SUPPLEMENTAL THYROID-HORMONES AND MOLTING IN TURKEY BREEDER HENS

The objective of the current study was to determine whether thyroid ph ysiology may affect molting time in turkeys. Two trials using approxim ately 144 hens were conducted to elucidate thyroidal factors that limi t the molting process. Thyroid hormones or a thyroid blocker (thiourac il) were given to the hens during a molt by supplementing the diet wit h thyroxine (T-4), triiodothyronine (T-3), or thiouracil. Supplementin g with T-4 reduced the number of days to return to egg production, whe reas supplementing with thiouracil or T-3 prolonged days to first egg. The observations support previous suggestions of separate functions f or T-3 and T-4 during molting. As had been observed many times previou sly, the feeding of thiouracil delayed the molt but did not completely stop the molting process. The hens fed thiouracil returned to 50% egg production nearly 10 d after the control group, whereas T-3 prolonged the return to 50% egg production nearly 1 wk later. The data indicate the endogenous low levels of T-4, but not T-3 in modern strains of tu rkeys may contribute to a relatively longer molting period of turkey b reeder hens induced to molt out of season.