Pigs' gastrointestinal microflora provide them with essential amino acids

Abstract

The synthesis of essential amino acids by the gut microflora of pigs, and their absorption, were assessed from the incorporation of 15N from dietary 15NH4Cl and of 14C from dietary 14C-polyglucose into amino acids in the body tissues of four pigs. Both 15N and 14C were incorporated into essential amino acids in body protein. Because pig tissues cannot incorporate 15N into lysine or 14C into essential amino acids, the labeling of these amino acids in body protein indicated their microbial origin. The absorption of microbial amino acids was estimated by multiplying the total content of each amino acid in the body by the ratio of the isotopic enrichment of the amino acid in the body to that in microbial protein. Because the ratio of 14C:15N in body lysine was closer to that in the microflora of the ileum than to that of the cecum, absorption was assumed to take place exclusively in the ileum. The estimates of microbial amino acid absorption from 14C-labeling were as follows (g/d): valine 1.8, isoleucine 0.8, leucine 2.0, phenylalanine 0.3 and lysine 0.9, whereas for lysine, the estimate from 15N-labeling was 1.3 g/d. We conclude that the gastrointestinal microflora contribute significantly to the amino acid requirements of pigs.