Dietary supplementation of protocatechuic acid improves antioxidant capacity and intestinal health in late-laying hens

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A decline in the antioxidant capacity of the organism is observed in late-laying hens. Protocatechuic acid (PCA), a phenolic compound, possesses antioxidant and anti-inflammatory properties. However, whether dietary supplementation with PCA can alleviate these adverse effects in late-laying hens remains unclear. A total of 576 Hy-Line Brown laying hens aged 500 days were randomly divided into 4 groups, each with 6 replicates of 24 hens. The four groups consisted of a basal diet group (CK) and three experimental groups supplemented with 0.05, 0.1, and 0.2% PCA (LPCA, MPCA, and HPCA, respectively). The trial lasted 49 days, including a 1-week adaptation period followed by a 6-week experimental period. Dietary PCA supplementation significantly increased the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) and decreased the level of malondialdehyde (MDA). Furthermore, PCA supplementation also significantly decreased the levels of inflammatory factors such as tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6). Ileum transcriptomic analyses revealed that the differentially expressed genes were significantly enriched in pathways such as transmembrane transport activity, signal receptor binding, the PPAR signaling pathway, and intestinal immunity. We further sequenced cecal microbiota, showing that the structure of the microbiota has undergone significant changes; beneficial bacterial communities such as g_Bacteroides and g_Odoribacter were significantly enriched in the PCA treatment group. Metabolomic analysis revealed that the differential metabolites were predominantly enriched in pathways closely associated with intestinal digestive and absorptive functions, including tryptophan metabolism, arginine biosynthesis, cysteine and methionine metabolism, and glycerophospholipid metabolism, all of which were found to be activated. Subsequently, non-targeted metabolomic analysis revealed that these differential metabolites were primarily involved in tryptophan metabolism, arginine biosynthesis, cysteine and methionine metabolism, and glycerophospholipid metabolism. Therefore, supplementing PCA in the feed of late-laying hens can improve antioxidant capacity, inflammatory response, and intestinal microbiota composition to enhance intestinal health.