This study investigated the potential mechanisms by which oral supplementation of N-carbamylglutamate (NCG), an analogue of endogenous N-acetylglutamate (an activator of arginine synthesis) increases growth rate in sow-reared piglets. Two piglets of equal body weight (BW) and of the same gender from each lactating sow were allotted to receive oral administration of 0 (control) or 50 mg of NCG/kg BW every 12 h for 7 d. Piglets (n = 32; BW = 3 kg) were studied in the food-deprived or fed state following the 7 d of treatment. Overnight food-deprived piglets were given NCG or water (control) at time 0 and 60 min. Piglets studied in the fed state were gavage-fed sow's milk with their respective NCG treatment at 0 and 60 min. At 60 min, the piglets were administered a flooding dose of [3H]phenylalanine and killed at 90 min to measure tissue protein synthesis. Piglets treated with NCG gained 28% more weight than control pigs (P < 0.001) over the 7-d period. Fed pigs had greater rates of protein synthesis in longissimus dorsi and gastrocnemius muscles and duodenum compared with food-deprived pigs (P < 0.001). Absolute protein synthesis rates in longissimus dorsi (P = 0.050) and gastrocnemius (P = 0.068) muscles were 30 and 21% greater, respectively, in NCG-treated compared with control pigs. Piglets supplemented with NCG also had greater plasma concentrations of arginine and somatotropin than control pigs (P < 0.001). The results suggest that oral NCG supplementation increases plasma arginine and somatotropin levels, leading to an increase in growth rate and muscle protein synthesis in nursing piglets. J. Nutr. 137: 315-319, 2007.