Effect of supplementing synthetic amino acids in low-protein diet and subsequent re-feeding on growth performance, serum lipid profile and chemical body composition of broiler chickens

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 Med and Lys supplementation and 3) the Low-CP diet supplemented with Met and Lys (Low-CP + Med + 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.