Carnosic Acid from Rosemary Boosts Egg Quality in Late-Laying Hens by Reshaping Cecal Microbes

Supplementing the diets of older laying hens with carnosic acid, the major polyphenol in rosemary extract, improved several measures of egg quality and was associated with marked changes in the cecal bacterial community and its metabolism, according to a study published in Animal Microbiome. The work, released as a peer-reviewed accepted manuscript that is still subject to final editorial edits, suggests a possible nutritional route to sustaining egg quality late in the production cycle.

The researchers, led by Lianhua Zhang and Hongfu Zhang, allocated 168 “Jing Tint 6” laying hens, all 65 weeks old, to three dietary groups for eight weeks. One group received a basal diet without carnosic acid (CON), a second received 50 mg/kg carnosic acid (LCA), and a third received 100 mg/kg (HCA). All birds were housed in wire-floored cages. The study examined egg quality, serum biochemistry, intestinal immune and barrier markers, and the composition and metabolic function of the cecal microbiota.

In the high-dose group, several outcomes moved in a favorable direction. Haugh unit, a standard measure of egg albumen quality, increased, as did superoxide dismutase (SOD) activity in serum, an indicator of antioxidant capacity. Intestinal villus height and the mRNA abundance of the tight-junction protein Claudin-1 also rose, while the ratio of n-6 to n-3 fatty acids in the yolk fell. All of these differences were statistically significant at P < 0.05.

The high-dose supplement was also linked to lower levels of inflammatory and metabolic markers in blood. Serum concentrations of interleukin-6 (IL-6), a pro-inflammatory cytokine, and total cholesterol (TC) decreased, and IL-6 mRNA abundance in the small intestine was down-regulated, again with P < 0.05. The authors interpret this pattern as a partial alleviation of systemic inflammatory response alongside improved intestinal immunity and barrier function.

A central finding concerned short-chain fatty acids (SCFA) in the cecum. High carnosic acid supplementation substantially altered the composition of cecal SCFA, most notably increasing cecal butyrate content.

Those cecal butyrate concentrations correlated with the host outcomes reported in the study. Butyrate in cecal contents was significantly positively related to Haugh unit and to serum SOD concentration, and negatively related to serum TC and IL-6 levels and to the yolk n-6/n-3 ratio (P < 0.05).

The community and metabolic function of the cecal microbiota in the high-dose group were markedly changed, changes that the authors say support the observed shifts in cecal SCFA composition (P < 0.05). In particular, high carnosic acid increased the abundances of two microbial enzymes: glutaconyl-CoA decarboxylase and 3-oxoacid CoA-transferase (P < 0.05).

The study’s scope and limitations are worth noting. The trial involved a single breed of hen at a single age, one eight-week feeding period, and cage housing, so the findings apply to late-stage production under these conditions rather than to laying hens generally. The reported associations between cecal butyrate and host measures do not establish causal mechanisms, and the microbiome results reflect the cecal compartment rather than the whole gastrointestinal tract. The authors conclude that carnosic acid could serve as a potential supplement to enhance production level in laying hens and egg quality at the late stage of production, positioning it as a candidate additive for further evaluation in poultry nutrition. Because the article is being shared early as an accepted manuscript, some details may be refined in the final version of record.

Subject of Research: Effects of dietary carnosic acid on egg quality, gut barrier and cecal microbiota in late-laying hens

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

Article References: Zhang, L., Lu, J., Piao, X., Chen, L., & Zhang, H. (2026). Cecal bacterial community and metabolism in response to carnosic acid supplementation are associated with improved egg quality in late-laying hens. Animal Microbiome. https://doi.org/10.1186/s42523-026-00638-6

Image Credits: AI Generated

DOI: 10.1186/s42523-026-00638-6

Keywords: carnosic acid, laying hens, egg quality, cecal microbiota, butyrate, rosemary extract, gut barrier, Haugh unit, short-chain fatty acids, poultry nutrition, Cecal, bacterial