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Hypothyroidism: An Early Sign of Vitamin A Deficiency in Chickens¹

Department of Animal Sciences and Department of Pathology, Colorado State University, Fort Collins, CO 80523

The effect of a marginal vitamin A deficiency on thyroid function was investigated in chicks gaining weight. This study examined the hypothesis that hypothyroidism is one of the earliest manifestations of hypovitaminosis A in chicks. Day-old Leghorn cockerels were fed vitamin A-adequate and deficient diets. Blood vitamin A levels were reduced in the deficient chicks by 3 weeks of age. Body weight gains were less in the 5-, 6-, 7- and 8-week-old A-deficient chicks than in controls. Compared to controls, vitamin A-deficient chicks were characterized by thyroid follicle hypertrophy by 4 weeks, heavier thyroids as a percent of body weight at 5 weeks, less serum thyroxine (T₄) at 7 weeks and lower serum triiodothyronine (T₃) and T₄ at 8 weeks. These results indicate that one of the earliest signs of vitamin A deficiency in chicks is hypothyroidism.

KEY WORDS: • vitamin A deficiency • hypothyroidism • thyroxine • triiodothyronine

¹ Supported in part by BASF, Ludwigshafen/Rhein., West Germany.

Manuscript received 7 May 1984.

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