FASTING EFFECTS ON IN VITRO FERMENTATION PATTERN OF RABBIT CAECAL CONTENTS

Abstract

Caecal contents were collected from six 16h fasted (F) and six non fasted (NF) rabbits, sacrificed between 9 and 1 0am. They were incubated for 24h/39ºC and net productions of volatile fatty acids (VFA) and methane were determined. In a separate preliminary experiment, caecal contents obtained from a F and a NF rabbit were incubated with starch, cellulose or pectins. In F animals, total VFA concentration was lower (P<0.001) and caecal pH significantly higher (P=0.015) than in NF enes: 6.5 vs 6.2. Molar proportions of propionate were higher than butyrate (11.3 vs 4.0%) in F rabbits. However, the latter became higher after 24h of in vitro incubation. Significant (P<0.001) less total VFA (844 vs 1776 µmol/flask) but higher (P=0.003) amounts of methane (271 vs 131 mmoles/mole VFA) were formed using caecal contents from F rabbits. Calculated hydrogen recoveries were indicative of reductive acetogenesis (RA) in NF but not in F animals (49 vs 73%). When one of the substrates was added, effect of fasting was not any more clear for VFA but still for methane and hydrogen recoveries.