This study was conducted to evaluate the effects of supplementing methionine (Met) in a low-protein (Low-CP) diet during d 11 to 24 and subsequently feeding with a low-metabolizable energy diet (Low-ME; -75 kcal/kg) or a normal ME diet during d 25 to 42 on the productive performance, blood chemical profile, and lipid metabolism-related gene expression of broiler chickens. The 1,600 broiler chicks were divided into 5 groups as follows: 1) Normal CP, then Normal ME; 2) Low-CP, then Normal ME; 3) Low-CP, then Low-ME; 4) Low-CP+Met, then Normal ME; and 5) Low-CP+Met, then Low-ME. During d 11 to 24, the growth performance of the control group was better than those of the other groups (P < 0.01). In Low-CP diets, the addition of Met resulted in an improvement in the growth performance, breast meat yield, protein conversion ratio, plasma total protein, and albumin (P < 0.01). Moreover, the supplementation significantly increased the plasma triglyceride content (P < 0.01). Feeding Low-CP or Low-CP+Met diets increased the abdominal fat content compared to the control group (P < 0.01). Feeding the Low-CP+Met, then Normal ME (d 25 to 42) resulted in compensation in the feed conversion ratio (FCR), protein conversion ratio, and energy conversion ratio equal to or better than the control group (P < 0.01). The body weights of birds fed Low-CP diets were still inferior to the control group (P < 0.01), except in the Low-CP+Met group followed by the normal ME diet. Feeding with the Low-ME diet tended to decrease the expression of the carnitine palmitoyl transferase I gene in the liver (P = 0.08). In conclusion, supplementing Met in the Low-CP diet during the grower period and subsequently feeding with a control diet improved the feed and protein conversion ratios, reduced fat accumulation, and reduced the production cost of broiler chickens with regard to fat deposition compared to the control diet.

The effects were investigated of supplementing methionine (Met) in a low-crude protein diet (Low-CP+Met) during Days 11–24 post-hatch and subsequent feeding with a low-metabolisable energy diet (Low-ME; –0.31 MJ/kg) during Days 25–42 on the productive performance and blood chemistry profile of broiler chickens. The 1600 broiler chicks were divided into four groups and fed as follows: (1) Control diet; (2) Low-CP (Met deficiency) diet during Days 11–24, then re-feeding with conventional diet; (3) Low-CP+Met diet during days 11–24, then re-feeding with conventional diet; and (4) Low-CP+Met+Low-ME diet (Low-CP+Met diet during Days 11–24, then re-feeding with Low-ME diet). During Days 11–24, the growth performance of the Control group was better than the other groups (P < 0.01), although the Low-CP+Met diet improved bodyweight, feed conversion ratio and improved the protein conversion ratio compare to the Low-CP group (P < 0.01). During the re-feeding phase (Days 25–42), reducing the dietary energy resulted in better growth performance and a better protein conversion ratio and energy conversion ratio than in the Control group (P < 0.05). Triglyceride, very low-density lipoprotein, low-density lipoprotein-cholesterol and total cholesterol in serum were higher, and non-esterified fatty acid was lower in the Control group than those of the Low-CP+Met+Low-ME group (P < 0.05). In conclusion, reducing dietary protein with balanced amino acids during the grower period and subsequent feeding with a low-energy diet promoted productive performance, improved protein utilisation and reduced fat accumulation via increasing lipolysis and/or disruption of the triglyceride transportation in broiler chickens.