Abstract
Background:
Low-protein diets are increasingly applied in broiler production to reduce nitrogen excretion and environmental impact; however, they may impair growth performance, antioxidant status, and intestinal health. Phytogenic feed additives, particularly polyherbal mixtures, have been proposed as natural strategies for mitigating these negative effects.

Aim:
This study aimed to investigate the effects of polyherbal mixtures on broiler growth performance, serum antioxidant markers, intestinal histomorphology, tight junction and cytokine gene expression, litter quality, and welfare indicators.

Methods:
A total of 600 one-day-old Cobb 500 chicks were assigned on day 11 to 2 dietary treatments with 10 replicates of 30 birds per pen. Treatments included a commercial normal-protein diet (CON) and a low-protein diet plus a polyherbal mixture at 2,600 mg/kg (LPD-HM).

Results:
During the grower phase (days 11–21), the LPD-HM increased feed intake but did not affect the final body weight (FBW) or body weight gain (BWG); the feed conversion ratio (FCR) was higher, and the index performance was lower than those fed the CON diet. In the finisher phase (days 22–35), the growth performance did not differ between the groups. Across days 11–35, the FBW and BWG were maintained, whereas the cumulative FCR was higher with the LPD-HM, indicating that the feed efficiency was not fully restored. LPD-HM improved the serum antioxidant status, with higher superoxide dismutase, glutathione peroxidase, and total antioxidant capacity and lower malondialdehyde levels. Intestinal histomorphology did not differ between the groups. The tight-junction gene occludin and the cytokine genes tumor necrosis factor-α, interleukin-10, and interleukin-13 were significantly upregulated with LPD-HM. Furthermore, litter pH and litter ammonia were lower with LPD-HM, whereas litter moisture and total nitrogen tended to decrease. In addition, footpad dermatitis scores decreased with the LPD-HM, whereas breast dermatitis, hock burn, and bird soiling scores remained unchanged.

Conclusion:
Dietary LPD-HM maintained FBW and BWG but did not fully restore feed efficiency while modulating antioxidant status, barrier-related gene expression, litter chemistry, and footpad health.

Key words: Antioxidant status; Broiler; Litter ammonia; Low-protein diet; Polyherbal mixture