Effects of dehydration on thermoregulatory responses of horses during low-intensity exercise.
Abstract: Effects of dehydration on thermoregulatory and metabolic responses were studied in six horses during 40 min of exercise eliciting approximately 40% of maximal O2 consumption and for 30 min after exercise. Horses were exercised while euhydrated (C), 4 h after administration of furosemide (FDH; 1.0 mg/kg i.v.) to induce isotonic dehydration, and after 30 h without water (DDH) to induce hypertonic dehydration. Cardiac output was significantly lower in FDH (144.1 +/- 8.0 l/min) and in DDH (156.6 +/- 6.9 l/min) than in C (173.1 +/- 6.2 l/min) after 30 min of exercise. When DDH, FDH, and C values were compared, dehydration resulted in higher temperatures in the middle gluteal muscle (41.9 +/- 0.3, 41.1 +/- 0.2, and 40.6 +/- 0.2 degrees C, respectively) and pulmonary artery (40.8 +/- 0.3, 40.1 +/- 0.2, and 39.7 +/- 0.2 degrees C, respectively). Temperatures in the superficial thoracic vein and subcutaneous sites on the neck and back and peak sweating rates on the neck and back were not significantly different in DDH and C. In view of higher core temperatures during exercise after dehydration and decrease in cardiac output without concomitant increases in peripheral temperatures or reduced sweating rates, we conclude that the impairment of thermoregulation was primarily due to decreased transfer of heat from core to periphery.
Publication Date: 1993-08-01 PubMed ID: 8226506DOI: 10.1152/jappl.1993.75.2.994Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research investigated how dehydration affects thermoregulatory and metabolic responses in horses. Specifically, the study examined the effects during low intensity exercise and post-exercise recovery, and found that dehydration led to lower cardiac output, increased core temperatures, and decreased heat transfer from core to body surface.
Experimental Design
- The study involved six horses, which were put through exercise and recovery sessions under three conditions: normal hydration (C), isotonic dehydration induced by furosemide injection (FDH), and hypertonic dehydration caused by withholding water for 30 hours (DDH).
- The exercise was low-intensity, designed to prompt around 40% of maximum O2 consumption and lasted for approximately 40 minutes. Recovery time was monitored for 30 minutes following exercise.
Outcomes
- The research found that cardiac output, or the volume of blood the heart pumps per minute, was significantly lower when the horses were dehydrated (both FDH and DDH) compared to when they were at a normal hydration state.
- Core temperatures, measured in the middle gluteal muscle and the pulmonary artery, were higher when the horses were dehydrated (again, both FDH and DDH) than when they were normally hydrated. Moreover, there was no notable difference in the temperatures in the superficial thoracic vein and the subcutaneous sites on the back and neck or in peak sweating rates between dehydrated and normal states.
Conclusion
- Based on these findings, the study concluded that dehydration impairs the thermoregulatory system of horses, raising core temperatures and reducing the transfer of heat from the core to the periphery, i.e., body surface. This decrease in heat transfer, rather than a decrease in peripheral temperatures or reduced sweating rates, appears to explain the elevated core temperatures observed.
Implications
- The research carries important implications for the care of exercising horses. Hydration should be carefully managed to prevent impaired thermoregulation and negative impacts on the horse’s performance and wellbeing.
Cite This Article
APA
Naylor JR, Bayly WM, Gollnick PD, Brengelmann GL, Hodgson DR.
(1993).
Effects of dehydration on thermoregulatory responses of horses during low-intensity exercise.
J Appl Physiol (1985), 75(2), 994-1001.
https://doi.org/10.1152/jappl.1993.75.2.994 Publication
Researcher Affiliations
- Department of Veterinary Clinical Medicine and Surgery, College of Veterinary Medicine, Washington State University, Pullman 99164.
MeSH Terms
- Animals
- Body Temperature Regulation / physiology
- Body Weight / physiology
- Cardiac Output / physiology
- Dehydration / physiopathology
- Female
- Furosemide / pharmacology
- Heart Rate / physiology
- Hemodynamics / drug effects
- Hemodynamics / physiology
- Horses / physiology
- Male
- Muscles / drug effects
- Muscles / physiology
- Oxygen Consumption / drug effects
- Oxygen Consumption / physiology
- Physical Exertion / physiology
- Sweating / physiology
- Water Deprivation / physiology
Citations
This article has been cited 2 times.- Lindinger MI. Oral Electrolyte and Water Supplementation in Horses. Vet Sci 2022 Nov 10;9(11).
- Tennent-Brown BS, Goetz TE, Manohar M, Hassan AS, Freeman DE, Bundy JS, Evans MR. Hyperhydration prior to a simulated second day of the 3-day moderate intensity equestrian competition does not cause arterial hypoxemia in Thoroughbred horses. Eur J Appl Physiol 2006 Jul;97(4):462-70.
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