Diet composition, rumen papillation and maintenance of carcass mass in female Norwegian reindeer (Rangifer tarandus tarandus) in winter

The uptake of volatile fatty acids (VFAs) from bacterial fermentation of fo rage in the rumen is enhanced by the presence of papillae which greatly inc rease the surface area of the mucosa of the rumen. The degree of papillatio n, expressed as the surface enlargement factor (SEF), seems to be closely r elated to the level of microbial activity and the rate of production of VFA s in the rumen. In several species of wild ruminants the SEF decreases mark edly in winter, apparently in response to a decrease in the quality and ava ilability of forage and also, presumably, in the level of ruminal microbial activity. Contrary to expectation, however, no reduction in the rate of pr oduction of VFAs in winter has been detected in semi-domesticated reindeer at natural pasture in northern Norway. We investigated the body mass, the c omposition and quality of the diet and the morphology of rumen papillae in adult female reindeer free-living at natural pasture. Animals were slaughte red in matched aged groups of nine on four occasions: in autumn (September) and winter (November, February and March). The composition and quality of the diet was determined by morphological and chemical analysis of plant fra gments recovered from the rumen. The carcass mass of the animals did not di ffer significantly between collections. The animals ate vascular plants and lichens from 37 different genera. The composition of the diet varied littl e between months except for the inclusion of a substantial proportion (25.8 % of fragments) of lichens in March. The mean density of rumen papillae inc reased from 55.6 papillae/cm(2) in September to 75.7 papillae/cm(2) in Marc h (P < 0.001). All other parameters, including the length and perimeter of the papillae and the SEF of the rumen, were lower in March compared with Se ptember. However, the mean SEF increased from 8.8 in February to 10.6 in Ma rch (P < 0.05), indicating increased ruminal fermentation in late winter. W e propose that the increase in the SEF in March might be associated with th e increase in the proportion of lichens in the diet. Lichens are highly dig estible in reindeer but do not score highly in conventional analyses of die t quality owing to the unusual chemical structure of the structural carbohy drates of which they are composed.