Clinical utility of urine specific gravity, electrical conductivity, and color as on-farm methods for evaluating urine concentration in dairy cattle.

Background: Urine concentration (UC) provides clinically useful information concerning hydration status and renal function of animals.

Objectives: To characterize the clinical performance of urine specific gravity measured by optical refractometry (U ) or Multistix-SG urine reagent dipstick (U ), urine electrical conductivity using an OAKTON Con 6 conductivity handheld meter (U ), urine color (U ) using a custom-designed 8-point color chart, and urine creatinine concentration (U ) for assessing UC in dairy cattle.

Animals: 20 periparturient Holstein-Friesian cows.

Methods: Urine was obtained by perineal stimulation or urethral catheterization and urine osmolality (U , reference method), U , U , U , U , and U determined. Diagnostic test performance was evaluated using Spearman's rho and logistic regression to determine the area under the receiver operating curve (AUC) and optimal cut point for diagnosing hypohydration (U ≥800 mOsm/kg). P < .05 was considered significant.

Results: The best performing test for diagnosing hypohydration was U (AUC = 0.90) at an optimal cut point ≥1.030. The second-best performing test was U (AUC = 0.82) at a cut point of ≥23.7 mS/cm, followed by U (AUC = 0.76) at a cut point of ≥95.3 mg/dL, and U (AUC = 0.74) at a cut point of ≥4 on an 8-point scale. Urine specific gravity measured by dipstick performed poorly (AUC = 0.63).

Conclusions And Clinical Importance: U and U provide practical and sufficiently accurate methods for measuring UC in dairy cattle. Urine color had moderate clinical utility as a no-cost cow-side method for assessing UC, whereas dipstick refractometry is not recommended for assessing UC.