This study was conducted to evaluate the e ects of adding methionine (Met) to low-protein diets and subsequent re-feeding on the growth performance, serum lipid profile, body composition and carcass quality in male broiler chicks during days of age. During the starter-grower period (days of age),

This study was conducted to evaluate the effects of supplementing methionine (Met) and lysine (Lys) in low protein (Low-CP) diet during 1-21 days of age, and subsequent re-feeding with conventional diet during 22-42 days of age on growth performance, serum lipid profile, chemical body composition and carcass quality of broiler chickens. During 1-21 days of age (starter period), 480 male broiler chicks (Ross 308) were divided into three treatments and given the following diets: 1) conventional diet group (all nutrients met the requirements of the strain), 2) Low-CP diet without Met and Lys supplementation and 3) the Low-CP diet supplemented with Met and Lys (Low-CP + Met + Lys). During the finisher period (22-42 days of age), all groups were fed a diet containing the same nutrients in accordance with the recommendations of the strain. At 21 days of age, Low-CP + Met + Lys diet showed significantly better growth performance and breast meat yields than those of the Low-CP diet group. Feed and protein intake of the chicks fed conventional diet was significantly higher than both of the other groups (P＜0.01), whereas Low-CP + Met + Lys diet clearly improved protein efficiency (P＜0.01). Feeding Low-CP diet increased abdominal fat content and body energy content (P＜0.05), while the supplementing synthetic amino acids slightly decreased the fat content. Triglyceride, very low density lipoprotein (VLDL) and T3 hormone in blood were significantly increased in Low-CP + Met + Lys diet group compared to the conventional diet (P＜0.05). After the re-feeding phase, feeding Low-CP diet groups were unable to compensate body weight equal to the conventional diet, although a compensation of FCR was observed. Feeding Low-CP + Met + Lys diet showed the same breast meat yield compared to the conventional diet, but abdominal fat, triglyceride and VLDL in blood were significantly increased (p＜0.05). In conclusion, supplementing Met + Lys in Low-CP diet improved performance production, but was still inferior to the conventional diet.