Effects of the dietary protein level on the microbial composition and metabolomic profile in the hindgut of the pig

The aim of this study was to investigate the effects of a long-term low protein diet on the microbial composition and metabolomic profile in the hindgut of the pig. Thirty-six Duroc × Landrace × Large White growing barrows (70 days of age, 23.57 ± 1.77 kg) were randomly allocated to normal protein diet (NP) and low protein diet (LP) groups using a randomized block design. At the age of 170 days, the digesta in the hindguts of the pigs were collected for microbial and metabolomic analysis. The results showed that there were no significant differences in the average daily gain, average daily feed intake, or feed:gain ratio between the NP and LP groups. The concentrations of isobutyrate, isovalerate, and branched-chain fatty acids (BCFAs)/short-chain fatty acids (SCFAs) in the cecum decreased with the reduction of dietary protein. Pyrosequencing of the V1–V3 region of the 16S rRNA genes showed that LP diet significantly decreased the relative abundance of Lactobacillus in the cecum, and Streptococcus in the colon; however, the relative abundance of Prevotella and Coprococcus in the LP group was significantly higher than in the NP group in the cecum, and Sarcina, Peptostreptococcaceae incertae sedis, Mogibacterium, Subdoligranulum, and Coprococcus was higher in the colon. The gas chromatography–mass spectrometry (GC–MS) analysis showed that the dietary protein level mainly affected phenylalanine metabolism; glycine, serine, and threonine metabolism; the citrate cycle; pyruvate metabolism; and the alanine, aspartate, and glutamate metabolism. Moreover, the correlation analysis of the combined datasets revealed some potential relationships between the colonic metabolites and certain microbial species. These results suggest that a low protein diet may modulate the microbial composition and metabolites of the hindgut, without affecting the growth performance of pigs; however, potential roles of this modulation to the health of pigs remains unknown.