Abstract
The provision of NaCl, according to current recommendations, to horses in moderate work has been shown to induce immediate postprandial acidosis. The present study aimed to clarify whether this NaCl induced acidosis i) persists beyond the immediate postprandial period, and ii) is still present after a 2 week adaptation period. Six adult warmblood mares in moderate work received daily 1.00 kg hay per 100 kg body weight (bwt) only together with 0.64 kg unprocessed cereal grains/100 kg bwt.d as fed basis. Using a 3x3 Latin Square, either 0 (NaCl-0), 50 (NaCl-50) or 100 (NaCl-100) g NaCl/d were fed together with the concentrates in two equal doses for 3 weeks. During the final week, a mineral digestibility trial was undertaken. The middle sodium and chloride intake (NaCl-50) at least met the most common recommendations for moderate work. Morning (7:00 AM) urine and venous blood samples were collected on days 0, 1–4, 8, and 15, and analysed for pH, acid-base status, creatinine and electrolyte concentrations. Fractional electrolyte clearances (FC) were determined. Mean apparent sodium digestibility ranged between 60–62% whereas chloride digestibility was consistently above 94%. Supplementing 100 g but not 50 g of NaCl resulted in significant reduction of blood pH and base excess as well as urinary pH and urine acid excretion. Both 50 g and 100 g NaCl supplementation caused a significant reduction in base and net acid-base excretion, urine density and potassium concentration, but increased urine sodium concentration and the FC of sodium and chloride (P < 0.05). This suggests that a high proportion of the recommended salt doses is excreted renally. The above effects of NaCl supplementation persisted over the 2 week measurement period. Results suggest that feeding 100 g NaCl to moderately exercising horses results in mild metabolic acidosis, whereas feeding 50 g according to current recommendations resulted in compensated acidosis.
Highlights
The level of sodium and chloride in typical horse forages and feeds is low [1]
He stated that ‘no matter how necessary sodium may be for herbivore in the wild state it is perfectly certain that under domestication they can be maintained in perfect health without receiving any more than is normally contained in their food.’
The addition of 100 g of NaCl to a 60:40 hay:concentrate diet, with adequate intakes of calcium, magnesium and phosphorus, fed to horses in moderate work resulted in a mild metabolic acidosis. 50 g of NaCl supplementation under the same conditions appeared to result in a compensated metabolic acidosis as the urine and blood pH were not significantly affected
Summary
The level of sodium and chloride in typical horse forages and feeds (especially non-commercially manufactured) is low [1]. On the other hand, eventing horses receiving no or ‘inadequate’ amounts of additional NaCl supplementation showed persistent good performance and apparently undisturbed health [13]. Back in 1890, Smith [15] reported that horses working without any additional salt intake retained apparent excellent health. He stated that ‘no matter how necessary sodium may be for herbivore in the wild state (as travellers would have us believed) it is perfectly certain that under domestication they can be maintained in perfect health without receiving any more than is normally contained in their food.’
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