Embryonic thermal manipulation improved early cecal microbial diversity, metabolic pathways, and immunity in broiler chickens

Gut microbiota regulates broilers' gastrointestinal functions, digestion, metabolism, and immune responses. Modulating the microbiota in the early stage could present a promising approach for the poultry industry. Embryonic thermal manipulation (TM) constitutes a promising strategy for sustainable broiler production. Our previous research has yielded significant insights into the impact of TM on embryonic thermotolerance, metabolism, post-hatch growth performance, microbial diversity, and immunity. This follow-up study utilized a subset of birds from our previous study to investigate the effects of TM on early cecal microbiota composition, predicted metabolic pathways, and ileum immunity-related genes. A total of 600 fertile Cobb 500 eggs were incubated for 21 d. After candling, 238 eggs underwent TM at 38.5 °C with 55% relative humidity (RH) from embryonic day (ED) 12 to 18, then were transferred to a hatcher at 37.5 °C from ED 19 to 21, while 236 eggs were incubated at 37.5 °C throughout until 21 d. After hatching, 60-day-old unsexed chicks were housed in 12 pens (10 birds/pen, 6 replicates per treatment). The treatments included 1) Control and 2) TM. All birds were raised under standard conditions (22-24 °C) for the first 21 d. This study evaluated the effects of embryonic TM on four parameters: the composition of cecal microbiota (relative abundance at multiple taxonomic levels), microbial diversity indices (both alpha and beta diversity), predicted microbial metabolic pathways, and the expression of ileal immune-related genes on days 7, 14, and 21. TM significantly increased (P < 0.05) microbial beta diversity (Bray-Curtis, Jaccard and, unweighted UniFrac) and metabolic microbial pathways at days 7, 14, and 21. In the ileum, at d 7, the mRNA expression of IL10, IL12, IL18, TLR1, TLR2A, TLR4, TLR21, TBK1, TGFb, TGFb3, IFNg, NFkB, and CD3 was significantly lower (P < 0.05) in the TM group compared to the Control group. There was no significant difference (P < 0.05) between the treatment groups at d 14. However, at d 21, IL4, IL6, AvBD6, and IFNg were significantly lower (P < 0.05), and TLR2A and TGFb3 expression were significantly higher (P < 0.05) in the TM group compared to the Control group. Embryonic TM significantly increased cecal microbial diversity and predicted metabolic pathways, thereby improving ileum immunity in the early stages of life in broiler chickens.