Adaptations of White-Tailed Deer to Naturally Occurring Sodium Deficiencies

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Abstract
Investigations of seasonally occurring salt drive in a S Indiana [USA] white-tailed deer (Odocoileus virginianus) population revealed low environmental Na levels and several physiological, morphological and behavioral adaptations in deer to counter Na deficiency. Na levels in soils, water and food plants were generally low. Monthly Na intake via food in deer ranged from 35 ppm in Sept. to 103 ppm in Feb., far below that recommended for livestock. Natural mineral licks, which averaged 382 ppm Na, were used heavily by deer in April and May, but no use occurred in winter months. The percentage of adrenal cortex occupied by zona glomerulosa tissue was significantly larger in spring than summer or fall, indicating increased mineralocorticoid production. Urine Na levels in spring and summer indicated large resorptive capacity by the kidney; however, substantial quantities of Na occasionally were lost in urine, as well as feces. Behavioral and physiological mechanisms in deer appear sufficiently well-developed to allow maintenance of a positive Na balance under most circumstances. The intense Na drive in spring correlated closely with peak obligatory intake of K and H2O in food. A mechanism is postulated whereby high intake of K and H2O leads to excessive Na loss and a temporary negative Na balance.