Characterization of the Microbial Communities along the Gastrointestinal Tract in Crossbred Cattle

SIMPLE SUMMARY: Crossbreeding has been used worldwide to improve milk production, milk composition, and reproduction performance. Understanding the structure of the microbial communities in the gastrointestinal tract (GIT) of crossbred cattle is paramount for developing new livestock management technologies with an emphasis on nutrition and sustainability. In this study, we investigated the gastrointestinal microbiota of Simmental × Holstein crossbred cattle using 16s rRNA gene sequencing. Microbial communities in the small intestine had the lowest diversity of bacteria and highest diversity of bacterial functions, and three groups of GIT regions, including the stomach, small intestine, and large intestine were characterized by specific bacteria and bacterial functions. In summary, spatial heterogeneity of the microbiota was found across the GIT of crossbreeds, and specific microbial biomarkers were identified in different regions. ABSTRACT: The gastrointestinal microbiota greatly affects the health status and production performance of bovines. Presently, many studies have used high-throughput sequencing methods to investigate the gastrointestinal microbiome in bovines. However, the microbiome profile of crossbred cattle across the whole gastrointestinal tract (GIT) has not been thoroughly reported. In this study, the digesta at ten regions (including the rumen, reticulum, omasum, abomasum, duodenum, jejunum, ileum, cecum, colon, and rectum) of the GIT were collected in three Simmental × Holstein crossbred heifers aged 17 months, and microbial DNA was extracted and amplified for sequencing of the V3–V4 regions of the 16S rRNA gene. Functional orthologs of the microbiota genome were predicted and analyzed. We found that samples were categorized into three groups (the stomach, small intestine, and large intestine) by principal coordinate analysis (PCoA) based on Bray–Curtis dissimilarity in both the bacterial composition and functional profile. Samples from small intestine had the lowest alpha diversity of bacteria composition and highest alpha diversity of the functional composition. Three groups of GIT regions were characterized by several microbiome features. The stomach was characterized by Bacteroidetes and Fibrobacteres at the phylum level, and KEGG pathways related to the metabolism of cofactors and vitamins, glycan biosynthesis, and metabolism were enriched in the stomach. The small intestine was characterized by Actinobacteria and Patescibacteria at the phylum level, and KEGG pathways related to xenobiotics biodegradation and metabolism were enriched in the small intestine. The large intestine featured Ruminococcaceae, Rikenellaceae, and Bacteroidacea at the family level, and KEGG pathways, including steroid hormone biosynthesis, linoleic acid metabolism, and cysteine and methionine metabolism were enriched in the large intestine. The results of the current study revealed the spatial heterogeneity of microbiota across the GIT in Simmental × Holstein crossbreeds and identified microbial biomarkers of different regions. The results can provide useful information for the study of the gastrointestinal microbiome in bovines.