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Frontiers in physiology2017; 8; 664; doi: 10.3389/fphys.2017.00664

Seasonal Variations in Heart Rate Variability as an Indicator of Stress in Free-Ranging Pregnant Przewalski’s Horses (E. ferus przewalskii) within the Hortobágy National Park in Hungary.

Abstract: Ecosystems with seasonal fluctuations in climate and food availability present physiological challenges to resident mammals and may cause "stress." The two predominant physiological responses to stressors are (1) the activation of the hypothalamic-pituitary-adrenal axis and (2) the modulation of the autonomic nervous system. To date, the primary indicator for "stress" in wildlife- and zoo animal research are glucocorticoid levels. By measuring the autonomic regulation of cardiac activity, particularly the vagal tone, heart rate variability (HRV) is presently emerging as a suitable indicator of "stress" in farm- and domestic animal research. The aim of this study was to use HRV, a novel method in wildlife research, to assess seasonal patterns of "stress" in a group of free-ranging Przewalski's horses (). Six pregnant Przewalski's horses from one harem within the Hortobágy National Park in Hungary were subjected to the study. We used a dedicated telemetry system consisting of a subcutaneously implanted transmitter and a receiver and storage unit in a collar to record HRV, heart rate (HR), subcutaneous body temperature, and activity throughout a one-year study period-climate data was also collected. We defined "stress" as a decrease in parasympathetic nervous system tone and calculated RMSSD (root mean square of successive differences) as a measure of HRV. Linear mixed effects models with random intercept per individual were used for statistical analysis. HRV and HR varied considerably throughout the year. Similar to temperate ruminants and hibernating mammals, Przewalski's horses experienced lower HR and HRV during winter, when resources are limited indicating decreased metabolic rates coupled with "stress." In spring, we observed a drop of HRV along with a peak in HR indicating an increase of allostatic load that is most likely associated with increased energy demands during pregnancy and/or seasonal routines such as the adjustment of the gastrointestinal system to better quality diet. Measuring telemetric HRV is a proven method to study undisturbed reactions of wild animals to their changing environment over the long term. Przewalski's horses experience a loss of complexity in cardiovascular dynamics over the winter and particularly during spring, indicating seasonal "stress."
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Publication Date: 2017-09-07 PubMed ID: 28936179PubMed Central: PMC5594093DOI: 10.3389/fphys.2017.00664Google 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.

The research focuses on understanding stress levels in Przewalski’s horses using heart rate variability (HRV) in relation to seasonal changes. Factors such as climate and metabolic rates, especially during winter and spring, were observed to influence the stress levels of six pregnant Przewalski’s horses in the Hortobágy National Park in Hungary.

Methodology

  • The study employed Heart Rate Variability (HRV) as a stress indicator, which is an emerging method in livestock and domestic animal research. HRV reflects the autonomic regulation of cardiac activity, in particular, the vagal (parasympathetic nervous system) tone.
  • The stress levels of six pregnant Przewalski’s horses from one harem in the Hortobágy National Park in Hungary were examined over one year.
  • A specific telemetry system was used for data collection which involved a subcutaneously implanted transmitter and a receiver fitted in a collar to chronicle HRV, heart rate, subcutaneous body temperature, and physical activity.
  • The measure of stress was defined as a reduction in parasympathetic nervous system tone, with root mean square of successive differences (RMSSD) being utilized to account for HRV.
  • Climate data was also captured in correspondence with the readings from the telemetry system. The data was then statistically analyzed using linear mixed effects models.

Findings

  • There were notable fluctuations in heart rate and HRV throughout the year, indicative of varied stress levels.
  • Substantially lower HR and HRV were observed during winter, a period associated with limited resources, hinting at reduced metabolic rates and heightened stress.
  • A drop in HRV and a peak in heart rate were observed in spring, illustrating an increased allostatic load. This was associated with rising energy demands during pregnancy and seasonal routines like gastrointestinal system adjustments to higher quality diets.

Conclusion

  • Tracking HRV telemetrically was confirmed as an effective way to observe the undisturbed reactions of wild animals to their changing environments over the long term.
  • The study deduced that Przewalski’s horses experience a decrease in complexity in their cardiovascular dynamics during winter and particularly spring, signaling seasonal stress.

Cite This Article

APA
Pohlin F, Brabender K, Fluch G, Stalder G, Petit T, Walzer C. (2017). Seasonal Variations in Heart Rate Variability as an Indicator of Stress in Free-Ranging Pregnant Przewalski’s Horses (E. ferus przewalskii) within the Hortobágy National Park in Hungary. Front Physiol, 8, 664. https://doi.org/10.3389/fphys.2017.00664

Publication

Frontiers in physiology
ISSN: 1664-042X
NlmUniqueID: 101549006
Country: Switzerland
Language: English
Volume: 8
Pages: 664
PII: 664

Researcher Affiliations

Pohlin, Friederike
  • Department of Integrative Biology and Evolution, Research Institute of Wildlife Ecology, University of Veterinary Medicine ViennaVienna, Austria.
Brabender, Kristin
  • Hortobagy National ParkHortobágy, Hungary.
Fluch, Gerhard
  • Department of Integrative Biology and Evolution, Research Institute of Wildlife Ecology, University of Veterinary Medicine ViennaVienna, Austria.
Stalder, Gabrielle
  • Department of Integrative Biology and Evolution, Research Institute of Wildlife Ecology, University of Veterinary Medicine ViennaVienna, Austria.
Petit, Thierry
  • Zoo de la PalmyreLes Mathes, France.
Walzer, Chris
  • Department of Integrative Biology and Evolution, Research Institute of Wildlife Ecology, University of Veterinary Medicine ViennaVienna, Austria.
  • Wildlife Conservation SocietyBronx, NY, United States.

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