This study investigated the interactive effects of lysine restriction, crude protein (CP) reduction and vitamin fortification ± insoluble fibre (Arbocel®) – on skeletal integrity, locomotion and behaviour of broilers. A 2 × 2 × 2 + 1 factorial design tested nine diets in 756 male Ross308 broilers from d10 to 40. The factors included lysine (6.2% and 5.7% of dLys/CP), two vitamin levels (standard and high), and fibre (0 or 5 g/kg) + Ross-based control. A 12% CP reduction numerically increased the tibial fracture force (≈13.1 N) (P > 0.05). Insoluble fibres increased the bone ash weight (P < 0.05), while lysine and vitamin showed no main effects. The control had the lowest level of bone phosphorus (P < 0.05). The apparent bone density was influenced by interactions, declining with decreasing lysine and vitamin contents but improving in high-vitamin diets without fibre. Significant Lysine × Fibre and Vitamin × Fibre interactions affected bone density and DBL/SHK.L, while lysine influenced DBL/SHK.L. Locomotor outcomes: gait improved with high vitamin/fibre intake, and lysine restriction reduced severe lameness (Gait score of 5) and influenced weight-adjusted gait (P = 0.007). Foot pad condition excellent (≥98.8% FPLS0). The bone phosphorus content was strongly negatively predicted by dietary CP and lysine intake (R² = 0.507, p < 0.001). Findings guide the formulation of low-protein diets that maintain broiler welfare.
Salahi et al. (Fri,) studied this question.