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.

Broilers grown in a high-density (HD) stocking environment may experience intense competition that may adversely affect their growth relative to animals reared at a normal density (ND). The growth performance of HD broilers is increased by aspirin eugenol ester (AEE), although the mechanism by which this compound modulates hypothalamus-regulated feeding behavior is unclear. The aims of this study were to determine the effects of including AEE in the basal diet on the hypothalamic transcriptome and to examine in parallel the impact of these modifications on broiler production performance in HD conditions. Three hundred sixty one-day-old male Arbor Acres broilers were randomly divided into four groups: an ND group (14 broilers/m²), HD group (22 broilers/m²), ND-AEE group, and HD-AEE group. Each treatment group had 10 replicates, with 7 broilers per replicate in the ND and ND-AEE groups and 11 broilers per replicate in the HD and HD-AEE groups. Broiler growth performance was monitored, and hypothalamus samples were collected for transcriptome analysis on day 28. The HD group exhibited a reduced body weight (p < 0.01) at this timepoint compared to the ND group. However, the addition of AEE significantly improved average daily feed intake, average daily gain, and feed conversion ratio in the HD group from days 22 to 28 compared to the HD group without AEE (p < 0.05). The transcriptome results showed that 20 signaling pathways were commonly enriched among the groups (ND vs. HD, HD vs. HD-AEE). Several potential candidate genes were identified as involved in chicken central nervous system development and regulation of feed intake. Thus, the current study provides new insights into hypothalamic transcription patterns that are associated with the ameliorative effects of AEE in HD broilers.

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.