Submitted to: Journal of Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/6/2005
Publication Date: 5/31/2005
Citation: Carew, L., McMurtry, J., Alster, F. 2005. Effects of lysine deficiencies on plasma levels of thyroid hormones, insulin-like growth factors I and II, liver and body weights, and feed intake in growing chickens. Poultry Science. 84:1045-1050. Interpretive Summary: In animal diets the essential amino acid lysine is frequently limiting, thus must be supplemented into the diets. Deficiencies in lysine negatively affect growth and feed intake in chickens. Thyroid hormones and the insulin-like growth factors are essential for normal growth and metabolism in poultry. These experiments were conducted to determine whether graded decreases in dietary lysine elicited changes in circulating thyroid hormones and insulin-like growth factor concentrations in growing chickens. The results of this study demonstrate that the reduction in growth caused by lysine deficiency is not directly associated with changes in circulating hormones. The growth deficiency is most likely the result of reduced feed intake in lysine-deficient chicks. Further study is necessary to determine what components of the appetite regulatory system are altered under lysine limiting situations. The results of this study will be of interest to other scientists.
Technical Abstract: A severe lysine (Lys) deficiency alters thyroid hormone metabolism in chickens but insulin-like growth factor (IGF) has not been studied. We therefore measured the effect of mild to moderate Lys deficiencies on changes in plasma levels of these hormones. Adequate (1.10%) and deficient (0.88, 0.66 and 0.53%) Lys was fed to broiler chicks 9- 23 d of age. Groups fed the control diet (1.10% Lys) were pair-fed daily with each deficient group. Graded decreases in feed intake occurred as the deficiency worsened and were significantly different from the free-fed control with 0.66% and 0.53% Lys. Growth was significantly slower with each Lys deficiency compared to the free-fed control and was always significantly less compared to pair-fed controls. Plasma triiodothyronine (T3) increased in chicks fed 0.88% and 0.66% Lys but not 0.53% compared to full-fed control. However, in deficient chicks receiving 0.66% and 0.53% Lys, T3 was significantly higher compared to pair-fed controls. Plasma T4 was unaffected. Liver weights were significantly smaller at each Lys deficiency, but differences disappeared when expressed relative to body weight. Plasma IGF-I was significantly lower with 0.53% Lys, but this was solely a consequence of restricted feed intake. Plasma IGF-II levels were unaffected. No correlations were evident between thyroid hormones and IGF-I or -II values. We conclude that the primary effect of a Lys deficiency is an elevation in plasma T3 without an accompanying change in T4. No effect of the Lys deficiency per se on plasma IGF-I and -II, and relative liver weights was found.