This study aimed to evaluate the effects of aspirin eugenol ester (AEE) on growth performance, oxidative liver damage, inflammation, and liver metabolomics in broilers under high-stocking-density (HSD) stress. A total of 360 broilers were divided into four groups: normal density (ND, 14/m²), high density (HD, 22/m²), ND-AEE (ND + 0.01% AEE), and HD-AEE (HD + 0.01% AEE). HSD decreased total antioxidant capacity, increased malondialdehyde (MDA) levels, and elevated the expression of cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase-1 (mPGES-1) mRNA, which contributed to the reduced performance of broilers. Specifically, HSD caused abnormalities in linoleic acid metabolism, leading to elevated levels of Prostaglandin E2 (PGE2) and Leukotriene B4 (LTB4) synthesis, which aggravated inflammation, increased liver lipid levels, and impaired ATP production. AEE counteracted the decline in broiler production performance induced by HSD by enhancing total antioxidant capacity, reducing MDA levels, protecting the liver from oxidative damage, and maintaining mitochondrial oxidative phosphorylation. AEE positively regulated the linoleic acid metabolism by promoting the synthesis of γ-linolenic acid and phosphatidylcholine, which reduced the synthesis of COX-2 and mPGES-1. AEE alleviated the metabolic imbalance caused by HSD stress and enhanced the efficiency of mitochondrial fatty acid oxidation, which reduced excess lipid accumulation in the liver and promoted ATP production. In summary, this study provides strong support for the dietary addition of AEE to alleviate liver oxidative damage, inflammation, and energy metabolism disorders caused by HSD stress.

Heat stress, high stocking density, and feed safety risks are common features of modern intensive poultry production and collectively disrupt metabolic homeostasis in chickens. These stressors promote oxidative stress, lipid metabolic dysfunction, and inflammatory activation, ultimately reducing growth performance and overall health. This review summarizes current evidence on the effects of major stressors under intensive farming conditions on lipid metabolic homeostasis, redox balance, and immune regulatory networks, with particular emphasis on the supplementation strategies and physiological effects of chlorogenic acid (CGA) in chickens. Available studies indicate that CGA may regulate lipid metabolic homeostasis through adenosine monophosphate-activated protein kinase (AMPK)-related signaling pathways, enhance antioxidant defenses mediated by nuclear factor erythroid 2 related factor 2 (Nrf2), and suppress inflammatory responses associated with nuclear factor κB (NF-κB), thereby contributing to protective regulation at multiple levels.

High-stocking-density (HD) environments can trigger systemic inflammatory responses, consequently impairing broiler growth. Given the broad anti-inflammatory properties of aspirin eugenol ester (AEE), this study investigated the effects of AEE supplementation on growth performance, immune organ indices, serum immunoglobulin levels, and hypothalamic inflammation-related markers in HD broilers. A total of 528 one-day-old male Arbor Acres (AA) broilers were randomly assigned to four groups: ND, HD, ND-AEE, and HD-AEE (ND, 14 birds/m²; HD, 22 birds/m²), with six replicate cages per treatment group over a 42-day experimental period. The results revealed that AEE significantly improved the growth performance of HD broilers. Immune organ indices, serum immunoglobulin levels, and the expression of spleen inflammatory factors was associated with the organismal inflammatory response, which manifested primarily during the late growth phase. On Day 35, AEE significantly suppressed (p < 0.05) the relative mRNA expression of p21-activated kinase 1 (PAK1) in the hypothalamus of HD broilers. On Day 42, AEE significantly reduced the relative mRNA expression of PAK1, p38 mitogen-activated protein kinase (p38MAPK), cyclooxygenase-2 (COX-2), prostaglandin E synthase 1 (mPGES-1), and interleukin-1β (IL-1β) (p < 0.05), while significantly elevating the relative mRNA expression of growth hormone-releasing hormone (GHRH) (p < 0.05). Collectively, these findings demonstrate that AEE mitigates high-density rearing-induced hypothalamic inflammation and is associated with downregulated mRNA expression of PAK1 and its downstream targets in the p38MAPK/COX-2 axis. This gene expression profile correlates with improved growth and immune function in high-density-stressed broilers, suggesting a potential regulatory link that requires further validation at the protein and functional levels.