2 began to lay eggs at an age average for the flock; at the same time others exhibited certain morphological criteria associated with egg production although they did not lay. In all the experimental females sexual growth of the comb was completely inhibited.

In males the repressive action of the operation on the gonads was more pronounced; only the initial phases in spermatogenesis were completed and mature sperm were never found. Sexual growth of the comb was checked in the young experimental males and regression in the size of the comb was marked in the mature cocks.

Replacement therapy, using dried thyroid substance orally, induced growth of the comb in both sexes and initiated egg production in the females tested.

Comb growth ensued in 2 experimental females injected with a male hormone preparation, indicating that the absence of sexual growth in this organ was actually due to the deprivation of gonad secretion and not to a lack of sensitivity of comb tissues.

The differential response of the two sexes to the loss of thyroid tissue is discussed in relation to a postulated pituitary-thyroid-gonad mechanism.