Effects of High Ambient Temperature on Small Intestinal Morphology and Colonic Microbiota in Weaned Piglets.

A total of 16 crossbred (Duroc × Landrace × Yorkshire) barrows, with an average initial body weight of 8.61 ± 0.24 kg (28 days of age), were randomly allotted into the control group (CON group) and high ambient temperature group (HT group) with 8 replicates per group, 1 pig per replicate. The ambient temperature of the CON group was controlled at 26 ± 1 °C, and the HT group was controlled at 35 ± 1 °C. The study lasted for 21 days. Our results showed that high ambient temperature significantly decreased the average daily feed intake (ADFI) and average daily gain (ADG) of piglets ( p < 0.05), and the feed-to-gain ratio was significantly increased ( p < 0.05). The liver index, spleen index, and thymus index of piglets in the HT group were significantly decreased ( p < 0.05). The villous height (VH) of the duodenum, jejunum, and ileum of piglets in the HT group was significantly decreased ( p < 0.05), whereas the crypt depth (CD) of the duodenum was significantly increased ( p < 0.05), and the VH-to-CD ratio of the duodenum and ileum was significantly decreased ( p < 0.05). The piglets in the HT group showed a higher ( p < 0.05) observed-species index, PD whole tree index, and Shannon index, indicating that there was a significant difference in species richness and diversity between the two groups. At the genus level, the piglets in the HT group showed a greater ( p < 0.05) percent of Desulfovibrio , Occillibater , and Catenisphaera . HT reduced glycan biosynthesis and metabolism, transport and catabolism, lipid metabolism, amino acids metabolism, secondary metabolites biosynthesis, aging, endocrine system, signaling molecules, and interaction of colon microbiota ( p < 0.05), and increased signal transduction, cell motility, transcription, and genetic information processing ( p < 0.05).