Cecal bacterial community and metabolism in response to carnosic acid supplementation are associated with improved egg quality in late-laying hens

The application of carnosic acid, as the major polyphenol of rosemary extract, on the quality of eggs at late stage of production has not been well known. Our study detected the effects of carnosic acid on the quality of eggs in laying hens during the late stage, intestinal immune and barrier, and gut microbiota and metabolism. One hundred and sixty-eight “Jing Tint 6” laying hens (65-wk-old) were allocated to three diets without (CON) or with 50 mg/kg carnosic acid (LCA) and 100 mg/kg carnosic acid (HCA). This experiment lasted eight weeks and all birds were raised in wire-floored cages. High carnosic acid supplementation increased Haugh unit, enhanced superoxide dismutase (SOD) activity in serum and increased intestinal villus height and Claudin-1 mRNA abundance, as well as decreased yolk n-6/n-3 ratio, reduced serum levels of interleukin-6 (IL-6) and total cholesterol (TC) and down-regulated small intestinal IL-6 mRNA abundance ( P < 0.05). High carnosic acid could substantially alter the composition of cecal SCFA, especially increased cecal butyrate content ( P < 0.05). Importantly, butyrate concentration in the cecal content was significantly positively related to Haugh unit and serum SOD concentration ( P < 0.05) and negatively related to serum TC and IL-6 levels, and yolk n-6/n-3. The community and metabolic function of the cecal microbiota in the high carnosic acid group were markedly changed, which also supported the alternation in the cecal SCFA composition ( P < 0.05). Furthermore, our study found that high carnosic acid increased the abundances of glutaconyl-CoA decarboxylase and 3-oxoacid CoA-transferase ( P < 0.05). Overall, high carnosic acid increased egg quality by partially alleviating systemic inflammatory response, improving intestinal immunity and barrier, and regulating cecal microbiota and metabolism, suggesting that carnosic acid could be used as a potential supplement to enhance the production level in laying hens and the quality of eggs at late stage of production.