Author
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Rosebrough, Robert |
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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 4/10/2000 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: The role of the thyroid axis is one of the more controversial areas in the study of growth and metabolism in the broiler chicken. Although chemical hypothyroidism, caused by either propylthiouracil (PTU) or methimazole, decreased growth, artificial changes in thyroid hormone levels did not always change growth predictably. While dietary T$-(3)$ and T$-(4)$ 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 form previous studies is any information concerning birds' ability to recover from thyroid hormone perturbations (inhibition of T$-(3)$ production). Hubbard, male broiler chickens were fed diets containing 120, 180 or 240 g protein $\pm$1 mg methimazole/kg diet form 7 to 28 d of age. Birds were then fed 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. However, dietary methimazole attenuated this effect, resulting in a common rate that was similar to that attained in the birds fed the highest level of protein without methimazole. In contrast, birds fed methimazole form 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. Observations at 49 d suggest that permutations in the thyroid of the young bird may substantially change metabolism in later life. |
