Journal of Applied Physiology, Vol 71, Issue 1 112-117, Copyright © 1991 by American Physiological Society
Water homeostasis in desert-dwelling horses
J. C. Sneddon, J. G. van der Walt and G. Mitchell
Department of Physiology, Faculty of Veterinary Science, University of Pretoria, Republic of South Africa.
This study set out to investigate tolerance of the body water pool to
short-term water deprivation in horses and, in particular, to assess
whether feral horses from the Namib Desert showed tolerance to dehydration
superior to Transvaal. Hydration status was compared in six feral horses
from the Namib Desert and in six Boerperd farm horses under conditions of
normal hydration and after 72 h of dehydration. Under normal hydration, the
two groups did not differ significantly in water intake, plasma sodium and
potassium concentrations, plasma osmolality, hematocrit, total plasma
protein, body water content, or water turnover (ml.kg-0.82.day-1). The
Namib horses were significantly smaller (P less than 0.0001) and turned
over 5 liters less water per day than the Boerperd during normal hydration
and 4 liters less during dehydration. Increases in plasma sodium
concentration after 72 h of dehydration were greater (P less than 0.05) in
the Namib horses. It was concluded that horses can easily tolerate water
deprivation that results in a 12% reductions in body mass. The feral horses
of the Namib desert were not significantly different per unit mass from
domestic horses with regard to indexes of total body water content under
conditions of normal hydration and after 72 h of dehydration. Their smaller
size and, hence, lower water turnover might be mechanisms they use for
survival in the Namib Desert.
