Renal clearance and fractional excretion of electrolytes over four 6-hour periods in cattle

Abstract

SUMMARY Four consecutive 6-hour urine sample collections were performed on 7 healthy adult Holstein cows fed a diet of coastal Bermuda hay with ad libitum water consumption. Urine (via indwelling urinary catheter) and venous blood samples were collected at 6, 12, 18, and 24 hours. Total 24-hour urine production for the 7 cows ranged from 4,515 to 7,130 ml/d (mean ± sd, 5,633 ± 946 ml/d) or 0.02 to 0.04 ml/kg of body weight/d (mean ± sd, 0.03 ± 0.007 ml/kg/d). Renal clearance (C) of creatinine (Cr), sodium (Na), calcium (Ca), and magnesium (Mg) varied significantly (P < 0.05) among individuals, but did not vary significantly among the four 6-hour collection periods. Clearance of chloride (CI) and phosphorous (P) did not vary significantly either among individuals or among the four 6-hour periods. Clearance of potassium (K) varied significantly (P < 0.05) among individuals and among the four 6-hour periods. Creatinine clearance was significantly (P < 0.01) correlated with CCI, CCa, CP, and CMg when all data were considered. Significant (P < 0.05) correlations were also found between CCI, and CK, CCa, CP, and CMg; between CCa and CP and CMg; and between CP and CMg. Fractional excretion (fe) of Na, K, CI, Ca, P, and Mg did not vary significantly among the four 6-hour periods. Fractional excretion of Na, Ca, and Mg (P < 0.01) and K and P (P < 0.05) varied significantly within individuals among the 6-hour periods. Mean fe values, calculated by averaging values for each of the 4 collection periods for all 7 cows, ranged from 0.05 to 0.78% for fena; 129.33 to 670.40% for fek; 1.23 to 6.23% for feci; 0.17 to 4.44% for feca; 0.36 to 1.14 for fep; and 4.96 to 11.73% for femg. Linear relationships between the clearance and fractional excretion of electrolytes were observed on base-10 logarithmically transformed data for Na, Ca, P, and Mg. Linear relationship was not found between CK and fek or between CCI and feci.