The effects of hypertonic dehydration changes on renal function and arginine vasopressin in the horse during pulling exercises.

This study investigated the effect of hypertonic dehydration on exercise in horses. Valencian draft horses (n=43) with hypertonic dehydration following water and food deprivation and competing in pulling events (COM), were compared to euhydrated horses (n=11) during a pulling exercise test (PET). Both groups were divided into bodyweight (BW) categories A (≤350 kg), B (351-450 kg), and C (≥451 kg), and pulled 2, 2.25, and 2.5 times BW, respectively. Exercise duration (ED) was 1.3±0.8 min. Heart rate, respiratory rate, rectal temperature and blood samples were taken at rest, after exercise, and during the first 30 min of passive recuperation. The only difference between BW categories was the packed cell volume (PCV), which was higher after exercise in COM horses in group A (52.7±2.3%) than in B (49.3±3.4%), so the data for the three BW categories were combined. The COM horses had higher levels of resting plasma proteins, albumin, urea, creatinine, sodium and arginine vasopressin (AVP) than PET horses. Exercise induced significantly greater (P<0.05) increases in heart rate and lactate in the COM horses. AVP was negatively correlated with ED and positively with PCV, plasma proteins, albumin, urea, and sodium. Peak AVP concentrations did not differ in the two groups.