Seasonal changes in total body water, extracellular fluid, and blood volume in grazing reindeer

The effects of climatic and nutritional changes on body fluid compartmentalization and turnover were investigated in grazing female reindeer. Total body water volume and turnover, extracellular fluid volume, and blood volume were estimated using tritiated water, sodium sulfate-35S, and sodium chromate-51Cr, respectively. During winter and spring, body weights were either maintained or reduced while total body water (percentage of body weight) increased, resulting in appreciable losses of total body solids. In summer, large gains in body weight were accompanied by reduced total body water volumes resulting in substantial increases in body solids. An apparent fluid shift from the intravascular to the extracellular compartment during late spring suggested the occurrence of a starvation edema. Mean water flux rates (ml/day per kilogram body weight) were higher in late spring than during other seasons; lowest values were recorded in early winter. Seasonal variations in nutritional status as reflected by body composition and fluid compartmentalization, and changes in water turnover are discussed in relation to climate and the quality and availability of forage. The complicating influences of pregnancy and lactation are also considered.