Water and electrolyte balance in male mink (Mustela vison) on varying dietary NaCl intake.

The effect of a ten-day dietary sodium load on the fluid balance of mink was studied by adding to the food NaCl 0.5, 1 or 2% of the wet weight. The basic diet without salt addition contained sodium corresponding to 0.5% NaCl of the wet weight. The animals showed no signs of discomfort, eating well in all test groups. Adding of 0.5% salt to the food did not increase drinking of water, whereas 1 and 2% salt addition doubled and quadrupled water consumption, respectively. Urine excretion was slightly higher than consumption of drinking water, and both increased parallelly to increasing salt intake. The dietary salt excess was mainly excreted in urine, whereas the alimentary canal played only a minor role. Urine sodium concentration rose with increasing salt intake, peak concentration 350 mM being reached in the diet with 1% salt addition. On higher sodium load any further increase in renal sodium excretion was achieved only by increasing the volume of urine. Urine osmolality was slightly above 2000 mOsm/kg on the control diet and on the diet with 0.5% salt addition. More diluted urine was excreted on higher salt loads, urine osmolality being 1500 mOsm/kg on the diet with 2% salt addition. Healthy minks appear to tolerate considerably high concentrations of salt in the feed. However, a sufficient supply of drinking water is of critical importance, because increased water intake and renal sodium excretion are the main means of eliminating excess salt.