Short communication: A high-grain diet entails alteration in nutrient chemosensing of the rumen epithelium in goats

Gastrointestinal nutrient chemosensing plays an indispensable role in the regulation of nutrient absorption and the maintenance of metabolic homeostasis in mammals. The aim of this study was to investigate the integrated and distinct mechanisms that sense and transport carbohydrates, lipids and amino acids (AAs) in response to high grain (HG) challenge in the rumen epithelium (RE) of goats. Twelve adult Liuyang black goats were randomly allocated to an HG diet (concentrate/hay, 90:10) or a control diet (CON, concentrate/hay, 55:45). Immunohistochemistry was used to detect alterations in the expression of nutrient transporters and sensing receptors and rumen morphology. The results showed that HG challenge increased ruminal total short chain fatty acid (SCFA) concentrations (P < 0.01), and shifted rumen fermentation towards propionate production. Moreover, compared to the CON group, the HG group exhibited greater expression (P < 0.01) of carbohydrate transporters GLUT2 and SGLT2, long chain fatty acid (LCFA) transporter CD36 and SCFA receptor GPR43, as well as neutral AA transporters EAAT3, LAT2 and rBAT in the RE. However, the expression levels of the carbohydrate transporters GLUTS, GLUT12, SGLT3, 4 F2hc and CAT2 between these two treatment groups were similar (P > 0.05). Morphological analysis indicated that the HG diet notably improved the height, width and surface area of rumen papillae (P < 0.01). In summary, these findings indicate that feeding HG diets to ruminants enhances the chemosensing of carbohydrates, fatty acids and neutral AAs, as well as inducing enlargement of the papillae of the RE.