Urine specific gravity and urine osmolality in healthy pet rabbits (Oryctolagus cuniculus)

Abstract

Renal concentrating ability in mammals can be evaluated by determining either urine specific gravity (Usg) or urine osmolality (Uosm). However, in rabbits, reference ranges are currently lacking for Uosm, and considered wide and aspecific for Usg. This study therefore aimed to establish reference ranges for both parameters as well as study their correlation and potential effects of gender, age and weight category of the rabbit, and the method and time of the sample collection. For this purpose, morning and evening urine samples as well as an additional blood sample were collected from 80 healthy privately-owned breeder rabbits. Usg and Uosm were subsequently measured using respectively clinical refractometry and freezing-point osmometry.

Findings of this study reveal a wide reference range for Usg (1.010-1.061) and Uosm (130-2154 mOsm/kg). A strong correlation was present between both parameters (Pearson correlation coefficient: 0.91). Mixed model analysis and logistic regression revealed no influence of gender or age, whereas time and method of urine collection were found to exert a small but significant effect on Usg and Uosm, respectively. Weight category greatly influenced both Usg and Uosm, with dwarf breeds showing significantly higher values for both parameters. These results suggest that weight category needs to be taken into account when evaluating Usg or Uosm. However, due to potential bias with other factors such as breed and origin of the rabbits further research is warranted prior to drawing definite conclusions.