Dietary Fat Sources Affect Hepatic Health, Performance and Gut Microbiota Composition in Laying Hens as Model

Non-alcoholic fatty liver disease (NAFLD) is a growing concern in both human and animal health, with nutritional strategies playing a key role in its management. This study used a laying hen model to evaluate the effects of two high-fat diets, one containing margarine (MAR) and the other natural milk cream (NC) on hepatic health, egg production and gut microbiota composition. Both diets were formulated with 8% fat but differed in fatty acid profiles: MAR was rich in lauric and stearic acids, whereas NC contained more palmitic and oleic acids. Compared to NC, MAR-fed hens showed significantly higher total cholesterol, low-density lipoprotein cholesterol (LDL-cholesterol), liver fat, relative liver weight, abdominal fat and serum markers of liver damage (aspartate aminotransferase [AST], alkaline phosphatase [ALP], gamma-glutamyl transferase [GGT] and adiponectin) (p < 0.05). Microbiota analysis revealed that although Firmicutes and Bacteroidetes dominated in both groups, MAR-fed hens had lower microbial diversity (Shannon index) and altered relative abundance of Verrucomicrobia, Peptostreptococcaceae and Turicibacter (p < 0.05), indicating microbial dysbiosis. These findings demonstrate that the type of dietary fat-independent of total fat content-strongly influences liver function and gut microbial balance in poultry. The novelty of this study lies in showing how different fat sources, despite equal inclusion levels, can distinctly modulate the gut-liver axis. This provides practical feed formulation insights and advances understanding of the gut-liver axis in animal health.