Arginine amino acid, nano particles of zinc oxide, and stock density: Effect on growth performance, intestinal morphology, blood indices, and meat quality in broiler chickens

The objective of this study was to investigate the effects of Nano Zinc Oxide (NZnO) supplements and arginine (Arg) on the growth performance, intestinal morphology, blood indices, and meat quality of Arian broiler chickens under high stocking density (HSD) conditions. A total of 672 one-day-old broiler chickens were assigned in a completely randomized design with a 2 × 2 × 2 factorial arrangement, included two levels of arginine (100 and 130 % of the Arian recommendation), two levels of nano zinc oxide (0 and 50 mg/kg), and two stocking densities (12 and 16 birds/m²), resulting in eight treatments with six replications. Results, revealed that HSD resulted in decreased daily body weight gain (DBWG) (P < 0.001), and daily feed intake (DFI) (P = 0.008) throughout the rearing period. However; the inclusion of NZnO or Arg (130 %) improved DBWG over the entire period (P < 0.05). NZnO supplementation increased DFI during finisher 2 (P = 0.001) and the entire period (P = 0.009). Interaction effects between stocking density, NZnO, and arginine demonstrated that chickens raised in HSD and fed diets without NZnO and arginine exhibited the lowest weight gain during finisher 2 (P = 0.006) and the highest FCR for both finisher 2 (P = 0.001) and the entire period (P = 0.047). Moreover; HSD led to reduced carcass, breast, and thigh weights, whereas NZnO and arginine improved breast weight (P < 0.05). The NZnO supplementation decreased heart weight and increased spleen weight (P < 0.05). The villus height, width, and absorption area were negatively affected by HSD (P < 0.05), whereas NZnO supplementation increased these traits as a main effect (P < 0.05). The HSD increased glucose concentration, whereas 130 % arginine increased albumin concentration and GPx activity and decreased ALT activity (P < 0.05). Additionally; NZnO increased Superoxide dismutase (SOD), GPx, and ALT enzyme activity compared to the control (P < 0.05). Furthermore; NZnO supplementation in HSD increased SOD enzyme activity (P < 0.05). Notably; the interaction effect of SD × Arg × NZnO indicated that chickens raised in HSD without any additives had the lowest total protein and highest triglyceride concentration (P < 0.05). Moreover, nitric oxide concentration in HSD was lower than in low stocking density (LSD), and increasing dietary arginine levels improved nitric oxide concentration and vessel diameter (P < 0.05). The HSD reduced water holding capacity and increased cooking loss (CL) and malondialdehyde (MDA-48 h) content in meat (P < 0.05). However, 130 % arginine improved the meat CL (P < 0.05), and NZnO supplementation decreased pH-15 min, CL, and MDA-48 h levels in meat (P < 0.05). Notably; NZnO in HSD decreased MDA-48 h concentration in meat (P < 0.05). Overall, no significant Arg × NZnO × HSD interaction was observed for meat quality or morphological traits; however, the three-way interaction significantly influenced DBWG (36-42 d) and FCR (36-42 and 1-42 d), with the combination of 130 % arginine and 50 mg/kg NZnO improving performance under high stocking density conditions.