The effect of timothy silage on the bacterial population in rumen fluid of reindeer (Rangifer tarandus tarandus) from natural summer and winter pasture

Abstract

The seasonal effect of first cut (FC) and regrowth (RG) timothy (Phleum pratense) silage on the rumen fluid bacterial population and the ability of this microbial ecosystem to digest cellulose was compared to that of reindeer from natural pasture (NP). FC with 27% leaves contained 30.4% dry matter (DM) cellulose and 6.2% DM water soluble carbohydrates (WSC), while RG with 89% leaves contained 18.4% DM cellulose and 30.0% DM WSC. The number of culturable anaerobic bacteria per ml rumen fluid on a habitat simulating medium (M8V) ranged between 1.1×108 and 95.0×108 in the reindeer (n=18) investigated, and no significant (P>0.05) differences were found between animals from NP and animals from the experimental groups in summer or winter. Carboxymethyl cellulose hydrolysing bacterial strains (n=138) isolated from the rumen fluid of the animals (n=18) using an acid-swollen cellulose medium were characterised as Butyrivibrio spp. (69.6%), Eubacterium spp. (1.4%), Clostridium sp. (0.7%) and unknowns (28.3%). Cellulolytic strains 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 digestibility trials demonstrates that the ability of the rumen microbiota to digest cellulose is generally reduced in reindeer fed silage in summer compared to winter. Ruminal malfunction occurred in some of the animals, but no correlation between the composition of the bacterial population in the fluid fraction of the rumen and the ability of this microbiota to ferment cellulose was found.