Nitrogen and in vitro fermentation of nitrogenous substrates in caecal contents of the pig

Abstract

Caecal contents of four 28-week-old pigs were analysed and used as inocula of cultures supplied with plant proteins (gluten, gliadin, zein), mucin, ribonucleic acid (RNA) and glucose Pigs were fed ad libitum a 14.1% crude protein diet containing barley, wheat, wheat bran, extracted soybean meal and a feed supplement. The caecal digesta contained dry matter, total N, protein, trichloroacetic acid (TCA)-soluble N and NH3-N at 120, 3.1, 14.9, 0.64 and 0.27 mg/g (on average), respectively. One g of the caecal content contained 70 μmol of glycine equivalents of amino acids in TCA-soluble fraction. Peptides rather than amino acids were the primary component of the TCA-soluble ninhydrin-reactive material in the caecum. Fermentation of mucin yielded more volatile fatty acids (VFA) than fermentation of other nitrogenous substrates. Zein was the least fermentable substrate tested. Acetate was the principal fermentation end-product, followed by propionate and butyrate. Fermentation pattern differed in cultures grown on glucose and proteins: propionate molar proportions were higher and those of branched-chain VFA lower in former cultures than in cultures supplied with gluten, gliadin and zein. Low proportions of branched-chain VFA were also in VFA produced from mucin and RNA. It can be concluded, therefore, that caecal microorganisms convert nitrogenous substrates, which would be lost in faeces, into valuable products (VFA), utilizable by the host.