Effect of dietary non-essential amino acid sources on performance, nitrogen utilization and blood parameters for broiler chickens fed a low-protein diet

Two experiments were carried out to evaluate sources of non-essential amino acids (NEAA) in low-protein diets and their effects on performance, nitrogen retention, and blood parameters in broiler chickens. In the first experiment: three dietary treatments were formulated with 10 replicate pens and five male Cobb-500 broiler chickens per experimental unit: T1, positive control (PC) diet with 222.5 g/kg crude protein (CP) and an essential-to-total nitrogen ratio (eN-to-tN) of 0.4766; T2, negative control (NC) with 205 g/kg CP and an eN-to-tN of 0.5156; T3, 205 g/kg CP + 2.8 g/kg of glutamate (Glu), and an eN-to-tN of 0.5163. In the second experiment: six dietary treatments were fed to 10 replicate pens of five male Cobb-500® broiler chickens as follows: T1, PC with 222.5 g/kg CP and an eN-to-tN of 0.4706; T2, NC diet with 205 g/kg CP and an eN-to-tN of 0.5695; T3, NC + 3.846 g/kg glycine (Gly) and an eN-to-tN of 0.4706; T4, NC + 4.041 g/kg alanine (Ala) and an eN-to-tN of 0.4706; T5, NC + 7.287 g/kg Glu and an eN-to-tN of 0.4706; T6, NC + 4.080 g/kg NEAA mixture (Gly + Ala + Glu) and an eN-to-tN of 0.4706. Performance was measured after 21 days. Excreta were collected to calculate nitrogen utilization from day 14 to 21. Blood was collected to quantify uric acid, total protein, albumin and globulin and to evaluate nitrogen utilization. When crude protein was reduced from 222.5 to 205 g/kg CP, it resulted in a worsening of body weight gain (BWG) and feed conversion ratio (FCR). A low CP diet supplemented with glutamate increased BWG and decreased the FCR. The values of nitrogen intake (NI) and nitrogen balance (NB) were higher (P<0.05) in the PC and NC + Glu treatments than in the NC. In the second experiment, NC + Gly resulted in lower BWG and higher feed intake (FI), but the FCR was better than in the other treatments. Serum uric acid was highest in the NC + Glu, Ala and NEAA mixture. The NI was lowest in the NC + Gly treatment, whereas in this same treatment we observed the highest NB. A low CP diet supplemented with glutamate, alanine and NEAA and an eN:tN of 0.4706 improved the broilers' BWG, FCR, and nitrogen utilization efficiency more than a low CP diet with 205 g/kg CP and an eN:tN ratio of 0.5695.