Fecal Virome Transplantation Confirms Non-Bacterial Components (Virome and Metabolites) Participate in Fecal Microbiota Transplantation-Mediated Growth Performance Enhancement and Intestinal Development in Broilers with Spatial Heterogeneity.

Fecal microbiota transplantation (FMT) promotes growth performance and intestinal development in yellow-feathered broilers, but whether the virome and metabolites contribute to its growth-promoting effect remains unclear. This study removed the microbiota from FMT filtrate using a 0.45 μm filter membrane, retaining the virome and metabolites to perform fecal virome transplantation (FVT), aiming to investigate its regulatory role in broiler growth. Healthy yellow-feathered broilers with high body weights (top 10% of the population) were used as FVT donors. Ninety-six 8-day-old healthy male yellow-feathered broilers (95.67 ± 3.31 g) served as FVT recipients. Recipient chickens were randomly assigned to a control group and an FVT group. The control group was gavaged with 0.5 mL of normal saline daily, while the FVT group was gavaged with 0.5 mL of FVT solution daily. Growth performance, immune and antioxidant capacity, intestinal development and related gene expression, and microbial diversity were measured. The results showed that FVT improved the feed utilization rate of broilers (the feed conversion ratio decreased by 3%; < 0.05), significantly increased jejunal length (21%), villus height (69%), and crypt depth (84%) ( < 0.05), and regulated the jejunal barrier: insulin-like growth factor-1 () (2.5 times) and Mucin 2 () (63 times) were significantly upregulated ( < 0.05). FVT increased the abundance of beneficial bacteria . However, negative effects were also observed: Immunoglobulin A (IgA), Immunoglobulin G (IgG), Immunoglobulin M (IgM), Interleukin-1 beta (IL-1β), Interleukin-6 (IL-6), Tumor Necrosis Factor-alpha (TNF-α), and Interferon-gamma (IFN-γ) in broilers were significantly upregulated ( < 0.05), indicating immune system overactivation. Duodenal barrier-related genes Mucin 2 (), Occludin (), Claudin (), and metabolism-related genes solute carrier family 5 member 1 () and solute carrier family 7 member 9 () were significantly downregulated ( < 0.05). The results of this trial demonstrate that, besides the microbiota, the gut virome and metabolites are also functional components contributing to the growth-promoting effect of FMT. The differential responses in the duodenum and jejunum reveal spatial heterogeneity and dual effects of FVT on the intestine. The negative effects limit the application of FMT/FVT. Identifying the primary functional components of FMT/FVT to develop safe and targeted microbial preparations is one potential solution.