Simple SummaryIn this study, multi-omics techniques were used to reveal the effects of actual temperature and humidity index (THI) on intestinal microbe, function and serum metabolism of Ira rabbits. The increase of THI had a significant effect on the intestinal microbial structure of meat rabbits. In response to environmental THI changes, intestinal microorganisms with similar functions were replaced with each other, harmful bacteria were increased, heat-sensitive factors were upregulated, and disease-related biomarkers were increased in serum. In addition, the potential biomarkers of serum metabolism could be predicted with high predictive accuracy. In future production, the rapid detection of biomarkers, which has guiding significance for scientific meat rabbit production, can be attempted to determine whether the use of THI in the small environments of meat rabbits is suitable.AbstractThis study investigates the effects of different THI values on growth performance, intestinal microbes, and serum metabolism in meat rabbits. The results showed that there were significant differences in THI in different location regions of the rabbit house. The high-THI group (HG) could significantly reduce average daily gain and average daily feed intake in Ira rabbits (p< 0.05). The low-THI group (LG) significantly increased the relative abundance ofBlautia(p< 0.05). The HG significantly increased the relative abundance ofLachnospiraceae NK4A136 groupand reduced bacterial community interaction (p< 0.05). The cytokine–cytokine receptor interactions, nuclear factor kappa B signaling pathway, and toll-like receptor signaling pathway in each rabbit’s gut were activated when the THI was 26.14 (p< 0.05). Metabolic pathways such as the phenylalanine, tyrosine, and tryptophan biosynthesis and phenylalanine metabolisms were activated when the THI was 27.25 (p< 0.05). Meanwhile, the TRPV3 and NGF genes that were associated with heat sensitivity were significantly upregulated (p< 0.05). In addition, five metabolites were found to be able to predict THI levels in the environment with an accuracy of 91.7%. In summary, a THI of 26.14 is more suitable for the growth of meat rabbits than a THI of 27.25, providing a reference for the efficient feeding of meat rabbits.