WEIGHT, WATER, AND CATION LOSSES IN HORSES COMPETING IN A 3-DAY EVENT

Body weight of 48 horses competing in a 3-day event was measured the d ay before the event (baseline), following the dressage phase of the ev ent (day 1), after the endurance phases of the event (day 2), and 18 t o 24 hours after the endurance phases (day 3). Plasma sodium and potas sium concentrations were measured the evening before, immediately afte r, and 10 minutes after the endurance phases. Total body water, water loss, and net exchangeable cation loss were then calculated. Body weig ht and total body water were significantly decreased, compared with ba seline values, at all times during the event, and significant water lo ss was detected. The largest changes were recorded after the endurance phases of the event. Water deficits were still detected 18 to 24 hour s after the endurance phases of the event. Mean plasma sodium concentr ation was significantly increased immediately after the endurance phas es of the event, compared with concentration measured the evening befo re, and remained increased after the 10-minute recovery period, presum ably because of dehydration. Mean plasma potassium concentration was s ignificantly increased immediately after the endurance phases of the e vent, compared with concentration measured the evening before, but was not increased after the 10-minute recovery period.