To evaluate the impact of different roughages on the intestinal microbiota of yak calves, we fed them oat hay in substitution of alfalfa hay, in addition to milk replacer and starter powder. Twenty-one 45-day-old male yak calves were selected and randomly assigned to three groups: the milk replacer + starter + alfalfa hay group (AH), the milk replacer + starter + oat hay group (OH), and the milk replacer + starter + mixed hay group (AO), in which the alfalfa hay and oat hay were administered in a 1:1 ratio. All calves in the three groups were fed the same milk replacer and an equivalent amount of dry matter. The formal experiment commenced after a 21-day pre-test period and lasted for 120 days. Following the experiment, the contents of the jejunum and colon were collected to investigate the intestinal microbiota and metabolites using 16S rRNA sequencing and LC-MS metabolomics. The result showed that the AO group had greater final body weights overall than the AH group and OH group (p < 0.05). The AH group and OH group had considerably greater feed-to-gain ratios than the AO group (p < 0.05). At the phylum level, the OH group exhibited an increased relative abundance of Bacteroidota and Spirochaetota in the jejunum (p < 0.05). The relative abundance of Actinobacteriota in the colon was increased in the AO group (p < 0.05). At the genus level, the AO group exhibited a decreased abundance of Clostridium sensu_stricto_1 (p < 0.05), and the OH group showed an increased abundance UCG-005 and Alistipes in the jejunum. There were many differential metabolites in the OH group and AO group compared to the AH group, and the different metabolites of the OH group were associated with the metabolic pathways of the nervous system, sensory system, amino acid metabolism, and lipid metabolism in the jejunum and with lipid metabolism, amino acid metabolism, and the nervous system in the colon. In the AO group, these metabolites were associated with the digestive system and the translation and metabolism of cofactors in the jejunum and with the metabolism of cofactors and vitamins in the colon. In summary, it is feasible to replace alfalfa hay with oat hay based on milk replacer and starter. The combination of the two forages enhanced nutrient absorption, improved immune function, maintained the internal homeostasis of yak calves, and was more beneficial to their growth and development.

Early-life nutrient supply plays an important role in regulating growth and gastrointestinal development in young ruminants. However, the effects of restri

This study investigated the effects of starter feed supplementation on growth performance, immune-related parameters, intestinal microbiota, and metabolite profiles in preweaning yak calves. Twenty healthy 30-day-old male yak calves with similar body weight were randomly assigned to either a control group (A), receiving milk replacer and alfalfa hay, or a starter-supplemented group (AS), receiving milk replacer, alfalfa hay, and a concentrate-based starter feed. Growth traits, nutrient digestibility, serum immune indices, intestinal microbial communities, and metabolomic characteristics were evaluated. Compared with the A group, calves in the AS group exhibited greater total dry matter intake, final body weight, heart girth, cannon circumference, and apparent digestibility of calcium and phosphorus (p < 0.05). Average daily gain tended to increase but did not differ significantly between treatments (p > 0.05). Starter supplementation also increased serum concentrations of IgA, IL-6, TNF-α, M-CSF, and IFN-γ (p < 0.05). In contrast, jejunal TNF-α concentration was lower in the AS group than in the A group (p < 0.05). Microbial analysis demonstrated that starter supplementation modified intestinal bacterial community composition. In the jejunum, the relative abundances of Family_XIII_AD3011_group and Acetitomaculum were increased, whereas Bacteroidota and Bacteroides were enriched in the colon. Untargeted metabolomic analysis further revealed distinct metabolic profiles between groups, with differential metabolites mainly associated with amino acid metabolism, vitamin metabolism, and energy-related pathways. Overall, starter feed supplementation was associated with changes in nutrient utilization, immune-related indicators, intestinal microbial composition, and metabolic characteristics. These findings suggest that starter supplementation may facilitate dietary adaptation and support gastrointestinal function in preweaning yak calves.

The objective of this study was to investigate the effects of supplemental starter feeding on the development of the ruminal epithelium in suckling yak calves using transcriptomic analysis. Twenty healthy one-month-old male yak calves with similar body weights were selected and randomly assigned to two groups. The pre-feeding adaptation period lasted 14 days, followed by a 120-day experimental feeding period. At the end of the trial, five calves from each group were slaughtered, and samples of abomasum tissue and ruminal contents were collected for subsequent analyses. The results demonstrated that early concentrate supplementation markedly increased the final body weight and ruminal NH₃-N concentration of calves in the RAS group compared with the control (RA) group (p < 0.05). Similarly, dry matter intake and ruminal microbial protein (MCP) content were significantly higher in the RAS group (p < 0.05). In contrast, the concentration of acetic acid in ruminal fluid was significantly higher in the RA group, whereas valeric acid concentration was higher in the RAS group. Furthermore, ruminal TNF-α, TNF-γ, and IL-2 concentrations were significantly elevated in the RAS group (p < 0.05), suggesting enhanced ruminal immune function. Transcriptomic analysis revealed that both up- and down-regulated gene expression contributed to the morphological development and overall health of the ruminal epithelium. Up-regulated genes were enriched in pathways related to chemical carcinogenesis, cytochrome P450 metabolism, steroid hormone biosynthesis, retinol metabolism, ascorbate and aldarate metabolism, drug metabolism-cytochrome P450, pentose and glucuronate interconversions, ovarian steroidogenesis, and porphyrin and chlorophyll metabolism. Conversely, down-regulated genes were mainly associated with cytokine–cytokine receptor interactions, mineral absorption, arachidonic acid metabolism, and viral protein interactions with cytokine receptors. Overall, early supplementation with concentrate feed enhanced the expression of genes associated with ruminal epithelial development, improved immune responses, and promoted better growth performance in suckling yak calves.

To investigate the intestinal development process of yak calves at different ages. Twenty-one healthy male yak calves from the same birth cohort, aged 60&#

Early-life dietary intervention plays an important role in rumen development and is associated with changes in ruminal microbial communities and metabolic