Replacing corn grain with corn gluten feed: Effects on the rumen microbial protein synthesis, functional bacterial groups and epithelial amino acid chemosensing in growing goats

Corn gluten feed is rich in crude protein and has been widely used in ruminant diets as an economical substitution for corn grain. This study was conducted to assess the effect of corn grain replaced with corn gluten feed on the ruminal microbial protein (MCP) synthesis, amino acid profile, and mucosal amino acid chemosensing pathway in growing goats, as well as the related mechanisms involved in the ruminal nitrogen metabolism. Twenty male healthy goats with similar body weight (14.5 ± 2.2 kg) and age (1.2 ± 0.2 yr) were randomly assigned to either a corn gluten diet (CGF, 500 g/kg DM) or a corn grain diet (CRN, 500 g/kg DM) (n = 10/diet). The results showed that compared with the CRN diet, goats fed with CGF diet had greater (P < 0.05) crude protein (CP) intake and CP digestibility, but lower dry matter digestibility than those fed CRN diet. The ruminal pH and ammonia levels in goats fed CGF diet were higher (P < 0.05) than those fed CRN diet, while ruminal MCP concentration was lower in goats fed CGF diet (P < 0.05). The copy numbers of ruminal total bacteria (P < 0.05), Provotella ruminicola (P < 0.05), Selenomonas ruminantium (P < 0.05) and Ruminococcus flavefaciens (P < 0.05) were decreased by CGF substitution. No remarkable differences (P> 0.05) were noted for the copy numbers of other well-known amylolytic and cellulolytic bacteria, and free amino acids (FAAs) in the rumen fluids between the two diets. In respect to mucosal amino acid chemosensing pathway, no significant differences (P > 0.05) were observed in mucosal FAAs profile, mRNA expression of anionic, neutral and cationic amino acid transporters, as well as concentration of second messengers in the ruminal mucosa in goats fed the diets. In summary, in response to CGF substitution, dietary CP was preferred to be accumulated in ammonia, and lower ruminal bacteria number decreased ruminal MCP synthesis. Further, CGF substitution did not suppress mucosal amino acid chemosensing system, along with elevated ruminal pH, indicating that the CGF is a better alternative when formulating diets for growing goats.