Oncotic Pressure and the Effects of Water Deprivation in Healthy Captive Asian Elephants

We evaluated the oncotic pressure (plasma colloid osmotic pressure, πc) in a group of healthy, captive Asian elephants ( Elephas maximus; n = 21) with a colloid osmometer with a membrane cutoff of >20,000 daltons. The median πc for these elephants was 26.3 mm Hg with an interquartile interval of 25.5–26.8 mm Hg. The mean πc value was 26.0 mm Hg ± SD 1.1. We found moderate correlation between albumin measured by electrophoresis and πc ( r = 0.622; p = 0.003). After a 16-h water deprivation test in a subset of elephants ( n = 16), a difference in πc was not detected, despite a significant increase in serum total proteins, urea, and osmolality. These results indicate that πc is not a sensitive indicator of hydration status in elephants after a short period of water deprivation. Use of oncotic pressure as a diagnostic tool in diseased Asian elephants warrants further investigation.