Clinically normal dogs were evaluated in states of dehydration, euhydration, and after fluid administration to determine effects of hydration state on renal clearance values. Endogenous creatinine, exogenous creatinine, and [(14)C]inulin clearances, were determined to measure glomerular filtration rate (GFR); in some experiments p-aminohippurate clearance was determined to measure renal plasma flow. Dehydration caused significant (P < 0.05) decrease in clearance values, compared with euhydration, and clearance values during euhydration were significantly (P < 0.05) less than values obtained after a single gavage with water (30 ml/kg of body weight). Sustained administration of 3 fluid regimens was evaluated for effects on clearance values (treatment A = 30 ml of lactated Ringer's solution/kg/h; treatment B = 30 ml of water/kg by gavage hourly; treatment C = 10 ml of glucose:lactated Ringer's solution/ kg/h). All regimens of fluid therapy caused significant P < 0.05), progressive increases in GFR, but treatment C resulted in the most stable GFR values. Increases in clearance values were associated with positive fluid balance; the rate of fluid administration was greater than the rate of urine formation. Data from 285 GFR determinations on 85 dogs were evaluated retrospectively. For each determination, three 20-minute urine collections were made beginning 40 minutes after 30 mi of water/kg was given by gavage. Values between collections were significantly (P < 0.05) different, but varied by < 3%. Comparison of methods for measurement of GFR indicated that endogenous creatinine clearance and [14)C]inulin clearance were highly correlated (R(2) = 0.82), but mean clearance values were markedly different (mean +/- SEM, 28.70 +/- 0.01 and 37.07 +/- 1.29 ml/min, respectively). Exogenous creatinine clearance and [(14)C]inulin clearance were highly correlated (R(2) = 0.95), and mean values were 40.54 +/- 0.70 and 41.02 +/- 0.70 ml/min respectively. We conclude that: state of hydration has a marked effect on GFR; rate of fluid administration that exceeds rate of urine production results in progressive increases in GFR; a single water gavage of 30 ml/kg gives stable GFR values for three 20-minute collection periods, may avoid subclinical states of dehydration, and facilitates accurate urine collections; and endogenous creatinine clearance, as conducted in this study, does not accurately measure GFR.

Four balance trials were conducted in 3 groups of 5 calves each at 0, 4, 8, and 14 weeks after initial inoculation with Ostertagia ostertagi. Group-1 calves were inoculated with 100,000 third-stage larvae (L3) of O. ostertagi/wk for 14 weeks. Group-2 calves were inoculated with 10,000 L3/wk for 14 weeks, and group-3 calves were not inoculated. Effects of infection on apparent digestibilities of dry matter and nitrogen, and balances of nitrogen and water were evaluated. Neither clinically apparent (group 1) nor subclinical (group 2) O. ostertagi infections had observable effects on the apparent digestibility of dry matter. Subclinical infection also had no significant effects on nitrogen digestibility or nitrogen and water balance. Clinically apparent infection, however, decreased the apparent digestibilities of nitrogen significantly (P < 0.05) at 4, 8, and 14 weeks after inoculation, and decreased nitrogen balance at 4 and 8 weeks after inoculation. Group-1 calves also had lower water intake, fecal-water excretion, and apparent water balance, but higher urinary water output at 4, 8, and 14 weeks after inoculation.