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 (R) 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 14-21. 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.