Effect of dietary protein concentrations, amino acids and conjugated linoleic acid supplementations on productive performance and lipid metabolism of broiler chicks

The study investigated the effect of low-crude protein (CP), essential aminoacids (EAAs) and conjugated linoleic acid (CLA) on broiler growth performance. From 1 to 6 days of age, 196 male broiler chicks fed the same basal diet containing 22.5% of crude protein. From 7-28 days the chicks were assigned to 7 treatments (4 replicates, 7 birds/replicate). The control group fed a 21.5% CP diet, supplemented with DL-methionine (Met) and L-lysine (Lys). The low-CP diet (19% CP) was supplemented with Met+Lys (2EAAs group) or with Met, Lys, L-arginine, L-tryptophan and L-threonine (5EAAs group); 2EAAs and 5EAAs groups were also supplemented with 0, 2 or 4% CLA. The body weight gain (BWG) was the biggest (p<.01) in the control group; 2EAAs and 2EAAs 4% CLA groups had lower BWG than the three groups fed 5EAAs diets. Diet 5EAAs +2% CLA induced lower (p<.01) feed conversion ratio (FCR) than 5EAAs +4% CLA and also showed the lowest (p<.01) protein intake. Reducing CP in broiler diet increased (p<.01) the digestibility of CP. The total protein content of plasma was greater (p<.01) in 2EAAs _4% CLA and 5EAAs +4% CLA than in the control. Decreasing the protein content of the diet from 21.5 to 19.0% penalised the growth performance of broilers from 7 to 28 days of age and the administration of CLA at 2 or 4% was not able to support growth. However, addition of 5EAAs without or with 2 or 4% of CLA resulted in recovery of FCR and PCR.