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Animals : an open access journal from MDPI2020; 10(4); doi: 10.3390/ani10040572

Mouth Pain in Horses: Physiological Foundations, Behavioural Indices, Welfare Implications, and a Suggested Solution.

Abstract: A proposition addressed here is that, although bitted horses are viewed by many equestrians as being largely free of bit-related mouth pain, it seems likely that most behavioural signs of such pain are simply not recognised. Background information is provided on the following: the major features of pain generation and experience; cerebrocortical involvement in the conscious experience of pain by mammals; the numerous other subjective experiences mammals can have; adjunct physiological responses to pain; some general feature of behavioural responses to pain; and the neural bases of sensations generated within the mouth. Mouth pain in horses is then discussed. The areas considered exclude dental disease, but they include the stimulation of pain receptors by bits in the interdental space, the tongue, the commissures of the mouth, and the buccal mucosa. Compression, laceration, inflammation, impeded tissue blood flow, and tissue stretching are evaluated as noxious stimuli. The high pain sensitivity of the interdental space is described, as are likely increases in pain sensitivity due to repeated bit contact with bruises, cuts, tears, and/or ulcers wherever they are located in the mouth. Behavioural indices of mouth pain are then identified by contrasting the behaviours of horses when wearing bitted bridles, when changed from bitted to bit-free bridles, and when free-roaming unbitted in the wild. Observed indicative behaviours involve mouth movements, head-neck position, and facial expression ("pain face"), as well as characteristic body movements and gait. The welfare impacts of bit-related pain include the noxiousness of the pain itself as well as likely anxiety when anticipating the pain and fear whilst experiencing it, especially if the pain is severe. In addition, particular mouth behaviours impede airflow within the air passages of the upper respiratory system, effects that, in their turn, adversely affect the air passages in the lungs. Here, they increase airflow resistance and decrease alveolar gas exchange, giving rise to suffocating experiences of breathlessness. In addition, breathlessness is a likely consequence of the low jowl angles commonly maintained during dressage. If severe, as with pain, the prospect of breathlessness is likely to give rise to anxiety and the direct experience of breathlessness to fear. The related components of welfare compromise therefore likely involve pain, breathlessness, anxiety, and fear. Finally, a 12-point strategy is proposed to give greater impetus to a wider adoption of bit-free bridles in order to avoid bit-induced mouth pain.
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Publication Date: 2020-03-29 PubMed ID: 32235343PubMed Central: PMC7222381DOI: 10.3390/ani10040572Google Scholar: Lookup
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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.

This research article investigates the occurrence of mouth pain in horses due to the usage of bits and suggests a change in bridle types to reduce bit-related mouth pain. The study closely examines the horses’ behaviours, seeking to validate that unrecognized signs of pain are likely shown by horses wearing traditional bitted bridles.

The Concept of Pain in Horses

  • The paper begins by detailing certain tenets of pain generation and experience, including how mammals consciously perceive pain and any associated physiological responses. This exploration lays the foundation for the subsequent discussion on horses’ mouth pain.
  • The focus is on the pain resulting from non-dental causes, particularly the use of bits that stimulate pain receptors located in the interdental space, the tongue, the mouth’s corners (commissures), and the cheek lining (buccal mucosa).

Sources of Mouth Pain

  • The primary causes of such pain are examined, including compression, laceration, inflammation, restricted blood flow, and tissue stretching, recognizing them as harmful stimuli.
  • Increased sensitivity in the interdental space is discussed, along with the likelihood of increased pain sensitivity due to repeated bit contact with mouth wounds, which elevates the level of distress.

Behavioural Indicators of Pain

  • To identify signs of mouth pain, the study contrasts behaviours between horses wearing bitted bridles, bit-free bridles, and horses roaming freely in the wild.
  • Revealing indicators include mouth movements, head-neck positions, “pain face” expressions, and changes in body movement and gait.

Welfare Impacts of Bit-Related Pain

  • The direct pain and psychological suffering horses experience due to bit-related mouth pain are evaluated. Apart from the distressing pain, horses likely feel anxious when anticipating the pain and fear when experiencing it.
  • It was observed that bit-induced mouth behaviours hinder airflow in the horse’s upper respiratory system, causing resistance and reduced gas exchange in the lungs that lead to breathlessness. This breathlessness can also be a result of the horse maintaining low jowl angles for dressage.
  • Thus, the overall welfare compromise discussed in the study revolves around these four aspects – pain, breathlessness, anxiety, and fear.

Suggested Solution

  • Finally, a strategy comprising of 12 points is proposed, aiming towards encouraging the broader adoption of bit-free bridles as a solution to avoid the mouth pain caused by conventional bitts.

Cite This Article

APA
Mellor DJ. (2020). Mouth Pain in Horses: Physiological Foundations, Behavioural Indices, Welfare Implications, and a Suggested Solution. Animals (Basel), 10(4). https://doi.org/10.3390/ani10040572

Publication

Animals : an open access journal from MDPI
ISSN: 2076-2615
NlmUniqueID: 101635614
Country: Switzerland
Language: English
Volume: 10
Issue: 4

Researcher Affiliations

Mellor, David J
  • Animal Welfare Science and Bioethics Centre, School of Veterinary Science, Massey University, Palmerston North 4474, New Zealand.

Conflict of Interest Statement

The author declares no conflict of interest.

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