Eye Blink Rates and Eyelid Twitches as a Non-Invasive Measure of Stress in the Domestic Horse

Merkies, Katrina; Ready, Chloe; Farkas, Leanne; Hodder, Abigail J.

doi:10.3390/ani9080562

Cited by 46 publications

(60 citation statements)

References 39 publications

(47 reference statements)

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“…A hierarchy of behavioural indicators with increasing stress was found in stabled horses [9], which coupled observable behaviours with physiological measures. Indicators might be subtle, for example eye "wrinkling", eyelid "twitches" and blink rate [10,11], or more overt such as bucking, head-tossing or rearing for example [12]. Reference [12], a detailed review of studies of behaviours of ridden horses, also concluded that individual differences between horses and inconsistencies amongst researchers (e.g.…”

Section: Introductionmentioning

confidence: 99%

Improving the Recognition of Equine Affective States

Bell¹,

Rogers²,

Taylor³

et al. 2019

Animals

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A key welfare problem for horses is that people commonly fail to recognise, and consequently neglect to resolve, equine behavioural signs of distress, worsening the welfare of the horse and potentially putting the safety of the handler at risk as a result. Members of equestrian Facebook groups were asked to view six videos and assess the horse’s behaviour in each; the authors selected the videos and considered each video to demonstrate behaviour associated with negative affective states. An additional six equine behaviourists also completed the survey as an “expert comparison group” from whom we could define “correct” answers; their responses were consistent with each other and the views of the authors. Although the majority of respondents successfully recognised behaviour indicative of distress in some instances, behaviour associated with negative affective states was commonly missed; videos featuring natural horsemanship and bridle-less riding were particularly interpreted incorrectly to be positive experiences for the horses. Binary logistic regression analysis (72.1% success rate) confirmed that the different video types (ridden dressage, natural horsemanship, in-hand dressage, bridle-less riding, Western reining and behavioural rehabilitation) were strong predictors for obtaining a correct answer (p < 0.01) but that experience of equine-ownership was not. Of the equestrian activities preferred by participants, only proponents of clicker training showed an increased likelihood of obtaining the correct answer (p = 0.05). Even when behavioural signs suggestive of negative affective states were recognised, a minority of respondents stated that they would be happy for their horse to be treated similarly. In conclusion, behavioural signs of equine distress are poorly recognised; they therefore warrant an increased prominence in education and the outreach activity of welfare organisations, in order to reduce equine suffering.

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Section: Introductionmentioning

confidence: 99%

Improving the Recognition of Equine Affective States

Bell¹,

Rogers²,

Taylor³

et al. 2019

Animals

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“…An earlier study also reported an increase in blinks during stressful situations [16]. However, Merkies et al [17] found instead that full blink diminished during stress. In this study, the increase was only statistically significant for the Co-occurrence method during transportation stress.…”

Section: Discussionmentioning

confidence: 99%

“…Stress induces typical facial expressions in humans [14], but only a few studies of facial expressions during stress have been performed in horses, most focusing on features around the eye [15] or blinking frequency to determine stress. However, there is some controversy on whether the frequency of blinks increases [16] or diminishes [17] during stress. Pain is an internal stressor and the experience of pain may therefore elicit a stress response.…”

Section: Introductionmentioning

confidence: 99%

Facial expressions of emotional stress in horses

Lundblad

Rashid

Rhodin

et al. 2020

Preprint

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Horses have the ability to generate a remarkable repertoire of facial expressions, some which have been linked to certain emotional states, for example pain. Studies suggest that facial expressions may be a more ‘honest’ expression of emotional state in horses than behavioral or physiological parameters. This study sought to describe the facial expressions during stress of healthy horses free of pain, using a standardized method of recording facial expressions in video. Stress was induced in 28 horses by subjecting them to road transport and 10 of these horses were also subjected to social isolation. The horses served as their own control. A body-mounted, remote controlled heart rate monitor provided continuous heart rate measurements during the interventions. The horses’ facial expressions were video-recorded during the interventions. Frequency and duration of each facial expression were then determined, according to the Equine Facial Action Coding System. Heart rate increased during the stressful interventions (p=0.01), confirming that the interventions were stressful. Using both the human investigation- and the co-occurrence methods, the following facial traits could be observed during stress: eye white increase (p<0.001), nostril dilator (p<0.001), upper eyelid raiser (p<0.001), inner brow raiser (p=0.042), tongue show (p<0.001) along with an increase in ‘ear flicker’ (p<0.001) and blink frequency (p<0.001). The facial actions were successfully used to train a machine-learning classifier to discriminate between stressed and calm horses, with an accuracy of 74.2 %. Most of the facial features identified correspond well with previous research on the subject, for example flared nostrils, repetitive mouth behaviors, increased eye white, tongue show and ear movements. Some features selected as indicative of emotional pain-free stress are used in face-based pain assessment tools, such as dilated nostrils, eye white increase or inner brow raiser. The relation between facial expressions of stress and pain should therefore further be studied.

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“…The action takes place in less than half a second [14]. Decreased eye blink rates has recently been associated to occurrence of stress or pain [22]. The Horse Grimace Scale [10] describes "Orbital Tightening: The eyelid is partially or completely closed".…”

Section: Discussionmentioning

confidence: 99%

“…The inner brow raiser (AU101) is also associated to characteristic changes in the eye region. The inner brow raiser is said to create a "triangular eye" or "worry wrinkles" [22,23], an appearance traditionally related to both stress and pain by horse care providers and veterinarians. Per definition, this muscle contraction increases the perceived size of the eye region, but not the aperture of the eye [14].…”

Section: Discussionmentioning

confidence: 99%

Equine Facial Action Coding System for determination of pain-related facial responses in videos of horses

Rashid

Silventoinen

Gleerup

et al. 2020

Preprint

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1AbstractDuring the last decade, pain scales including facial expressions as indicators of pain have been developed for horses, mostly relying on direct observations or inspection of images. Despite differences in the research conditions and methodology the different scales focus on the same regions of the face, corresponding to moveable facial muscles related to the ears, eyes, nostrils, lips and chin. However, a detailed comparison of the facial activities occurring during pain is not possible. We used a Facial Action Coding System modified for horses to code and analyse video recordings from an earlier study of acute short-term experimental pain and from clinical cases with and without pain. We demonstrated for the first time EquiFACS based changes to pain in video of horses, using traditional statistical methods based on frequency, and novel analyses based on sliding observation windows and co-occurrence of facial actions. The most prominent differences of the experimental horses were related to the lower face actions chin raiser and nostril dilator, while less prominent, but significantly more frequent actions were related to the eye region, inner brow raiser (AU101), increased eye white (AD1), half blink (AU47), and ear rotator (EAD104). Ears forward (EAD101) and eye blink (AU145) were not associated to pain. Based on this we selected the two lower face actions for analysis of the clinical videos, and found that their co-occurrence within a window of 10 to 15 second gave 100% positive predictive values, as compared to the rating from three expert pain raters. Using our developed co-occurrence analyses we were surprised to detect that the chance of identifying three or more of the facial actions related to pain in 0.04 second sequence, corresponding to one frame, was below 3%, indicating that use of randomly selected images for pain scoring may be a very insensitive method.

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Eye Blink Rates and Eyelid Twitches as a Non-Invasive Measure of Stress in the Domestic Horse

Cited by 46 publications

References 39 publications

Improving the Recognition of Equine Affective States

Improving the Recognition of Equine Affective States

Facial expressions of emotional stress in horses

Equine Facial Action Coding System for determination of pain-related facial responses in videos of horses

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