title: Equine pre-caecal and total tract digestibility of individual carbohydrate fractions and their effect on caecal pH response.
abstract: The working hypothesis was that a minor postprandial caecal pH decline would affect apparent total tract digestibility (ATTD) of the fibre fraction in horses and, hence, that soluble fibre would amplify fermentation and consequently increase ATTD of fibre. This study was a 4 × 4 Latin Square design with a sequence of 17 days adaptation to the ration followed by 8 sampling days. The feed rations consisted of only timothy hay (Group H), hay plus molassed sugar beet pulp combined with either whole oats (Group OB) or barley (Group BB) and hay plus loose chaff based concentrate (Group M). Four horses fitted with permanent caecal cannulas and collection harnesses were used. A pH electrode with logger was inserted through the cannula and caecal pH was recorded at 1 min intervals for 8 h. The mobile nylon bag technique was used to quantify pre-caecal loss (PCL) of individual feedstuffs. Fibre was analysed as dietary fibre (DF), non-starch polysaccharides, soluble non-cellulosic polysaccharides (S-NCP), insoluble non-cellulosic polysaccharide (I-NCP) and neutral detergent fibre. The ATTD of the S-NCP fraction was above 0.8, which was 60% higher than for the I-NCP fraction. The PCL of starch were 0.98 (oats) and 0.75 (barley). The BB diet lowered (p < 0.001) postprandial caecal pH more than the other diets and a significant correlation was found between the lowest pH and ATTD of I-NCP (r = -0.66; p = 0.005). In conclusion, this study successfully measured the in vivo digestibility of individual fibre fractions and found that S-NCP was more digestible than the I-NCP, and that a single meal of unprocessed barley was sufficient to decrease caecal pH to such an extent that the fibre digestibility of the whole diet was negatively affected.
authors.affiliation: Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: Christine
authors.initials: C
authors.lastname: Brøkner
authors.forename: Dag
authors.initials: D
authors.lastname: Austbø
authors.forename: Jon Anders
authors.initials: JA
authors.lastname: Næsset
authors.forename: Knud Erik Bach
authors.initials: KE
authors.lastname: Knudsen
authors.forename: Anne-Helene
authors.initials: AH
authors.lastname: Tauson
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D004032:Diet / Q000662:veterinary; D004040:Dietary Carbohydrates / Q000378:metabolism*; D004063:Digestion / Q000502:physiology*; D005766:Gastrointestinal Contents / Q000737:chemistry*; D041981:Gastrointestinal Tract / Q000502:physiology*; D006736:Horses / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008297:Male
chemical_list: D004040:Dietary Carbohydrates