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Home / Equine Research Bank / Physiol Rep / Muscular tension as an indicator of acute stress in horses.
Physiological reports2022; 10(6); e15220; doi: 10.14814/phy2.15220

Muscular tension as an indicator of acute stress in horses.

Abstract: Horses' muscular tension during acute stress remains unexplored. Our aim was to assess muscular, behavioral, cortisol, and hematocrit responses to social isolation (ISO), novel object exposure (NOV), and sham clipping (CLIP). Altered stress responses were expected. Eight mature Standardbred horses (four mares and four geldings) were exposed to acute stressors and a control period (CON) in a balanced, replicated 4×4 Latin Square experimental design with 3 min treatment periods and 10 min washout periods. Surface electromyography collected from the masseter, brachiocephalas, cervical trapezius, and longissimus dorsi was processed to derive average rectified value (ARV) and median frequency (MF) during the initial, middle, and final 30 s of treatments. ARV and MF data were log transformed then analyzed using a mixed model, repeated measures ANOVA along with plasma cortisol and hematocrit. Behavior data were analyzed using a negative binomial distribution mixed model ANOVA. CLIP resulted in greater (p < 0.05) log ARV in the masseter (1.5 + 1.5%, mean + SD) and brachiocepahlas (2.2 + 2.0%) than CON (-1.2 + 1.4%, 0.1 + 1.5%). ISO resulted in greater (p < 0.05) log ARV in the masseter (0.2 + 1.3%) and cervical trapezius (0.6 + 1.3%) than CON (-1.2 + 1.4%, -1.0 + 1.7%). ISO increased (p < 0.05) the total number of stress-related behaviors and hematocrit. No changes in cortisol were observed. We suggest that muscular tension can be used as an indicator of acute stress in horses. Incorporating muscle activity into an array of measurements may provide a more nuanced understanding of stress responses.
© 2022 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.
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Publication Date: 2022-03-22 PubMed ID: 35307975PubMed Central: PMC8935158DOI: 10.14814/phy2.15220Google 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 investigates the link between muscular tension and acute stress in horses, examining their responses to different kinds of stressors. The study found that muscular tension can be a reliable indicator of acute stress in horses and it may provide a more nuanced understanding of stress responses.

Research Objectives and Methodology

  • The research aimed to study the muscular reactions of horses under acute stress, which was hitherto unexplored. This was done by studying muscular, behavioural, cortisol, and hematocrit (a measure of red blood cells in the blood) responses.
  • The acute stressors applied to the horses were social isolation (ISO), exposure to a new object (NOV), and sham clipping (CLIP). The reactions in each case were then compared with a control period (CON) where no stressors were applied.
  • The researchers employed a balanced, replicated 4×4 Latin Square experimental design. This involved eight mature Standardbred horses, with four male (geldings) and four female (mares). Each horse was subjected to the stressors, and each treatment lasted for 3 minutes, followed by a 10-minute rest period.
  • The muscle activity was measured using surface electromyography, focused on four key muscles. These readings were processed to calculate the average rectified value (ARV) and median frequency (MF) across the initial, middle, and final stages of each treatment.

Findings and Analysis

  • Sham clipping led to a significant increase in ARV in both the masseter and brachiocephalas muscles, indicating increased muscular tension.
  • Social isolation caused a similar increase in ARV in the masseter and cervical trapezius muscles, suggesting a similar rise in tension.
  • In contrast, the researchers discovered social isolation led to a rise in hematocrit and stress-related behaviour. This suggests that the stress of isolation affects more than just their muscular system but also leads to recognisable behaviours and a physiological response in terms of increased red blood cell count.
  • Despite the observable muscular and behavioural changes, no changes in cortisol (a common physiological stress marker) levels were observed under either stress condition.
  • Overall, the authors argue muscular tension, as measured by ARV, can be used as an indicator of acute stress in horses. They suggest incorporating muscle activity measurements into stress studies could provide a more detailed understanding of stress responses.

Cite This Article

APA
Rankins EM, Manso Filho HC, Malinowski K, McKeever KH. (2022). Muscular tension as an indicator of acute stress in horses. Physiol Rep, 10(6), e15220. https://doi.org/10.14814/phy2.15220

Publication

Physiological reports
ISSN: 2051-817X
NlmUniqueID: 101607800
Country: United States
Language: English
Volume: 10
Issue: 6
Pages: e15220

Researcher Affiliations

Rankins, Ellen M
  • Equine Science Center, Department of Animal Science, Rutgers The State University of New Jersey, New Brunswick, New Jersey, USA.
Manso Filho, Helio C
  • Departamento de Zootecnia, Universidade Federal Rural de Pernambuco (UFRPE), Recife-PE, Brasil.
Malinowski, Karyn
  • Equine Science Center, Department of Animal Science, Rutgers The State University of New Jersey, New Brunswick, New Jersey, USA.
McKeever, Kenneth H
  • Equine Science Center, Department of Animal Science, Rutgers The State University of New Jersey, New Brunswick, New Jersey, USA.

MeSH Terms

  • Animals
  • Electromyography
  • Female
  • Horses
  • Hydrocortisone
  • Male
  • Muscle Tonus

Conflict of Interest Statement

The authors have no conflict of interest to declare.

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