MUCIN OUTPUT IN ILEAL DIGESTA OF PIGS FED A PROTEIN-FREE DIET

Daily outputs of mucin in ileal digesta were estimated in three barrow s fed a protein-free diet while administered either saline (SAI) or a complete amino acid mixture (AAI) intravenously. The water soluble-eth anol precipitable fraction of ileal digesta (crude mucin; CM) was used to estimate the composition of mucin in ileal digesta. This fraction exhibited a carbohydrate composition characteristic of mucin and had a high threonine, serine and proline content (40 mol/100 mel). The prop ortions of soluble gastric and intestinal mucins, approximately 27 and 73 %, respectively, were estimated from the N-acetylglucosamine (GlcN Ac)/N-acetylgalactosamine (GalNAc) ratio in CM. The daily outputs of s oluble mucin, 2.75 and 3.41 g/day from SAI and AAI pigs (p = 0.13), re spectively, were determined from the GalNAc outputs in CM, assuming th e above contributions of gastric and intestinal mucins. The estimated soluble mucin outputs accounted for more than 99 % of the fucose, gala ctose, GalNAc and GlcNAc in CM. Total mucin outputs in ileal digesta, 5.32 and 5.65 g/day from SAI and AAI Pigs (p = 0.24), respectively, we re determined from the total GalNAc output in digesta, assuming solubl e and insoluble mucin had similar compositions. Based on these outputs , mucin represented approximately 30, 7 to 22, 15 and II % of the endo genous threonine, proline, serine and protein, respectively, in ileal digesta. Approximately 74, 76, 100 and 53 % of the fucose, galactose G alNAc and GlcNAc, respectively, in ileal digesta from pigs in this stu dy was attributed to mucin. The results from this study demonstrate th e importance of mucin as a source of some endogenous amino acids and c arbohydrates.