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Home / Equine Research Bank / Biol Lett / Guttural pouches, brain temperature and exercise in horses.
Biology letters2006; 2(3); 475-477; doi: 10.1098/rsbl.2006.0469

Guttural pouches, brain temperature and exercise in horses.

Abstract: Selective brain cooling (SBC) is defined as the lowering of brain temperature below arterial blood temperature. Artiodactyls employ a carotid rete, an anatomical heat exchanger, to cool arterial blood shortly before it enters the brain. The survival advantage of this anatomy traditionally is believed to be a protection of brain tissue from heat injury, especially during exercise. Perissodactyls such as horses do not possess a carotid rete, and it has been proposed that their guttural pouches serve the heat-exchange function of the carotid rete by cooling the blood that traverses them, thus protecting the brain from heat injury. We have tested this proposal by measuring brain and carotid artery temperature simultaneously in free-living horses. We found that despite evidence of cranial cooling, brain temperature increased by about 2.5 degrees C during exercise, and consistently exceeded carotid temperature by 0.2-0.5 degrees C. We conclude that cerebral blood flow removes heat from the brain by convection, but since SBC does not occur in horses, the guttural pouches are not surrogate carotid retes.
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Publication Date: 2006-12-07 PubMed ID: 17148434PubMed Central: PMC1686210DOI: 10.1098/rsbl.2006.0469Google Scholar: Lookup
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  • Non-U.S. Gov't

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The study explores the role of guttural pouches in horses as a potential mechanism for selective brain cooling (SBC) during physical activity. The study concludes that despite initial hypotheses, these guttural pouches do not function similarly to the carotid rete in other species and SBC does not occur in horses.

Understanding of the Study

  • The study aims to understand the mechanism behind temperature regulation in the brain of horses, specifically during exercise. It investigates if the guttural pouches in horses serve the same function as a carotid rete, an anatomical structure that cools arterial blood before it enters the brain in artiodactyls (a group to which horses do not belong).
  • The survival function of this cooling mechanism is to protect the brain tissue from damage due to heat, especially during exercise.

Results of the Study

  • To test this hypothesis, the researchers measured the temperature of the brain and the carotid artery in freely living horses. They found that while there was some cooling in the cranial area, the brain temperature still increased by roughly 2.5 degrees Celsius during exercise.
  • Additionally, the brain temperature was consistently 0.2-0.5 degrees Celsius higher than the temperature of the carotid artery. This indicates that the guttural pouches do not cool the blood in the same way a carotid rete does in a situation of physical exertion.

Conclusion of the Study

  • Even though it was observed that during exercise there is some level of cranial cooling, the conclusion drawn from the study findings is that SBC does not occur in horses. Thus, the guttural pouches in horses do not serve as surrogate carotid retes, an initial hypothesis of the study.
  • The difference in the temperature of the brain and carotid artery indicates that the heat from the brain is removed via cerebral blood flow by convention, rather than selective cooling via the guttural pouches.

Implications of the Study

  • This research has implications on our understanding of heat management in horse physiology, especially during exercise. It brings clarity to the question of how perissodactyls (horse family) manage brain temperature during physical exertion compared to other animal groups.
  • The findings will be integral for future research understanding brain function and temperature management in other species and could contribute to better practices in sporting and working horses.

Cite This Article

APA
Mitchell G, Fuller A, Maloney SK, Rump N, Mitchell D. (2006). Guttural pouches, brain temperature and exercise in horses. Biol Lett, 2(3), 475-477. https://doi.org/10.1098/rsbl.2006.0469

Publication

Biology letters
ISSN: 1744-9561
NlmUniqueID: 101247722
Country: England
Language: English
Volume: 2
Issue: 3
Pages: 475-477

Researcher Affiliations

Mitchell, Graham
  • School of Physiology, University of the Witwatersrand Medical School, 7 York Road, Parktown 2193, Johannesburg, South Africa. mitchg@uwyo.edu
Fuller, Andrea
    Maloney, Shane K
      Rump, Nicola
        Mitchell, Duncan

          MeSH Terms

          • Animals
          • Body Temperature Regulation / physiology
          • Brain / physiology
          • Cerebrovascular Circulation / physiology
          • Diverticulum / veterinary
          • Eustachian Tube / anatomy & histology
          • Eustachian Tube / physiology
          • Horses / anatomy & histology
          • Horses / physiology
          • Mammals
          • Physical Exertion / physiology
          • Species Specificity

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          Citations

          This article has been cited 9 times.
          1. 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.
            doi: 10.1007/s00484-023-02467-7pubmed: 37060454google scholar: lookup
          2. Brownlow M, Mizzi JX. An Overview of Exertional Heat Illness in Thoroughbred Racehorses: Pathophysiology, Diagnosis, and Treatment Rationale.. Animals (Basel) 2023 Feb 9;13(4).
            doi: 10.3390/ani13040610pubmed: 36830397google scholar: lookup
          3. 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).
            doi: 10.3390/ani12151875pubmed: 35892525google scholar: lookup
          4. Verdegaal EJMM, Howarth GS, McWhorter TJ, Delesalle CJG. Is Continuous Monitoring of Skin Surface Temperature a Reliable Proxy to Assess the Thermoregulatory Response in Endurance Horses During Field Exercise?. Front Vet Sci 2022;9:894146.
            doi: 10.3389/fvets.2022.894146pubmed: 35711810google scholar: lookup
          5. Verdegaal EJMM, Howarth GS, McWhorter TJ, Boshuizen B, Franklin SH, Vidal Moreno de Vega C, Jonas SE, Folwell LE, Delesalle CJG. Continuous Monitoring of the Thermoregulatory Response in Endurance Horses and Trotter Horses During Field Exercise: Baselining for Future Hot Weather Studies.. Front Physiol 2021;12:708737.
            doi: 10.3389/fphys.2021.708737pubmed: 34512382google scholar: lookup
          6. Wang H, Wang B, Normoyle KP, Jackson K, Spitler K, Sharrock MF, Miller CM, Best C, Llano D, Du R. Brain temperature and its fundamental properties: a review for clinical neuroscientists.. Front Neurosci 2014;8:307.
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            doi: 10.1007/s00360-009-0352-6pubmed: 19277681google scholar: lookup
          8. Maloney SK, Fuller A, Meyer LC, Kamerman PR, Mitchell G, Mitchell D. Brain thermal inertia, but no evidence for selective brain cooling, in free-ranging western grey kangaroos (Macropus fuliginosus).. J Comp Physiol B 2009 Apr;179(3):241-51.
            doi: 10.1007/s00360-008-0308-2pubmed: 18820935google scholar: lookup
          9. Mitchell G, Lust A. The carotid rete and artiodactyl success.. Biol Lett 2008 Aug 23;4(4):415-8.
            doi: 10.1098/rsbl.2008.0138pubmed: 18426746google scholar: lookup
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