Effects of long-term hyperthyroidism on body weight, egg production and reproductive traits in breeder hens

The aim of this experiment was to study the effects of long-term induced hyperthyroidism on the body weight and egg production. In addition the relationships between hyperthyroidism and some reproductive parameters were studied. A total of seventy 47-week-old Cobb 500 breeder hens were randomly allotted to two treatment groups (5 replicates of 7 hens each). Thyroxine was orally administered to the hyperthyroid group (0.3 mg/bird/day) for 100 consecutive days during which the body weight and egg production were recorded on a weekly basis. Effect of hyperthyroidism on plasma T4 levels was significant; but, the T3 level was not affected. Results indicated a significant decreasing effect of thyroid hormones on body weight. Thyroid hormones had no effect on egg production; however, the treatment × time (wk) interaction effect was significant on egg production. Ovarian and oviductal weight were not different between the control and hyperthyroid hens. Administration of thyroxine to breeder hens decreased the diameter of F1 follicles.