A descriptive study of rumen digestion in meroxenic lambs according to the nature and complexity of the microflora.

We studied in meroxenic lambs, i.e. in lambs with a simplified digestive microflora, the effect of the microflora on the quantities of solid feed intake and on the main digestive parameters in the rumen. Axenic lambs were inoculated with a more or less complex flora, obtained by diluting (10(-8), 10(-7), 10(-8) a pool of rumen fluid taken either from young conventional lambs before weaning from adult sheep (Pool A) or from meroxenic lambs (Pool B). A few of these lambs then were inoculated with a genus of protozoa (Entodinium sp. or Polyplastron multivesiculatum). The results show that the main digestive parameters depended on the nature of the inocula which the lambs had received. Food consumption and volatile fatty acid concentration of the rumen fluid, low in lambs inoculated with the 10(-8) dilution, were higher in lambs inoculated with a more complex microflora (10(-6) and 10(-7) dilutions). The VFA concentration measured in these lambs however was approximately two times lower than that observed in conventional animals at the same age and fed the same feed. Food intake and the development of the fermentation pattern were favoured by an early inoculation of the animals. The complexity of the microflora appears to have influenced the composition of the VFA mixture. The latter was found to consist mainly of acetic acid in lambs inoculated with the 10(-8) dilution. In lambs which received the 10(-6) dilution, the composition of the VFA mixture was similar to that observed in conventional lambs. In all animals, except in lambs 10(-8), the ammonia nitrogen concentration of the rumen fluid was found to be higher during the first month after birth (between 100 and 200 mg/l). A subsequent decrease in ammonia nitrogen concentration was observed at two and a half months of age (20 to 40 mg/l). The establishment of protozoa ciliates in the rumen of these lambs was followed by an increase in butyric acid and ammonia nitrogen concentration.