The effect of dietary CP and NFC different levels on UT-B expression: A meta-analysis

Introduction: As is already known, urea transport across the ruminant wall is mediated via urea transporters in the epithelium membrane (Stewart et al. 2005). Facilitative urea transporters are derived from the UT-A and UT-B genes. UT-B mRNA or protein expressions have been characterized in the rumen epithelium (Ludden et al. 2009; Marini and Van Amburgh 2003; Marini et al. 2004; Stewart et al. 2005). Gene transcript abundance for UT-B is significantly correlated with the ruminal serosal to mucosal urea fluxes. However, the mechanism by which the increased gene expression occurred is unclear (Jin et al. 2018). Transcriptome analysis has been used to analyze the rumen epithelium metabolic pathway changes under various conditions (Baldwin et al 2012; Dionissopoulos et al 2014; Naeem et al 2014). The regulation of these urea transport mechanisms across the rumen wall may be reavealed through this approach. Material and methods: Literature searches were performed through various databases (Google Scholar, PubMed, Medline, Science Direct, Scopus, Web of Science). The keywords used to search relevant studies included: carbohydrate, dietary, protein and urea transporter. Based on the selection criteria, only 11 articles were included in the database for the final analysis. The response variables extracted for the meta-analysis included pH, VFAS, N-NH3 and UT-B expression. Meta-analysis was carried out using the Comprehensive Meta-Analysis package, version 3. The effect sizes of across studies were calculated with fixed and random effect models. The presence of true heterogeneity among studies was identified with Cochran’s Q–tests and quantification of the degree of heterogeneity was done with the I2 index. Possible publication bias was evaluated with funnel plot and statistical tests (Vesterinen et al. 2014). Results and discussion: The results of current meta-analysis showed that different levels of CP in diet, has a positive effect on ruminal N-NH3 concentration and UT-B expression (