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Rumen Epithelial Gene Expression in Periruminant Holstein Bull Calves Fed a Fermentation Extract of Aspergillus oryzae
A fermentation extract of Aspergillus oryzae has previously been utilized as a direct fed microbial (DFM) to promote starter intake and feed efficiency in calves. Potential effects of this DFM on rumen epithelial gene expression are unknown and may help explain some benefits of supplementation. The objective was to determine if age and dietary inclusion of an extract of A. oryzae alter relative abundance of select rumen epithelial genes in periruminant Holstein bull calves. The genes investigated encode proteins that specialize in: VFA transport (MCT1, MCT2, MCT4), intracellular regulation of pH (NHE1, NHE2, NHE3, DRA, PAT1) and epithelial barrier function (GJA1, CLDN1). Individual calves (n=52) were randomly assigned to a slaughter age, 4 wk (n = 16) or 8 wk (n = 36), and treatment, control (CON; n = 27) or direct fed microbial (DFM; n = 25). Calves were housed with no bedding and fed individually. Liquid DFM was delivered in milk replacer (2 g per day) for the first 4 wk of the trial; solid DFM (2 g per day) was top-dressed on grain thereafter. Calves were fed non-medicated milk replacer twice daily (22.0% CP, 20.0% fat DM basis; 680 g/d) and had ad libitum access to texturized grain (20% CP, 2.0% fat) and water. At slaughter, rumen tissue was obtained from the cranial ventral region of each calf; the epithelial portion was separated and preserved for later RNA extraction and cDNA synthesis. cDNA was used in quantitative reverse transcription PCR assays. UXT, RPS9, RPS15, and RPS26 were endogenous control genes. All transcripts were detectable in all calves. Relative mRNA abundance of NHE3 was shown to decrease with age (P<0.05); no other genes were affected by age or treatment. In summary, dietary inclusion (2g/d) of an extract of A. oryzaedid not result in altered rumen epithelial gene expression when supplemented animals were compared to cohorts not fed DFM. More differences were expected due to age as selected genes are related to metabolic development of the rumen, but it is important to point out that gene level data do not always correlate with protein abundance. Further, it is possible that the dose used here was not high enough to elicit treatment effects. Regardless, we provide new data about ruminal gene expression in periruminant dairy calves.
Keywords: dairy calf, rumen, gene expression