Long-term effects of thyroxine-induced hyperthyroidism on the histological attributes of the oviduct in broiler breeder hens

Abstract

A 4-week-long administration of extra thyroxine (T₄) in broiler breeder hens was recommended to lower the cold-induced ascites incidence in the progeny chicks. A hypothesis was tested that the long-term-induced hyperthyroidism might influence the histological traits of oviducts in the exposed hens. A total of 70 47-week-old Cobb 500 breeder hens were randomly allotted to two treatment groups (5 replicates of 7 hens each), including the control (CON) and hyperthyroid (HYPER). Thyroxine (T₄) was orally administered to the HYPER group (0.3 mg/bird day⁻¹) for 100 successive days; whereas the CON group received the drinking water only throughout the trial. At 64 weeks of age, two birds per replicate were cervically dislocated and their oviducts were removed for histological sectioning and staining. Results showed that secretory cells were detected in the anterior infundibulum and the number of secretory cells in the hyperthyroid hens was smaller than that of the control group. Thyroxine-treated hens recorded a decreased number of tubular glands in the magnum as compared to that of the control hens. The circular muscle layer of isthmus showed a more regular arrangement in the control in comparison with the T₄-treated hens. Additionally, the number of uterine tubular glands in the hyperthyroid group was lower than that of the counterparts. A decline in the vaginal epithelial thickness in the hyperthyroid hens was also recorded as compared to the control birds. Overall, the long-term administration of thyroxine was associated with considerable impacts on different parts of the oviduct. The question as to what extent the long-term maternal hyperthyroidism might affect the basal metabolic rate, egg production, fertility rate, duration of fertility, hatchability, and the chick quality remains open to make a final decision on exploitation of this preventative treatment to diminish the ascites incidence in progeny chicks.

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