In-depth investigation of the mechanisms of high and low residual feed intake regulating hens during the late laying period via liver and gut microbiota.

Residual feed intake (RFI) is a more accurate indicator of feed efficiency than the feed conversion ratio (FCR) and is widely used to measure the efficiency of livestock and poultry feed utilization. Typically, Low RFI (LRFI) implies higher feed conversion efficiency, while high RFI (HRFI) indicates lower feed conversion efficiency. This study systematically explored the differences between high and low RFI and the function of the liver and cecum microbes of hens during the late laying period by multiple-omics techniques and further explored the interaction among microorganisms, the function of tissues and organs, and body metabolism. The results showed that the length and mass of the digestive organs in the LRFI group were higher than those in the HRFI group as well as the chest width. Additionally, the key genes and metabolites regulating RFI in hens during the late laying phase were found to be ADCY2, ADCY8, CCKAR, ACSS2, FABP1, FABP4, and LysoPI (18:2(9Z,12Z)/0:0) in the liver. The levels of AST, HDL-C and ACTH in the serum were considered candidate markers influencing RFI. By conducting a microbiome-metabolome association analysis, we have identified the dominant and beneficial microbial community in the gut of LRFI groups, such as Oscillospirales, Ruminococcaceae, and Butyricicoccaceae, which offers a theoretical basis for understanding how the gut microbiota regulates RFI. These results will provide a scientific basis for the molecular mechanism of RFI phenotypic variation in late laying hens.