Reproductive tissue activity in hypothyroid or heat stressed hens

The ability of the reproductive tract of the White Leghorn hen under heat stress or methimazole thyroid blockage to assimilate 32P was examined. Both treatments increase the uptake of 32P by the shell gland and egg shell but only heal stress increases 32P uptake by the ovaries and reduces shell thickness. The greater shell thinness under the heat stress is related to an increased deposition of phosphate in the shell. Gilbert (1967) has reported an increased serum calcium, due to calcification inhibitions by phosphate, leading to an increased gonadotropin secretion. Thyroid blockage appears to stimulate TSH and gonadotropin LH secretion but in the absence of phosphate inhibition of calcification shell thickness is not affected. It is also speculated that hypothyroidism does not stimulate FSH secretion and therefore ovarian tissues is not activated by this condition.