Effect of long-term oral administration of thyroxine on morphology of the gastrointestinal tract in broiler breeder hens

Published data on 4-week-long administration of extra thyroxine (T4</sub>) in broiler breeder hens to alleviate the cold-induced ascites in their offspring suggested that long-term maternal hyperthyroidism would affect the gastrointestinal tract morphology. Broiler breeder hens (n=70) were reared in individual cages and allotted to control and hyperthyroid groups (five replicates of seven hens each). Thyroxine, dissolved in water, was orally administered to the hyperthyroid group (0.3 mg T4</sub>/bird/day) for 100 days and the control group received an equal volume of drinking water. At the end of the experiment (64 week of age), two birds per replicate (20 hens in total) were selected for histological evaluation of the gastrointestinal tract. Thyroxine treatment resulted in an increase in plasma concentration of T4</sub>; however, triiodothyronine (T3</sub>) level was not affected. The results of this study showed that long-term administration of T4</sub> had no adverse effects on the gastrointestinal morphology in broiler breeder hens; therefore, long-term maternal T4</sub> administration may be recommended as a treatment to reduce the ascites incidence in the progeny. However, further studies are needed to confirm this recommendation as a preventative treatment in reducing the ascites incidence.