THE EFFECT OF TIMOTHY SILAGE ON THE BACTERIAL POPULATION IN RUMEN FLUID OF REINDEER (RANGIFER TARANDUS TARANDUS) FROM NATURAL SUMMER AND WINTER PASTURE

The seasonal effect of first cut (FC) and regrowth (RG) timothy (Phleu m pratense) silage on the rumen fluid bacterial population and the abi lity of this microbial ecosystem to digest cellulose was compared to t hat of reindeer from natural pasture (NP). FC with 27% leaves containe d 30.4% dry matter (DM) cellulose and 6.2% DM water soluble carbohydra tes (WSC), while RG with 89% leaves contained 18.4% DM cellulose and 3 0.0% DM WSC. The number of culturable anaerobic bacteria per mi rumen fluid on a habitat simulating medium (M8V) ranged between 1.1 X 10(8) and 95.0 X 10(8) in the reindeer (n = 18) investigated, and no signifi cant (P > 0.05) differences were found between animals from NP and ani mals from the experimental groups in summer or winter. Carboxymethyl c ellulose hydrolysing bacterial strains (n = 138) isolated from the rum en fluid of the animals (n = 18) using an acid-swollen cellulose mediu m were characterised as Butyrivibrio spp. (69.6%), Eubacterium spp. (1 .4%), Clostridium sp. (0.7%) and unknowns (28.3%). Cellulolytic strain s of B. fibrisolvens were isolated from only one of the calves, which had been fed RG in summer. The rumen bacterial composition in reindeer on NP resembled that of the experimental groups. In vitro digestibili ty trials demonstrates that the ability of the rumen microbiota to dig est cellulose is generally reduced in reindeer fed silage in summer co mpared to winter. Ruminal malfunction occurred in some of the animals, but no correlation between the composition of the bacterial populatio n in the fluid fraction of the rumen and the ability of this microbiot a to ferment cellulose was found.