LAUSR

Development of a properly functioning gastrointestinal tract (GIT) at an early age is critical for the wellbeing and lifetime productivity of dairy cattle. The role of early microbial colonization on GIT development in neonatal cattle and the associated molecular changes remain largely unknown, particularly for the small intestine. In this study, we performed artificial dosing of exogenous rumen fluid during the early life of the calf, starting at birth through the weaning transition at eight weeks. Six calves were included in this study. At 8 weeks of age, tissue from the ileum were collected and subjected to host transcriptome and microbial meta-transcriptome analysis using RNA-sequencing. A total of 333 genes showed significant differential expression (DE) (fold-change ³2; adjusted P<0.1, mean read-count ³10) between the treated and control calves. Gene ontology analysis indicated that these DE genes were predominantly associated with processes related to the host immune response (P < 0.0001). Association analysis between the host gene expression and the microbial genus abundance identified 57 genes as having significant correlation with the ileum microbial genera (P < 0.0001). Of these, three genes showed significant association with six microbial genera: lysozyme 2 (LYZ2), fatty acid binding protein 5 (FABP5) and fucosyltransferase (FUT1). Specifically, the profound increase in expression of LYZ2 in treated calves suggested the activation of anti-bacterial activity and innate response from the host. Despite the limitation of relatively small sample size, this study sheds light on the potential impact of early introduction of microbes on the small intestine of calves.