Effects of rumen-protected glucose on ileal microbiota and genes involved in ileal epithelial metabolism and immune homeostasis in transition dairy cows.

• RPG supplementation attenuated local inflammation and promoted epithelial metabolism in the ileum. • RPG supplementation did not alter ileal microbiota in both digesta and mucosa. • RPG can serve as an effective dietary intervention to improve productive performance and health status of cows. Optimizing diet formula with the aim of alleviating negative energy balance (NEB) is of great significance to the production performance of transition dairy cows. The objective of the study was to evaluate the effects of rumen-protected glucose (RPG) supplementation on ileal microbiota, the expression of genes involved in epithelial metabolism and immune homeostasis in the ileum of transition dairy cows. Ten Holstein dairy cows (age, 4.7 ± 0.5 years; bodyweight, 515 ± 42 kg; parity, 2.8 ± 0.4; body condition score, 3.2 ± 0.3; milk yield, 16.1 ± 3.7 kg/d) were randomly divided into two groups. The treatments were a basal diet plus 200 g/d of RPG (450 g/kg of glucose, 450 g/kg of coating fat and 100 g/kg of water) or a basal diet plus 90 g/d of coating fat (CON). Cows were provided with the diets for 21 days (from 1 week prepartum to 2 weeks postpartum) and euthanized on d 22 for taking samples. The ileal digesta samples were taken from the mid-ileum to analyze volatile fatty acid concentration and composition of digesta-associated microbiota. The ileal mucosa samples were taken from the mid-ileum for analysis of gene expression and composition of mucosa-associated microbiota. Ileal total volatile fatty acid concentration was lower (P = 0.018) in the PRG-supplemented group than in the CON group. Compared with CON group, the PRG supplementation up-regulated or tended to up-regulate (P < 0.10) the expression of PC , SGLT3, IGFBP5, PPARA, IL10 , Occludin , and TPJ1 , but down-regulated the expression of IL17A (P = 0.032) and tended to down-regulate (P < 0.10) the expression of TLR4 , TLR9 and IL26. However, no differences (P > 0.10) were observed between the RPG and CON groups in both ileal total bacterial copy number and ileal bacterial beta diversity. Collectively, dietary RPG supplementation promoted epithelial metabolism and improved immune homeostasis in the ileum, with no influence on both digesta- and mucosa-associated ileal microbiota of transition dairy cows. [ABSTRACT FROM AUTHOR]