The effect of feeding frequency and voluntary sodium intake (VSI) on fluid shifts and plasma aldosterone concentration (PAC) were studied at rest and after exercise in six athletic horses. The horses were fed twice a day (2TD) and six times a day (6TD) for 25 days for each protocol, according to a changeover design. VSI was measured by weighing each horse's salt block daily. Feeding 2TD or 6TD caused no major alterations in fluid shifts, but in the 2TD treatment there was a postprandial increase in plasma protein concentration and osmolality that lasted <1 h. PAC and VSI were not affected by feeding frequency. VSI ranged from 0 to 62 mg · kg body weight¹ · day¹ and caused significant alterations in PAC. At VSI <26 mg · kg body weight¹ · day¹, a diurnal rhythm for PAC was noted. Water intake, fecal concentrations of sodium and potassium, and packed cell volume during exercise were influenced by VSI. The response to exercise did not differ between treatments. In conclusion, VSI, but not feeding frequency, has significant effects on fluid and electrolyte regulation in athletic horses.

aldosterone; exercise; feces; fluid balance; sodium deficiency

This article has been cited by other articles:

				A. P. Waller, G. J. F. Heigenhauser, R. J. Geor, L. L. Spriet, and M. I. Lindinger Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances muscle glycogen resynthesis in Standardbred horses J Appl Physiol, January 1, 2009; 106(1): 91 - 100. [Abstract] [Full Text] [PDF]

				A. Jansson, A. Lindholm, and K. Dahlborn Effects of acute intravenous aldosterone administration on Na+, K+, and water excretion in the horse J Appl Physiol, January 1, 2002; 92(1): 135 - 141. [Abstract] [Full Text] [PDF]