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

This research is primarily a comparison between dehydrated horses and those that are properly hydrated, with the aim of investigating the impacts of dehydration on a horse’s ability to perform physically demanding tasks, like pulling heavy weights.

Introduction

• The research focused on a group of 43 Valencian draft horses which were purposely dehydrated by withholding food and water, and a group of 11 euhydrated (properly hydrated) horses.
• These horses were subjected to physically demanding tasks involving pulling weights, and various health indicators and physiological responses were monitored both during and after the exercises.

Experimental Setup and Groupings

• The horses in both groups were classified into three categories based on bodyweight: Category A consisted of horses weighing 350 kg or less, Category B included horses between 351-450 kg, and Category C included the heavier horses weighing 451 kg and above.
• The weight each horse had to pull was determined according to its bodyweight category: those in Category A pulled twice their bodyweight, while those in Category B and C pulled 2.25 and 2.5 times their bodyweight respectively. Exercise duration averaged at 1.3 minutes.

Measurements Taken

• Various physiological parameters were measured in both groups of horses at rest, during exercise, and for the first 30 minutes of recuperation after exercise.
• These measurements included heart rate, respiratory rate, rectal temperature and blood work to assess health indicators, among which the primary focus was on arginine vasopressin level, a hormone that regulates water balance in the body.

Results and Findings

• The only significant difference observed between the bodyweight categories was the packed cell volume (PCV), which was higher in the dehydrated horses in Category A compared to Category B after exercise.
• As a result of this finding, the data for all three bodyweight categories was combined for further analysis.
• Horses in the dehydrated group had higher resting levels of plasma proteins, albumin, urea, creatinine, sodium, and arginine vasopressin compared to the euhydrated group. Albumin, urea, and plasma protein levels are indicators of hydration status, while creatinine is a marker of kidney function.
• The dehydrated horses also exhibited greater increases in heart rate and lactate levels during exercise, suggesting greater physical strain on these animals. Lactate buildup in muscles is a sign of oxygen debt and physiological stress.
• The study found a negative correlation between exercise duration and arginine vasopressin, implying a connection between hydration status and the animal’s ability to sustain physically demanding activities.
• Interestingly, peak concentrations of the arginine vasopressin hormone did not differ between the two groups.