The role of β-hydroxybutyric acid (BHBA) includes providing energy, regulating signaling pathways, and ameliorating the gut microbiota in the host, while its nutrient mechanism to improve rumen epithelium development in young ruminants is still unclear.  In this study, a total of 12 female Haimen goats with 30 d of age were chosen and divided into two groups.  One group was fed with basic diet (CON), and the other group was fed a basal diet supplemented with 6 g d–1 dietary β-hydroxybutyrate sodium (BHBA-Na).  The experimental period was 30 d, and all goats were slaughtered at 60 d of age.  The joint analysis of multi-omics, including rumen microbiota, rumen epithelial transcriptome and rumen epithelial metabolomics in young goat model, was performed to systematically investigate the effect of dietary BHBA-Na on rumen development in young goats.  As the results, we found that dietary BHBA-Na improved the growth performance of young goat including body weight, average daily gain (ADG) and dry matter intake (DMI) (P<0.05).  Dietary BHBA-Na also increased the weight of rumen, and promoted the growth of rumen epithelium development (P<0.05).  The abundance of several beneficial bacteria was increased (Fibrobacter, Succinivibrio, Clostridiales, etc.).  The rumen epithelium transcriptome and metabolomics indicated that BHBA-Na supplementation showed a remarkable effect on the nutrient metabolism of the rumen epithelium.  Specifically, the pathways of “fatty acid metabolism”, “cholesterol homeostasis”, “reactive oxygen species (ROS) pathway” and “peroxisome” were activated in response to BHBA-Na addition (P<0.05).  Moreover, the genes (HMGCS2, ECSH1, ACAA2, ECH1, ACADS etc.) and metabolites (succinic acid, alpha-ketoisovaleric acid, etc.) involved in these pathways were also regulated positively (P<0.05).  The rumen epithelium obtained the energy for its development from the process of volatile fatty acids (VFAs) decomposition.  Finally, we observed the close correlations among the phenotypes, ruminal microbiota, host genes and epithelial metabolites.  Overall, our results revealed that the BHBA-Na promoted the growth and rumen development of young goats possibly by enhancing DMI and regulating the rumen microbiota and the metabolisms of VFA and amino acid in the rumen epithelium.

The aim of this study was to investigate the effects of dietary fat on energy and nitrogen (N) metabolism efficiency, rumen fermentation, and microbiota in twin suckling lambs.  Thirty pairs of twin male lambs were randomly divided into two groups with one group receiving a high-fat diet (HF) and the other a normal-fat diet (NF).  Two diets (milk replacer and starter) of equal protein and different fat levels.  The metabolism test was conducted when the lambs were 50–60 days old, and nine pairs of twin lambs were randomly selected for slaughter to collect rumen fluid at 60 days old.  The result showed that fat addition increased the final body weight (BW), ruminal ammonia nitrogen (NH₃-N) content, proportion of propionic acid, and estimated methane production (CH_4e) (P<0.05).  The high fat diet tended to improve digestive energy (DE), metabolism energy (ME), DE/ME, utilisation of N (0.05<P<0.1).  However, microbial crude protein (MCP) content, total volatile fatty acids (VFA), acetic acid ratio, and the ratio of acetate to propionate (A:P) were lower than that in the NF group (P<0.05).  Regardless of whether fat is added or not, no different were observed in blood metabolites between the treatment.  High-throughput sequencing revealed that fat addition before weaning increased phyla Proteobacteria and genera of Succinivibrio, but decreased the relative abundance of Clostridium IV, Dialister, Roseburia, Acidaminococcus, and Megasphaera genera.  These findings indicated that high fat diet improved body weight, energy and nitrogen utilization may by shifting the rumen toward propionate fermentation via the enrichment of Succinivibrio.