Weight loss, water loss and cation balance during the endurance test of a 3‐day event

Abstract

Summary Bodyweights (BW) of 39 horses, competing in a 3‐day event, were measured the evening before the endurance test (BW 1 ), after phase D (BW 2 ) and the next morning before stadium jumping (BW 3 ). Plasma sodium concentration [Na 1 ] was measured the evening before and after phase C of the endurance test [Na 2 ]. Total body water (TBW 1 ) was calculated using the formula (BW1 (kg) × 0.66 l/kg) and water loss (WL) was calculated as [(BW 1 – BW x ) X 0.9]. Cation balance (CB), the exchangeable cation concentration, was calculated using the formula [(TBW 1 (1) X Na 1 ) ‐ (TBW 2 (1)] X Na 2 ). The decrease in BW and TBW averaged 17.4 ± 1.0 kg and 15.6 ± 0.8 litres respectively (mean ± s.e.m.) during the endurance test and remained decreased 9.2 ± 1.0 kg (BW) and 8.3 ± 1.0 litres (TBW) for 18 to 24 h after competition. Plasma sodium concentration after phase C of the endurance test (141.2 ± 0.3 mmol/l) was greater than resting values (138.8 ± 0.2 mmol/l), resulting in a net decrease in CB (‐1601.1 ± 171.7 mmol). Significant water and electrolyte losses occur in horses competing in the endurance test of a 3‐day event and these fluid losses persist for 18–24 h after this phase of competition.