Different Feeding Paradigms of Yak Calves During Pre-weaning Period Changed Rumen and Intestinal Development and Function by Altering Gastrointestinal Microbiota

Understanding the gastrointestinal microbiota of yak calves during pre-weaning periodis important to illuminate the effects of different feeding paradigms (maternal grazingand barn feeding groups) on the performance, gastrointestinal development, nutrientutilization, and immune function in yak calves.ResultsCompared with the yaks in maternal grazing group, the significantly increased bodyweight, body height, body length, chest girth, weight of liver, spleen, and thymus, aswell as organ index of thymus and pancreas were all identified in yaks of barn feedinggroup (P < 0.05). The total volatile fatty acid, propionate, butyrate, isobutyrate, andvalerate of rumen were significantly higher in the barn feeding group (P < 0.01). Therumen pectinase, the duodenal a-amylase, the jejunal a-amylase and trypsin, and theileal trypsin of yaks in barn feeding group were significantly increased (P < 0.05). Thelength and width of rumen nipple, the villus height and crypt depth of duodenum,jejunum, and ileum in barn feeding group were all significantly increased (P < 0.05).The RNA sequencing of rumen epithelial identified that most of altered genes wereinvolved in the enhanced immune functions of yaks in barn feeding group. By usingELISA, the duodenal IL-1ß, the jejunal IL-1ß, IL-2, TNF-a, and IFN-?, as well as ileal IL-1ß were significantly increased (P < 0.05) in the barn feeding group. By using 16SrDNA sequencing, some significantly increased genus in barn feeding group wereidentified, including the increased rumen genus of Sharpea, Sphingomonas,Atopobium, Syntrophococcus, Clostridium_XIVb, Acinetobacter, Oscillibacter, Dialister,Desulfovibrio, Bacteroides, Lachnospiracea_incertae_sedis, Methanosphaera,Methylobacterium and Clostridium_sensu_stricto, the increased jejunal genus ofodoribacter, lachnospira, syntrophococcus, propionibacterium, selenomonas, andkocuria, as well as the increased ileal genus of synergistes, atopobium,saccharibacteria_genera_incertae_sedis, syntrophococcus, selenomonas,succiniclasticum, anaerovibrio, sphingomonas, and lachnospiracea_incertae_sedi.ConclusionsThe barn feeding with milk replacer, starter, and alfalfa hay significantly increased thespecies and the abundances of different microbes by using different carbon andnitrogen sources from both fibrous carbohydrate and non-fibrous carbohydrate, whichcould further benefit to the improved digestion, absorption, and immune function ofyaks in barn feeding group.