High versus low protein diets to mink - Postprandial plasma urea and creatinine response, osmotic load and pattern of nitrogen and electrolyte excretion

Nitrogen balance, pattern of excretion of nitrogenous end-products, endogen ous urinary N excretion, postprandial plasma urea and creatinine, osmotic l oad, urinary electrolyte excretion and water intake/output relationships we re studied in 12 adult female mink fed a high protein diet (HP; n = 6) prov iding about 155 g protein/kg or a low protein diet (LP; n = 6) providing ab out 95 g protein/kg. Two balance periods of each 3 d were used and diets we re fed raw or cooked. After the last balance period followed a 48 h fasting period. Postprandial plasma urea and creatinine were studied for 48 h foll owing a test meal given after an overnight fast. Osmotic load was determine d based on collection of non-acidified urine carried out during 48 h, Level of protein supply did not affect N balance, being close to zero, whereas s lightly negative balances were achieved for fasting animals. Protein supply was clearly reflected in excretion of urinary urea and allantoin but not i n creatinine and uric acid. Endogenous urinary N excretion was estimated by a second order regression equation giving an intercept of 280 mg/kg(0.75). Post-prandial plasma urea concentrations were strongly influenced by prote in supply, HP animals having substantially higher peaks than LP animals, bu t values returned to fasting values within 24 h after the test meal. Plasma creatinine followed a biphasic pattern with a peak about 2 h after feeding and a nadir approximately 6 h after feeding. Physical form of diet influen ced postprandial urea, animals fed raw diets having a higher peak, but not creatinine. The HP diet provided almost the double osmotic load of the LP d iet and a corresponding increase in urine volume. The resulting water balan ces were identical irrespective of diet, showing that water intake/output r elationships are very accurately regulated.