Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 15, 2000
Publication Date: N/A
Technical Abstract: The thyroid axis is one of the more controversial areas in growth and metabolism of the broiler chicken. Although chemical hypothyroidism decreased growth, artificial changes in thyroid hormone levels did not always change growth predictably. While dietary T3 and T4 decreased body weight and feed efficiency of chickens, daily injections of thyroid releasing hormone (TRH) improved growth and increased plasma thyroid hormone concentrations. What is lacking from previous studies is any information concerning recovery from inhibition of T4 production. Male broiler chickens were fed diets containing 120, 180 or 240 g protein ñ 1 mg methimazole/kg diet from 7 to 28 d of age and then a diet containing 180 g protein from 28 to 49 d of age. Birds were killed at 28 and 49 days to 1) determine effects of treatments at 28 d and 2) determine carry over effects of these treatments. In vitro lipogenesis was inversely related to dietary protein levels in control birds at 28 d. Dietary methimazole attenuated this effect, resulting in a common rate similar to that attained in the birds fed the highest level of protein without methimazole. In contrast, birds fed methimazole from 7 to 28 d had greater lipogenic rates at 49 d than did their control counterparts. It is unclear at this time if observations noted at 28 d can be traced to reduced feed intake or to changes in thyroid status. Previous pair-feeding studies from this laboratory confirmed that differences in metabolic parameters caused by differences in dietary protein were not attenuated by limit feeding. Observations at 49 d suggest that permutations in the thyroid of the young bird may substantially change metabolism in later life.