title: Nondietary Gut Materials Interfere with the Determination of Dietary Fiber Digestibility in Growing Pigs When Using the Prosky Method.
abstract: BACKGROUND
  Reported negative ileal and total tract dietary fiber (DF) digestibility values are physiologically untenable and suggest the presence of nondietary material in the gut contents that interferes with the DF determination.
  
  
  OBJECTIVE
  The objective of this study was to demonstrate the importance of interfering material (IM) when the Prosky method was used to determine DF digestibility.
  
  
  METHODS
  Fourteen pigs (41.6 ± 3.0 kg) were surgically implanted with ileal T-cannulas. A semisynthetic fiber-free diet and 2 semisynthetic diets containing kiwifruit as the sole fiber source [25 or 50 g fiber/kg dry matter (DM)] were prepared. Titanium dioxide was used as an indigestible marker. Pigs were fed the kiwifruit-containing diets (n=7 per diet) for 44 d, followed by the fiber-free diet (n=14) for 7 d. Ileal digesta and feces were collected over 3 d, starting on days 42 and 49. The flow of IM and the soluble, insoluble, and total DF digestibility were determined.
  
  
  RESULTS
  Considerable amounts of IM were present when the Prosky method was applied to ileal digesta (12 g/kg DM intake) and feces (28 g/kg DM intake) collected from pigs fed the fiber-free diet after adaptation to the diet containing 50 g/kg DM of fiber. The pigs adapted to the highest fiber concentration had 0.9- and 0.7-fold greater ileal and fecal IM flows than their counterparts adapted to the lowest concentration. In the ileal digesta, crude mucin was the main IM source in the soluble DF fraction (66%). In the ileal digesta and feces, microbial cells were the main IM source in the insoluble DF fraction. The determined ileal soluble DF and total tract insoluble DF digestibilities increased by 44-54% and 78% respectively after correction for IM (P < 0.001).
  
  
  CONCLUSIONS
  Large amounts of IM are present in ileal digesta and feces of pigs when fiber is determined with the Prosky method, leading to a marked underestimation.
authors.affiliation: Riddet Institute, Massey University, Palmerston North, New Zealand c.montoya@massey.ac.nz.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Montoya
authors.affiliation: Riddet Institute, Massey University, Palmerston North, New Zealand.
authors.forename: Shane M
authors.initials: SM
authors.lastname: Rutherfurd
authors.affiliation: Riddet Institute, Massey University, Palmerston North, New Zealand.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Moughan
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D004032:Diet / Q000662:veterinary; D004043:Dietary Fiber / Q000032:analysis / Q000378:metabolism*; D004063:Digestion / Q000502:physiology*; D005766:Gastrointestinal Contents / Q000737:chemistry*; D008297:Male; D013552:Swine / Q000254:growth & development*
keywords: dietary fiber; fiber digestibility; growing pig; interfering material; kiwifruit