Ruminal microbial digestion in free-living, in captive lichen-fed, and in starved reindeer (Rangifer tarandus tarandus) in winter

Abstract

In free-living (FL) reindeer eating a natural mixed winter diet dominated by lichens, captive (CF) reindeer fed pure lichens ad libitum, and CF reindeer subsequently starved for 1 day (CS1 reindeer) or 4 days (CS4 reindeer), the dominant rumen anaerobic bacteria were characterized, their population densities were estimated, and ruminal pH and volatile fatty acid concentrations were determined. In the FL reindeer, the total median viable anaerobic bacterial population ranged from 18 x 108 to 35 x 108 cells per ml of rumen fluid (n = 4), compared with 26 x 108 to 34 x 108 and 0.09 x 108 to 0.1 x 108 cells per ml of tureen fluid in CF reindeer (n = 2) and CS4 reindeer (n = 2), respectively. The median bacterial population adhering to the tureen solids ranged from 260 x 108 to 450 x 108, 21 x 108 to 38 x 108, and 0.5 x 108 to 1.9 x 108 cells per g (wet weight) of rumen solids in FL, CF, and CS4 reindeer, respectively. Although there were variations in the rumen bacterial composition among the FL reindeer (n = 4), strains of Bacteroides, Fibrobacter, Streptococcus, and Clostridium dominated in the tureen fluid. Streptococcus spp. and Clostridium spp. were the dominant bacteria in the CF reindeer (n = 2), while in the CS4 reindeer (n = 2) the dominant bacteria were Fusobacterium spp., members of the family Enterobacteriaceae, and Eubacterium spp. Transmission electron micrographs of lichen particles from the tureen of one FL reindeer, one CF reindeer, and one CS4 reindeer show bacteria resembling Bacteroides spp. adhering to the lichen particles, evidently digesting the lichen hyphae from the inside. The median ruminal volatile fatty acid concentrations and acetate/propionate ratios were 78.9 mmol/liter and 4.0, respectively, in the FL reindeer (n = 4), compared with 66.7 mmol/liter and 3.0 in the CF reindeer (n = 4) and 19.9 mmol/liter and 5.3 in the CS4 reindeer (n = 4). In comparison with a pure lichen diet, a mixed natural winter diet seems to increase the bacterial numbers associated with the rumen solid fraction and to increase tureen fermentation in favor of plant fiber digestion. Starvation greatly reduced the bacterial population densities and changed the bacterial species composition in the rumen.