In contrast to virtually all other species of ruminants, reindeer (Rangifer arandus) eat substantial amounts of lichens in winter. Several different species of lichens are eaten and most are highly palatable. The chemical composition and the in vitro digestibility of six species of terricolous lichens commonly eaten by reindeer were measured. Ruminal inoculum was obtained in winter from six free-ranging reindeer that had been grazing on natural pastures in northern Norway. Analysis of the plant parts recovered from their rumens confirmed that the animals had been eating a mixed diet that included both lichens and vascular plants. The chemical composition and the in vitro digestibility of the different species of lichens varied considerably between species and genera. Cetraria islandica, C. nivalis and Cladonia arbuscula were highly digestible [69-77% dry matter (DM)], Stereocaulon paschale was poorly digestible (43% DM), whereas Cladonia stellaris and C. gradlis had an intermediate digestibility (56-57% DM). Mixing ladonia stellaris with vascular plants (50:50) had no effect on the in vitro digestibility of the combined substrates. The in vitro digestibility of Cladonia stellaris in inoculum from two captive reindeer which had had no access to lichens was very low (10% DM). This shows that the source of inoculum used for digestibility trials has a major effect on the apparent digestibility of the substrates. Evidently, the extent to which reindeer are able to utilize lichens depends on the species that are selected and on what the animals have been eating recently.

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Transport of 22Na and 14C-butyrate across the ruminal epithelium of captive reindeer fed a concentrate diet in summer (n=5) and in winter (n=5) and from free-ranging reindeer taken from summer (n=3) and winter pasture (n=5) was measured in vitro in Ussing chambers. Significant amounts of both Na+ and butyrate were transported across the isolated epithelium without any external driving force. The ruminal transport of Na+ and butyrate were interacting, as evidenced by both the observed amiloride-induced reduction of net butyrate-transport and by the positive correlation between net transport of butyrate and Na+. Amiloride also reduced the net transport of Na+ without significantly affecting the short-circuit current, indicating the presence of an apical Na+/H+ exchanger in the ruminal epithelium of reindeer. The captive reindeer increased the dry matter intake of a constant quality concentrate from winter to summer, but this neither affected their ruminal transport capacity nor their ruminal surface enlargement factor (SEF). Free-ranging reindeer increased their ruminal transport capacity for Na+ and butyrate from summer to winter but simultaneously reduced their ruminal SEF. The present data indicate that this food-induced increase in transport capacity was attributed to changes in the nutrient composition of the diet.

The marginal winter pastures of reindeer and caribou (Rangifer tarandus) in Arctic and sub-Arctic areas are assumed to be nitrogen-and mineral-poor. Reindeer eat a mixed diet consisting of nitrogendeficient lichens and a wide variety of vascular plants in winter. Some reindeer populations manage to maintain carcass mass outside the growing season and very little is known about the ability of reindeer to utilize vascular plants in this season. The chemical composition and in vitro digestibility of 17 species of vascular forage plants and one species of moss collected mid-winter from beneath the snow at an inland winter pasture in northern Norway were determined. Wintergreen parts of graminoids had a high content of crude protein (0n072-0n108 g\kg dry matter (DM)) and watersoluble carbohydrates (0n098-0n167 g\kg DM) and were highly digestible (50-65 % IVDMD) compared with the withered parts of the plants (27-53 % IVDMD). The digestibility of both shrubs and graminoids was inversely related to content of cellulose and lignin, but positively correlated with increasing contents of water-soluble carbohydrates. Shrubs were relatively calcium-rich (3n6-6n1 g\kg DM) while wintergreen graminoids contained up to 10n0 g\kg DM of potassium, 1n5 g\kg DM magnesium and 2n1 g\kg DM phosphorus. The present study demonstrates that the wintergreen parts of several species of vascular plants are nutritious, containing high levels of nitrogen and minerals, and that they are highly digestible to reindeer in winter. Vascular plants may, therefore, be more important to reindeer and caribou in winter than previously realized.

Management of semi-domesticated reindeer (Rangifer tarandus tarandus) in the northern regions have historically focused on reindeer–vegetation interactions, while few data on the food intake of these animals exist. Dry matter intake (DMI) was therefore estimated successively during winter in reindeer calves fed (i) ad libitum pelleted reindeer feed (RF-80; n=6), (ii) fed ad libitum mixed lichens (n=6) and (iii) in free-ranging reindeer calves (n=3) on natural winter pasture (March/April; 69 °N). Faecal output, determined with faeces collection bags, was 24±4, 6±3 and 22±3 g DM/day/kg BM0·75 in reindeer fed RF-80, mixed lichens and on winter pasture, respectively. Actual DMI of reindeer in captivity fed RF-80 and mixed lichens was 70±10 g DM/day/kg BM0·75 and 27±8 g DM/day/kg BM0·75, respectively. The DMI of the captive reindeer calves was accurately estimated on both diets on the basis of the digestibility of their diet and their faecal output. Using the same method, the DMI of free-ranging reindeer calves on natural winter pastures in northern Norway was estimated to be 34–61 g DM/day/kg BM0·75. The present study discusses factors that influence the food intake of reindeer in winter with emphasis on the seasonal regulation of appetite and DMI in these Arctic ruminants.