Sweat composition in Arabian horses performing endurance exercise on forage-based, low Na rations



Reasons for performing study: Excessive sweat loss during endurance exercise may lead to electrolyte disturbances and previous research suggests dietary factors may affect hydration status. While investigating the effect of dietary fibre type on hydration status, sweat samples were collected which allowed for the evaluation of sweat composition in horses consuming forage-based, low sodium (Na) rations.

Objective: To investigate sweat composition in Arabian horses performing endurance type exercise while fed forage-based, rations low in Na.

Methods: Six 2-year-old Arabian horses were fed, according to a replicated 3 × 3 Latin square, either grass hay (G), 50:50 grass hay:alfalfa hay (GA), or 50:50 grass hay: chopped fibres (GM) without any additional electrolyte supplementation. After 14 days on each diet, horses performed a 60 km treadmill exercise test. Sweat was collected from sealed pouches on the dorsal thorax after each of four 15 km exercise bouts.

Results: Intake (g/day) of Na (2.5 ± 0.4), Cl (72 ± 16), and Mg (18 ± 3) were not different between diets but K and Ca intakes (g/day) were greater (P<0.05) on GA (246 ± 35; 101 ± 14) than G (176 ± 38; 59 ± 14) or GM (168 ± 33; 62 ± 15). There was no effect of diet on sweat pH (7.65 ± 0.04) or concentrations (mmol/l) of K (46 ± 3), Cl (133 ± 7), Ca (8.5 ± 1.1), or Mg (2.3 ± 0.3); yet diet did influence sweat Na concentration (P<0.05, G 88 ± 5 mmol/l, GA 104 ± 5, GM 96 ± 6). Na and Cl concentrations were lower than those previously reported.

Conclusions: Differences in sweat constituents due to diet were observed, but more importantly both Na and Cl concentration are lower than those previously reported perhaps due to low dietary Na intake or breed of animal.