Effects of dietary concentration of threonine on growth performance, meat quality, antioxidant capacity, stress biomarker, and intestinal barrier function in broiler chickens raised under multiple stress conditions

Abstract

The objective of the present study was to investigate the effects of multiple stress conditions and dietary concentrations of threonine (Thr) on growth performance, meat quality, antioxidant capacity, stress biomarkers, and intestinal barrier function in broiler chickens. A total of 2052 21-d-old broiler chickens were randomly allotted to 6 treatments with 6 replicates per treatment in 2 × 3 factorial arrangements. Main factors included rearing environment and dietary concentrations of Thr. Birds were separately reared under normal or MS conditions of both heat stress and high stocking density. The basal diet was formulated to meet the recommended Thr concentrations (6.8 g/kg) of growing broiler chickens, and additional 2 diets were prepared by increasing concentrations of digestible Thr by 1.5-fold (10.2 g/kg) and 2-fold (13.6 g/kg) higher than Thr concentrations in the basal diet. Birds were reared at normal conditions (thermoneutral conditions and 9 birds/m²) or stressful conditions (cyclic heat stress and 18 birds/m²). Results indicated that no interactive effects of environmental conditions and dietary concentrations of Thr were observed in all measurements. However, birds raised under multiple stress conditions decreased (P < 0.05) growth performance, impaired (P < 0.05) immune response, disrupted (P < 0.05) intestinal morphology, and reduced (P < 0.05) tight junction related gene expression and had greater (P < 0.05) stress indicators, malondialdehyde concentrations, and intestinal permeability. In conclusion, broiler chickens raised under multiple stress conditions decreased immune response, intestinal morphology, and tight junction and increase stress response, antioxidant capacity, and intestinal permeability. Consequently, these factors collectively lead to reduction in growth performance. Furthermore, it can be concluded that dietary concentrations of Thr at 13.6 g/kg improves growth performance and intestinal health in broiler chickens, regardless of stress conditions.