Effects of dietary glucogenic amino acid supplementation on growth performance, body composition and plasma free amino acid levels in genetically lean and fat chickens

Two experiments were conducted to investigate the effects of pair-feeding, nutritional status (fasting vs feeding ad libitum) and supplementing diets with alanine (2 g/kg), threonine (2 g/kg), glutamic acid (5 g/kg) and arginine (5 g/kg) on growth performance, body composition and free plasma amino acid levels in genetically lean (LL) or fat (FL) chickens of 4 to 7 weeks of age. When fed ad libitum, FL chickens ate more than LL birds and showed higher lipid and protein gains. However, when pair-fed, FL birds exhibited increased lipid retention but lower protein gain. Growth performance and body composition were not significantly affected by the addition of glucogenic amino acids to the diets. However, amino acid supplementation slightly improved food to gain ratios but depressed gross energy and protein efficiencies in both lines. FL chickens had lower plasma levels of most glucogenic amino acids and higher levels of branched-chain and sulphur amino acids than LL birds, irrespective of diet and nutritional status. These results are discussed in relation to hormonal characteristics of FL and LL birds.