Adaptations to daily exercise in hot and humid ambient conditions in trained thoroughbred horses.
Abstract: The objectives of this study were to: 1) determine the effects of heat and high relative humidity (RH) on the clinical and physiological responses of horses during and after daily exercise training and 2) determine whether repeated exposure to, and exercise in, the heat would result in improved thermal tolerance (heat acclimation). Six trained Thoroughbred horses completed 1 h of submaximal exercise in cool, dry conditions (CD) and during a daily 4 h period of exposure to high heat and humidity (HH, room temperature = 33-35 degrees C, RH = 80-85%) for 22 days. Rectal temperature (Tre) and heart rate (HR) were measured before, during and after exercise and respiratory rate (RR) was measured before exercise and during a 2 h recovery. In HH, the rate of rise in Tre was significantly higher than in CD. However, by HH Day 5, Tre before, during and after exercise was significantly lower than on HH Day 1. The day-to-day decrease in Tre during exercise was reflected in significant decreases in heat storage following exercise by HH Day 10 (910 +/- 47 kcal) when compared to HH Day 1 (1211 +/- 75 kcal). At rest, RR was initially higher in HH than CD, and a further increase in pre-exercise RR from HH Day 1 to Day 10 may have contributed to the lower pre-exercise Tre. Recovery RR was higher after HH Day 1 and was associated with a lower end-of-exercise HR did not change in the 1 h before exercise in CD and did not differ from HH Days 1-22. By HH Day 10, mean HR during the latter part of exercise was lower than HH Day 1 and was not different from pre-exercise by 60 min of recovery. Pre-exercise body mass did not change during the 3 wk period and the decrease in body mass that occurred during the 4 h training period was significantly attenuated by HH Day 15 (9.8 +/- 0.8 kg) when compared to HH Day 1 (12.5 +/- 0.8 kg). Over the 3 week period of HH, mean 24 h water consumption increased from 26.0 +/- 2.1 litres to 39.5 +/- 3.2 litres, largely reflecting a 2-fold increase in water intake during the 4 h period of heat exposure. It is concluded that 3 weeks of daily exposure to, and exercise in, hot and humid ambient conditions resulted in a progressive reduction in thermal and cardiovascular strain. Furthermore, the reported physiological adaptations are consistent with an improved thermal tolerance (heat acclimation).
Publication Date: 1996-07-01 PubMed ID: 8894552DOI: 10.1111/j.2042-3306.1996.tb05033.xGoogle Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research examined the effects of high heat and humidity conditions on trained thoroughbred horses during and after daily exercise over a 22-day period. The study found an improved thermal and cardiovascular tolerance in horses, which can be attributed to their adaptation to these conditions over time.
Study Objectives and Methodology
- The study aimed to assess how heat and high relative humidity (RH) influences the clinical and physiological responses of horses during and after daily exercise training. It also sought to understand if repeated exposure to heat during exercise could result in increased heat tolerance or heat acclimation.
- Six trained Thoroughbred horses underwent a series of tests for 22 days, involving 1 hour of submaximal exercise in cool, dry conditions and during a 4-hour period in high heat and humidity (33-35 degrees C, 80-85% RH).
- Content measurements like rectal temperature (Tre), heart rate (HR), and respiratory rate (RR) were taken before, during, and after the exercise period. The RR was measured additionally during a 2-hour recovery period.
Key Findings
- The rate of increase in rectal temperature was higher in high heat humidity conditions, although it started to decrease significantly after the fifth day.
- The decrease in temperature was reflected in a significant decline in heat storage after exercise by day 10.
- The study observed high respiratory rates (RR) during high heat conditions, leading to decreased pre-exercise temperatures by day 10.
- The end-of-exercise heart rate was lower and didn’t change in the 1-hour before exercise, and didn’t differ significantly in high heat conditions. By day 10, the mean heart rate during the latter part of the exercise was lower than on day 1.
- Body mass did not change significantly during the 3-week period, though the decrease that occurred during the 4-hour training period was significantly less by day 15.
- Over the study period, water consumption increased largely due to a two-fold increase in water intake during the heat exposure period.
Summary of Study
- The study concluded that 3 weeks of daily exposure to, and exercise in, hot and humid ambient conditions resulted in a progressive reduction in thermal and cardiovascular strain. It suggests that the physiological adaptations observed in the horses are consistent with improved thermal tolerance or heat acclimation.
Cite This Article
APA
Geor RJ, McCutcheon LJ, Lindinger MI.
(1996).
Adaptations to daily exercise in hot and humid ambient conditions in trained thoroughbred horses.
Equine Vet J Suppl(22), 63-68.
https://doi.org/10.1111/j.2042-3306.1996.tb05033.x Publication
Researcher Affiliations
- Department of Clinical Studies, Ontario Veterinary College, Canada.
MeSH Terms
- Adaptation, Physiological
- Animals
- Body Temperature
- Body Temperature Regulation
- Body Weight / physiology
- Drinking / physiology
- Exercise Test / veterinary
- Heart Rate
- Horses / physiology
- Hot Temperature
- Humidity
- Osmolar Concentration
- Oxygen Consumption
- Physical Conditioning, Animal / physiology
- Respiration / physiology
Citations
This article has been cited 7 times.- Ebisuda Y, Mukai K, Takahashi Y, Yoshida T, Kawano A, Matsuhashi T, Miyata H, Kuwahara M, Ohmura H. Acute exercise in a hot environment increases heat shock protein 70 and peroxisome proliferator-activated receptor γ coactivator 1α mRNA in Thoroughbred horse skeletal muscle. Front Vet Sci 2023;10:1230212.
- Kang H, Zsoldos RR, Sole-Guitart A, Narayan E, Cawdell-Smith AJ, Gaughan JB. Heat stress in horses: a literature review. Int J Biometeorol 2023 Jun;67(6):957-973.
- Trigg LE, Lyons S, Mullan S. Risk factors for, and prediction of, exertional heat illness in Thoroughbred racehorses at British racecourses. Sci Rep 2023 Mar 14;13(1):3063.
- Harvey AM, Ramp D, Mellor DJ. Review of the Foundational Knowledge Required for Assessing Horse Welfare. Animals (Basel) 2022 Dec 1;12(23).
- Lindinger MI, Waller AP. Physicochemical Analysis of Mixed Venous and Arterial Blood Acid-Base State in Horses at Core Temperature during and after Moderate-Intensity Exercise. Animals (Basel) 2022 Jul 22;12(15).
- Ebisuda Y, Mukai K, Takahashi Y, Yoshida T, Matsuhashi T, Kawano A, Miyata H, Kuwahara M, Ohmura H. Heat acclimation improves exercise performance in hot conditions and increases heat shock protein 70 and 90 of skeletal muscles in Thoroughbred horses. Physiol Rep 2024 May;12(10):e16083.
- Munsters C, Siegers E, Sloet van Oldruitenborgh-Oosterbaan M. Effect of a 14-Day Period of Heat Acclimation on Horses Using Heated Indoor Arenas in Preparation for Tokyo Olympic Games. Animals (Basel) 2024 Feb 6;14(4).
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