Seasonal Changes in Sodium Metabolism in Reindeer (Rangifer tarandus tarandus) in an Inland Area of Norway

Sodium metabolism was studied by isotope dilution techniques infree-ranging reindeer in the Jotunheimen mountain region of southern Norway. In the study three groups of animals were injected intravenously with 22NaCl and bled 2-3 times per year. The study lasted from 184 to 993 d in the groups. Flow rates and half times of 22Na in the plasma pool were calculated. The overall results showed half-times for 22Na in winter of 301 d against 107 d in summer (mid May to early September). The difference in metabolic half time reflected large differences in the Na content of the diet. Sodium analyses of 485 plant samples from the study area, and diets constructed from published literature, showed that 1 kg dried summer diet would contain 6 to 7 mmol Na kgand 1 kg winter diet 4.4 mmol Na kg-~. Daily food intakes were calculated from dietary Na content and Na turnover estimates. Female reindeer with 70 kg body mass had an intake of 3.2 to 3.8 kg dry matter in summer and 1.8 kg in winter. We conclude that the Na supply in our area is marginal for reindeer, and that supplementation may enhance reindeer survival and productivity.