This experiment was conducted to evaluate the effects of dietary methionine (met) levels on thyroid function, egg characteristics and protein and energy efficiency of laying hens. A total number of 216 commercial laying hens at 23 weeks of age were randomly allocated to six treatments (four replicates with nine birds in each), and fed 6 dietary have deficiency in met supplement (0.24, 0.29, 0.34, 0.39, 0.44 and 0.49% met). With increasing dietary met level from 0.24 to 0.49%, plasma triiodothyronine (T3) showed an inverted U relationship. Plasma thyroxin (T4) was similar between all treatments. Protein and energy efficiency were increased by increasing dietary Met levels. Egg shape index was significantly higher and lower with 0.29 and 0.39% met levels in diet, respectively. Egg surface area and unit surface shell weight increased by increasing dietary met level from 0.24 to 0.49%, and shell ratio decreased linearly. Shell weight increased significantly by increased met level of diet to 0.34%. Albumin index and Haugh unit were significantly lower in hens which fed the three higher levels of met (0.39 to 0.49%). It is concluded that met deficiency alters normal thyroid hormone metabolism, but the effect was dependent on the degree of deficiency. Furthermore, optimal supplementation of met in diets deficient in met, could improve egg quality of laying hens.
Key words: Metionine, egg characteristics, triiodothyronine, thyroxine, laying hens.
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