Effects of dietary glutamine and gamma-aminobutyric acid on performance, carcass characteristics and serum parameters in broilers under circular heat stress

This experiment was conducted on broilers to evaluate the effects of dietary glutamine (Gln, 0 and 5 g/kg) and gamma-aminobutyric acid (GABA, 0 and 100 mg/kg) on growth performance, carcass characteristics and serum parameters in broilers under circular heat stress (HS). A total of 360 21-day-old Arbor Acre male chicks were randomly assigned to five treatment groups (6 replicates of 12 birds per cage). The positive control (PC) broilers were kept in a thermoneutral chamber (average 23 °C) and fed with a basal diet. The other four groups were kept in a circular HS chamber (30–34 °C) for 9 h (from 09:00 to 18:00). The experiment lasted from 22 to 42 day posthatch. Circular HS decreased (P<0.001 or 0.05) body weight (BW), weight gain (WG), feed consumption (FC), eviscerated weight (EW), breast muscle weight (BMW), breast muscle yield (BMY), thigh muscle weight (TMW), abdominal fat weight (AFW), abdominal fat yield (AFY), serum concentrations of T3, T4, insulin, Gln and glutamate (Glu), while increased feed-to-gain ratio (FGR), thigh muscle yield (TMY), serum concentrations of nitric oxide synthase (NOS) activity and corticosterone (CS) compared to the PC group. The diet supplemented with 5 g/kg Gln increased (P<0.001 or 0.05) BW, WG, FC, EW, BMW, BMY, TMW, AFW, AFY, serum concentrations of insulin and Gln, while decreased FGR, NOS activity and CS concentration. The addition of 100 mg/kg GABA increased (P<0.001 or 0.05) WG, FC, EW, BMW, BMY, AFW, AFY, serum concentrations of T3, insulin, Gln, GABA and Glu, while decreased CS concentration (P<0.05). Interactions were found between Gln and GABA for FGR (P=0.044), EW (P=0.042), eviscerated yield (P<0.001), BMW (P=0.002), BMY (P<0.001), TMY (P=0.001), AFW (P<0.001), AFY (P<0.001), serum concentrations of T3 (P<0.001), T4 (P<0.001), insulin (P=0.003), GABA (P=0.034) and Glu (P<0.001) in broilers under circular HS. These results demonstrated that dietary Gln and GABA offered a potential nutritional strategy to prevent HS-related depression in performance and carcass characteristics of broiler.