Original Research
Analysis of Behaviors Observed During Mechanical Nociceptive Threshold Testing in Donkeys and Horses

https://doi.org/10.1016/j.jevs.2016.11.001Get rights and content

Highlights

  • We compared behaviors in donkeys and horses and videoed, while a noxious stimulus applied.

  • Behaviors during tests were observed which indicated the animals perceived the stimulus as noxious.

  • Foot lifts were a consistent end point.

  • Other behaviors preceded the foot lift suggesting it was not a reflex withdrawal response.

Abstract

The aims of the study were to analyze and compare behaviors in horses and donkeys observed during nociceptive threshold tests with a mechanical stimulus applied to the limb. The purpose was to identify end point behaviors suggesting the animals had perceived the stimulus to be noxious. Six male castrated horses (aged 3–4 years, weighing 415–503 kg) and eight castrated male donkeys (aged 4–9 years, weighing 152.5–170.5 kg) were studied. Video data recorded during mechanical nociceptive threshold test were analyzed by a single observer. Behaviors were classified into short-duration event behaviors and longer duration activity/state behaviors. Frequency of behaviors within a test (event behaviors) and percentage time spent during the test (activity/state behaviors) were calculated. Data were compared between horses and donkeys using Mann–Whitney tests (nonparametric data) or t-test (parametric data). Significance was taken as P < .05. Behaviors during the tests were observed which could indicate the animals perceived the stimulus as noxious. These included flattening ears back against the head, and turning the head (horses) and chewing (donkeys) although these were not consistent across both species. Foot lifts were often preceded by other behaviors which suggests that the foot lift was not purely a reflex withdrawal response. A shift in weight toward the contralateral limb was a consistent prodromal sign for an end point foot lift.

Introduction

In recent years, there has been increasing interest in behavioral expression of pain in donkeys. Regan et al [1] constructed an ethogram that was used to record behaviors in working donkeys. Certain behaviors changed in response to the administration of a nonsteroidal anti-inflammatory drug which suggested that these behaviors may be an expression of pain. Olmos et al [2] used a checklist of pain-related behaviors that correlated with abnormal and potentially painful lesions found on postmortem examination of donkeys in a donkey sanctuary. The findings of Regan et al [1] and Olmos et al [2] do suggest that donkeys may exhibit a wider repertoire of pain behavior than previously described in the literature [3], although the behaviors appear to be more subtle than those exhibited by other equidae.

To compliment behavioral assessments, nociceptive threshold testing (NTT) has been evaluated in the donkey [4], [5], [6], [7], aiming to objectively measure the functional state of the nociceptive system. Nociceptive threshold testing is an objective method for investigation of threshold responses to different noxious stimuli and evaluates the somatosensory system in its entirety, including nociceptors, peripheral nerves, the spinal cord, brain stem, thalamus, and cortex [8]. When choosing a stimulus, it should be repeatable, reliable, and easy to apply without producing lasting harm to the animal [9]. When evaluating different NTT modalities, end point behaviors need to be established. These are clear behavioral responses performed in response to the noxious stimulus, indicating that the animal has perceived the stimulus to be noxious.

Difficulty in interpreting end point behaviors in donkeys was found when developing different NTT methodologies. In thermal threshold testing using the withers site and visceral NTT using a rectal balloon model, testing was discontinued after initial pilot studies, in part due to the difficulty of interpreting and recognizing end point behaviors [5], [7]. Mechanical and thermal NTT using the limb site were both initially more successful models, with foot lifts seen as end point behaviors in all tests where the animals responded [4], [6], [7]. The foot lift response has also been used in other species as an end point in mechanical NTT limb testing, for example, cattle [10], horses [11], and sheep [12]. This may represent a “complex” behavioral response to noxious stimuli, suggesting that perception of the stimulus has taken place or some may regard this response as a withdrawal reflex.

Given the subtlety of behavioral expression of pain in the donkey compared with the horse [3], [13], one possibility is that other behaviors, which were cues that the animal had perceived the stimulus as noxious and therefore should have been interpreted as an end point behavior, were missed or misinterpreted. There have been no comparative studies between donkeys and horses analyzing their behavioral responses to identical painful stimuli. Pain, as defined by the International Association for the Study of Pain, is an “unpleasant sensory and emotional experience.” The measurement of nociceptive thresholds tests the sensitivity of the somatosensory pathways and can be standardized across the two species, but NTT does not measure any emotional experience that accompanies nociception. Such emotional experiences cannot be measured directly [14], although indices such as behavioral analysis can be used to try and identify the affective state of the animal along with the presence or absence of pain.

This study describes the analysis of data generated from videotaped behaviors during the application of the noxious mechanical stimulus to the limbs of horses and donkeys. The first aim of the study was to analyze behaviors observed during mechanical NTTs to try to identify behaviors other than a foot lift that may have suggested the donkey had perceived the stimulus to be noxious. This would in turn help identify alternative end point behaviors for future NTT in the donkey and establish whether the end point foot lift is a withdrawal reflex or involves higher cognitive function. The second aim of the study was to compare behavioral responses to mechanical NTTs in horses and donkeys.

Section snippets

Ethical Approval

This study received ethical approval from the University of Bristol (UB/10/019) and Ross University School of Veterinary Medicine (RUSVM) Institutional Animal Care and Use Committee.

Animals

Six male castrated horses (aged 3–4 years, weighing 415–503 kg) and eight castrated male donkeys (aged 4–9 years, weighing 152.5–170.5 kg) were studied at the Large Animal Research Park (LARP) at RUSVM on the island of St Kitts in the West Indies. The donkeys had been at the LARP facility for at least 6 months and

Results

Video data were collected from 256 tests in eight donkeys and 176 tests in six horses, of which 15 and 7 tests (respectively) were excluded from analysis due to poor quality video footage (e.g., inaudible “start cue” or animals moving out of the line of sight so that it was not possible to record behavior by moving the camera). Camera repositioning was required in 8 (donkeys) and 12 (horses) tests which were included in analysis. End point behaviors in the donkeys were consistently foot lifts

Discussion

This is the first analysis of behaviors during mechanical NTT in both the donkey and the horse. Mechanical NTT using the distal limb as the testing site has been described previously in horses [11] and donkeys [6]. This site was chosen as there is little anatomic variation between species and little soft tissue (which could spread the applied force) between the skin and the periosteum. The convexity of the actuator and the boot used to secure the actuator against the limb was different between

Conclusion

End point foot lifts were often preceded by other behaviors which suggests that the foot lift was a more complex response, rather than a simple withdrawal reflex, and therefore is an appropriate end point for NTT in the donkey and the horse. A shift in weight toward the contralateral limb was a consistent prodromal sign for an end point foot lift in both donkeys and horses. Behaviors during the tests were observed which seem to indicate the animals perceived the stimulus as noxious. Horses

Acknowledgments

This project was supported by Top Cat Metrology Ltd, RUSVM Research Department, Langford Trust, AVA Educational Trust, Vetronics, Pfizer, Boehringer Ingelheim, and Vetoquinol.

The authors would like to thank Dr Tammi Krecek and the research assistants at RUSVM for their support.

References (38)

  • B. Graf et al.

    Behavioural and physiological responses of calves to dehorning by heat cauterisation with or without local anaesthesia

    Appl Anim Behav Sci

    (1999)
  • M. Hay et al.

    Assessment of pain induced by castration in piglets; behavioural and physiological responses over the subsequent 5 days

    Appl Anim Behav Sci

    (2003)
  • C. Grant

    Behavioural responses of lambs to common painful husbandry procedures

    Appl Anim Behav Sci

    (2004)
  • N. Reefmann et al.

    Ear and tail postures as indicators of emotional valence in sheep

    Appl Anim Behav Sci

    (2009)
  • M.C. Leach et al.

    Behavioural effects of ovariohysterectomy and oral administration of meloxicam in laboratory housed rabbits

    Res Vet Sci

    (2009)
  • P.J. Mueller et al.

    Chewing behaviour in the domestic donkey (Equus asinus) fed fibrous forage

    App Anim Behav Sci

    (1998)
  • L. Proops et al.

    Social relations in a mixed group of mules, ponies and donkeys reflect differences in equid type

    Behav Processes

    (2012)
  • F.H. Regan et al.

    Behavioural repertoire of working donkeys and consistency of behaviour over time, as a preliminary step towards identifying pain-related behaviours

    PLoS One

    (2014)
  • Olmos G, Alvarado-Arellano AQ, Du Toit N. A novel approach of pain recognition and assessment in donkeys; initial...
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    Present address for T Beths: University of Melbourne, School of Veterinary Medicine, Werribee, Victoria, Australia.

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