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 stu dy three groups of animals were injected intravenously with (NaCl)-Na-22 an d bled 2-3 times per year. The study lasted from 184 to 993 d in the groups . Flow rates and half times of Na-22 in the plasma pool were calculated. Th e overall results showed half-times for Na-22 in winter of 301 d against 10 7 d in summer (mid May to early September). The difference in metabolic hal f time reflected large differences in the Na content of the diet. Sodium an alyses of 485 plant samples from the study area, and diets constructed from published literature, showed that I kg dried summer diet would contain 6 t o 7 mmol Na kg(-1) and I kg winter diet 4.4 mmol Na kg(-1). Daily food inta kes were calculated from dietary Na content and Na turnover estimates. Fema le 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 fur reindeer, and that supplementation may enhance reindeer sur vival and productivity.