Water intake and excretion, urinary solute excretion and some stress indicators in mink (Mustela vison). 1. Effect of ambient temperature and quantitative water supply to adult males

Thermal environment and water supply are factors which are supposed to influence the performance and well being of farm-raised mink but conclusive literature data are still very limited. The present series of experiments was conducted in order to quantify effects of thermal environment on water intake and excretion, urinary solute excretion and estimate possible stress reactions. Water intake and excretion, urinary osmolality and urinary excretion of sodium (Na), potassium (K), cortisol and catecholamines were studied in a balanced Latin-square design experiment with six adult male mink, kept at three different ambient temperatures (T(a)); (5 degrees C, 20 degrees C and close to 35 degrees C) and given three different water supplies (E: extra water in the food; N: normal ad libitum drinking water supply; R: restricted, free access to drinking water twice daily). The experiment comprised nine periods, each of 3 days. Food apparent digestibility, intake of metabolizable energy (ME), metabolic and evaporative water, oxidation of nutrients and ME requirement for maintenance (ME(m)) were calculated. Water intake was strongly affected by T(a), with dietary water being the major source at 5 degrees C and 20 degrees C, its importance being profoundly exceeded by drinking water at 35 degrees C. Water excretion in urine was highest at the lowest T(a) and lowest at the highest T(a). Restriction of access to drinking water resulted in lower total water intake, and excretion, mainly by decreased urinary volume, reflected by increased urinary osmolality and increased solute concentration. ME intake decreased as T(a) increased but urinary and total water output per kJ ME was not significantly affected by T(a) or water supply. Excretion of Na and K per kJ ME mainly monitored urinary water excretion, being highest under conditions when urine production was highest. Metabolic water made up 0.14 to 0.17 of the total water intake and evaporative loss increased from about 50 to 125 g/kg live weight (M)(0.75) as T(a) increased. ME(m) was lowest (534 kJ/kg M(0.75)) at 20 degrees C, and highest (647 kJ/kg M(0.75)) at 35 degrees C. Cortisol excretion generally tended to increase when water supply was restricted, the increase being significant at 35 degrees C. This, in combination with outer signs of distress in the animals, emphasized that this high temperature in combination with limited access to drinking water exposed the animals to a very stressful situation but rectal temperature remained normal, indicating intact temperature regulation mechanisms.