Digestion of a dehydrated lucerne/barley diet (70:30) in defaunated, Isotricha-monoinoculated and mixed-fauna-inoculated rumen in sheep

Abstract

Two adult Texel sheep fitted with permanent rumen fistulae were defaunated for 12 weeks in a preliminary experiment. They were then reinoculated with Isotricha sp for 11 weeks, and finally with a mixed fauna (Entodinium, Epidinium, Eudiplodinium and Isotricha) for 10 weeks. They were fed a diet composed of dehydrated lucerne (700 g/d), pelleted barley grain (300 g/d), grass hay (100 g/d) and wheat straw (50 g/d) in one daily meal. Isotricha and the ciliates of the mixed fauna developed rapidly, reaching a maximum concentration 9-17 d after inoculation. Their concentration then fell for 2-3 d and finally stabilized at values close to 104/ml for Isotricha, Eudiplodinium and Epidinium and 2.5 × 105/ml for Entodinium. The estimated ciliate biomass in the rumen was 1.8 g l-1 for a volume of 10.2 ml l-1 in the Isotricha-monoinoculated sheep and 4.7 g l-1 for a volume of 25.0 ml l-1 in mixed-fauna-inoculated sheep. The concentration of Isotricha was unaffected by the inoculation of mixed fauna during the third part of the experiment. No difference in total rumen bacteria counts was observed between defaunated, monoinoculated and completely refaunated animals. The total adenylic nucleotide concentration in filtered rumen juice was 4 times higher in faunated sheep just before feeding and 4-9 times lower after feed intake as compared to defaunated animals; the energy charge was always higher in faunated animals. These results are discussed in relation to the digestive activity and biomass of the protozoa. The in situ degradation of lucerne stems was the highest in the mixed-faunated sheep over a retention time interval of 6-18 h. The values obtained in Isotricha-monoinoculated sheep were intermediate between the defaunated and the mixed-faunated states. The digestibility in the whole digestive tract of dietary dry matter, organic matter, nitrogen and neutral detergent fibre was unaffected by the addition of either Isotricha or the mixed fauna in defaunated rumens. The total volatile fatty acid concentration was higher (p < 0.05) in the defaunated sheep between 6 and 18 h after feeding. The molar proportion of butyrate was significantly (p < 0.05) increased by the presence of mixed fauna in the rumen while that of propionate and valerate was lower. A non-significant decrease in acetate was also observed. The concentration of NH3-N in the rumen was significantly increased (p < 0.05) by the presence of the mixed fauna in the rumen but was unaffected or slightly reduced by Isotricha alone. This result is discussed in relation to nitrogen utilization in ruminants. © 1995 Elsevier/INRA.