Topic:Facial Expressions
Facial expressions in horses are non-verbal cues that involve the movement of facial muscles and structures, such as the eyes, ears, nostrils, and mouth. These expressions can convey information about a horse's emotional state, intentions, or responses to external stimuli. The study of equine facial expressions involves analyzing specific movements and configurations, such as ear positioning or nostril flaring, to interpret behavioral and emotional contexts. Researchers utilize various methodologies, including observational studies and facial action coding systems, to systematically document and understand these expressions. This page compiles peer-reviewed research studies and scholarly articles that explore the anatomy, interpretation, and implications of facial expressions in equine behavior and welfare.
Facial Expressions of Horses Using Weighted Multivariate Statistics for Assessment of Subtle Local Pain Induced by Polylactide-Based Polymers Implanted Subcutaneously. Facial-expression-based analysis has been widely applied as a pain coding system in horses. Herein, we aimed to identify pain in horses undergoing subcutaneously polylactide-based polymer implantation. The sham group was submitted only to surgical incision. The horses were filmed before and 24 and 48 h after implantation. Five statistical methods for evaluating their facial expressions (FEs) were tested. Primarily, three levels of scores (0, 1, and 2) were applied to the seven FEs (ear movements, eyebrow tension, orbicularis tension, dilated nostrils, eye opening, muzzle tension, and masticato...
Can Ponies (Equus Caballus) Distinguish Human Facial Expressions? Communication within a species is essential for access to resources, alerting to dangers, group facilitation and social bonding; human facial expressions are considered to be an important factor in one’s ability to communicate with others. Evidence has shown that dogs and horses are able to distinguish positive and negative facial expressions by observing photographs of humans, however there is currently no research on how facial expressions from a live human are perceived by horses. This study investigated how ponies distinguish facial expressions presented by live actors. Trained actors (n...
Development of a Composite Pain Scale in Foals: A Pilot Study. Prompt pain management is crucial in horses; however, tools to assess pain are limited. This study aimed to develop and pilot a composite scale for pain estimation in foals. The "Foal Composite Pain Scale" (FCPS) was developed based on literature and authors' expertise. The FCPS consisted of 11 facial expressions, 4 behavioural items, and 5 physical items. Thirty-five pain-free foals (Control Group) and 15 foals experiencing pain (Pain Group) were used. Foals were video-recorded at different time points: the Control Group only at inclusion (C), while the Pain Group at inclusion (T1), after an ...
Pain assessment in horses using automatic facial expression recognition through deep learning-based modeling. The aim of this study was to develop and evaluate a machine vision algorithm to assess the pain level in horses, using an automatic computational classifier based on the Horse Grimace Scale (HGS) and trained by machine learning method. The use of the Horse Grimace Scale is dependent on a human observer, who most of the time does not have availability to evaluate the animal for long periods and must also be well trained in order to apply the evaluation system correctly. In addition, even with adequate training, the presence of an unknown person near an animal in pain can result in behavioral ch...
Measurement properties of grimace scales for pain assessment in nonhuman mammals: a systematic review. Facial expressions of pain have been identified in several animal species. The aim of this systematic review was to provide evidence on the measurement properties of grimace scales for pain assessment. The protocol was registered (SyRF#21-November-2019), and the study is reported according to the PRISMA guidelines. Studies reporting the development, validation, and the assessment of measurement properties of grimace scales were included. Data extraction and assessment were performed by 2 investigators, following the COnsensus-based Standards for the Selection of Health Measurement INstruments ...
Using the Judgment Bias Task to Identify Behavioral Indicators of Affective State: Do Eye Wrinkles in Horses Reflect Mood? Identifying and validating behavioral indicators of mood are important for the assessment of animal welfare. Here, we investigated whether horses' eye wrinkle expression in a presumably neutral situation is a measure of mood as assessed in a cognitive judgment bias task (JBT). To this end, we scored pictures of the left and right eyes of 16 stallions for different aspects of eye wrinkle expression and tested the same individuals on a spatial JBT with active trial initiation. Eye wrinkle expressions were assessed by a qualitative assessment, i.e., the overall assessment of how "worried" horses ...
Objective Assessment of Chronic Pain in Horses Using the Horse Chronic Pain Scale (HCPS): A Scale-Construction Study. The objective assessment of chronic pain is of utmost importance for improving welfare and quality of life in horses. Freedom from disease and pain is one of the 'five freedoms' that are necessary for animal welfare. The aim of this study was to develop a pain scale for the assessment of chronic pain in horses (Horse Chronic Pain Scale; HCPS), which is based on behavioural and facial expressions. The scale was used to assess 53 horses (26 horses diagnosed with chronic painful conditions by means of clinical examination and additional diagnostic procedures (consisting of osteoarthritis, chronic...
Development and validation of the facial scale (FaceSed) to evaluate sedation in horses. Although facial characteristics are used to estimate horse sedation, there are no studies measuring their reliability and validity. This randomised controlled, prospective, horizontal study aimed to validate a facial sedation scale for horses (FaceSed). Seven horses received detomidine infusion i.v. in low or high doses/rates alone (DL 2.5 μg/kg+6.25 μg/kg/h; DH 5 μg/kg+12.5 μg/kg/h) or combined with methadone (DLM and DHM, 0.2 mg/kg+0.05 mg/kg/h) for 120 min, or acepromazine boli i.v. in low (ACPL 0.02 mg/kg) or high doses (ACPH 0.09 mg/kg). Horses' faces were photographed at i) baseline,...
Towards Machine Recognition of Facial Expressions of Pain in Horses. Automated recognition of human facial expressions of pain and emotions is to a certain degree a solved problem, using approaches based on computer vision and machine learning. However, the application of such methods to horses has proven difficult. Major barriers are the lack of sufficiently large, annotated databases for horses and difficulties in obtaining correct classifications of pain because horses are non-verbal. This review describes our work to overcome these barriers, using two different approaches. One involves the use of a manual, but relatively objective, classification system for...
Interspecific two-dimensional visual discrimination of faces in horses (Equus caballus). In social animals, recognizing conspecifics and distinguishing them from other animal species is certainly important. We hypothesize, as demonstrated in other species of ungulates, that horses are able to discriminate between the faces of conspecifics and the faces of other domestic species (cattle, sheep, donkeys and pigs). Our hypothesis was tested by studying inter-and intra-specific visual discrimination abilities in horses through a two-way instrumental conditioning task (discrimination and reversal learning), using two-dimensional images of faces as discriminative stimuli and food as a p...
Towards an improved pain assessment in castrated horses using facial expressions (HGS) and circulating miRNAs. Pain in horses is an emergent welfare concern, and its assessment represents a challenge for equine clinicians. This study aimed at improving pain assessment in horses through a convergent validation of existing tools: we investigated whether an effective analgesic treatment influences the horse grimace scale (HGS) and the concentration of specific circulating microRNAs (miRNAs). Eleven stallions underwent routine surgical castration under general anaesthesia. They were divided into two analgesic treatment groups: castration with the administration of preoperative flunixin and castration with ...
Towards an improved pain assessment in castrated horses using facial expressions (HGS) and circulating miRNAs. Pain in horses is an emergent welfare concern, and its assessment represents a challenge for equine clinicians. This study aimed at improving pain assessment in horses through a convergent validation of existing tools: we investigated whether an effective analgesic treatment influences the horse grimace scale (HGS) and the concentration of specific circulating microRNAs (miRNAs). Eleven stallions underwent routine surgical castration under general anaesthesia. They were divided into two analgesic treatment groups: castration with the administration of preoperative flunixin and castration with ...
Identification of Body Behaviors and Facial Expressions Associated with Induced Orthopedic Pain in Four Equine Pain Scales. Equine orthopedic pain scales are targeted towards horses with moderate to severe orthopedic pain. Improved assessment of pain behavior and pain-related facial expressions at rest may refine orthopedic pain detection for mild lameness grades. Therefore, this study explored pain-related behaviors and facial expressions and sought to identify frequently occurring combinations. Orthopedic pain was induced by intra-articular LPS in eight horses, and objective movement asymmetry analyses were performed before and after induction together with pain assessments at rest. Three observers independently ...
Equine Facial Action Coding System for determination of pain-related facial responses in videos of horses. During the last decade, a number of pain assessment tools based on facial expressions have been developed for horses. While all tools focus on moveable facial muscles related to the ears, eyes, nostrils, lips, and chin, results are difficult to compare due to differences in the research conditions, descriptions and methodologies. We used a Facial Action Coding System (FACS) modified for horses (EquiFACS) to code and analyse video recordings of acute short-term experimental pain (n = 6) and clinical cases expected to be in pain or without pain (n = 21). Statistical methods for analyses were a f...
Objective Assessment of Acute Pain in Foals Using a Facial Expression-Based Pain Scale. Pain assessment is very important for monitoring welfare and quality of life in horses. To date, no studies have described pain scales for objective assessment of pain in foals. Studies in other species have shown that facial expression can be used in neonatal animals for objective assessment of acute pain. The aim of the current study was to adapt a facial expression-based pain scale for assessment of acute pain in mature horses for valid pain assessment in foals. The scale was applied to fifty-nine foals (20 patients and 39 healthy controls); animals were assessed from video recordings (30-6...
Objective Assessment of Acute Pain in Foals Using a Facial Expression-Based Pain Scale. Pain assessment is very important for monitoring welfare and quality of life in horses. To date, no studies have described pain scales for objective assessment of pain in foals. Studies in other species have shown that facial expression can be used in neonatal animals for objective assessment of acute pain. The aim of the current study was to adapt a facial expression-based pain scale for assessment of acute pain in mature horses for valid pain assessment in foals. The scale was applied to fifty-nine foals (20 patients and 39 healthy controls); animals were assessed from video recordings (30-6...
EEG based assessment of stress in horses: a pilot study. As has been hypothesized more than 20 years ago, data derived from Electroencephalography (EEG) measurements can be used to distinguish between behavioral states associated with animal welfare. In our current study we found a high degree of correlation between the modulation index of phase related amplitude changes in the EEG of horses ( = 6 measurements with three different horses, mare and gelding) and their facial expression, measured by the use of the horse grimace scale. Furthermore, the pattern of phase amplitude coupling (PAC) was significantly different between a rest condition and a s...
Does Thirty-Minute Standardised Training Improve the Inter-Observer Reliability of the Horse Grimace Scale (HGS)? A Case Study. The Horse Grimace Scale (HGS) is a facial-expression-based pain coding system that enables a range of acute painful conditions in horses to be effectively identified. Using valid assessment methods to identify pain in horses is of a clear importance; however, the reliability of the assessment is highly dependent on the assessors' ability to use it. Training of new assessors plays a critical role in underpinning reliability. The aim of the study was to evaluate whether a 30-minute standardised training program on HGS is effective at improving the agreement between observers with no horse experi...
Female horses spontaneously identify a photograph of their keeper, last seen six months previously. Horses are capable of identifying individual conspecifics based on olfactory, auditory or visual cues. However, this raises the questions of their ability to recognize human beings and on the basis of what cues. This study investigated whether horses could differentiate between a familiar and unfamiliar human from photographs of faces. Eleven horses were trained on a discrimination task using a computer-controlled screen, on which two photographs were presented simultaneously (32 trials/session): touching one was rewarded (S+) and the other not (S-). In the training phase, the S+ faces were of...
Horses feel emotions when they watch positive and negative horse-human interactions in a video and transpose what they saw to real life. Animals can indirectly gather meaningful information about other individuals by eavesdropping on their third-party interactions. In particular, eavesdropping can be used to indirectly attribute a negative or positive valence to an individual and to adjust one's future behavior towards that individual. Few studies have focused on this ability in nonhuman animals, especially in nonprimate species. Here, we investigated this ability for the first time in domestic horses (Equus caballus) by projecting videos of positive and negative interactions between an unknown human experimenter (a "positive" ...
Levelling playing field: synchronization and rapid facial mimicry in dog-horse play. Social play is a window on cognitive and communicative abilities of species. Inter-specific play, in particular, is a fertile venue to explore the capacity to correctly perceive and interpret signals emitted by partners. Up to now, most studies have focussed on dog-human play due to the important implications such studies have in understanding the peculiar relationship we establish with our pets. Here, we focussed on social play between dogs and horses. By using a set of specific keywords (dog, horse, play, friend) we selected 20 videos of dog-horse social play (with each session lasting >3...
Measuring the evolution of facial ‘expression’ using multi-species FACS. Darwin observed that form, and in his view, meaning, of facial behaviour (observable changes in the appearance of the face, often termed facial 'expression') is similar between a wide range of species and concluded that this must be due to a shared ancestral origin. Yet, as with all social behaviours, exactly how to define similarity and determine homology is debated. Facial behaviour is linked to specific facial muscle movements, so one important factor in determining homology is the anatomical basis of facial behaviours that appear similar in both appearance and social function. The Facial A...
Effect of work on body language of ranch horses in Brazil. The horses' responses to exercise are commonly monitored using physiological variables, nonetheless physical and mental states can also be expressed through body language. The aims of this study were: (i) to identify how facial expressions and other behavioural variables change in ranch horses after a routine workday, and (ii) to investigate if these changes can be used as indicators of physical tiredness by relating them to known variables of physical fitness and workload. Fourteen crossbred ranch horses were assessed pre- and post-workday on two farms, recording the body language, physiologi...
Use of rotational periosteal flaps in primary repair of sinofacial fractures in seven horses. Case history: Medical records were reviewed of horses (n = 7) undergoing surgery for fracture of one or more facial bones extending into the paranasal sinuses that was repaired primarily within 24 hours of the time of injury using a rotational periosteal flap, between April 2009 and May 2017. A kick from another horse was the cause of the injury of three horses, and one horse was injured when it collided with a tree. The cause of the injury of three horses was unknown.Clinical findings and treatment: Fractures were of the right maxillary bone in two horses, the left maxillary bone in two h...
Horses Categorize Human Emotions Cross-Modally Based on Facial Expression and Non-Verbal Vocalizations. Over the last few years, an increasing number of studies have aimed to gain more insight into the field of animal emotions. In particular, it is of interest to determine whether animals can cross-modally categorize the emotions of others. For domestic animals that share a close relationship with humans, we might wonder whether this cross-modal recognition of emotions extends to humans, as well. In this study, we tested whether horses could recognize human emotions and attribute the emotional valence of visual (facial expression) and vocal (non-verbal vocalization) stimuli to the same perceptua...
Trauma-induced exostosis of multiple suture lines causing partial bilateral nasolacrimal duct obstruction in a 7-year-old Thoroughbred mare. A definitive diagnosis of extensive suture line exostoses affecting the nasofrontal, nasolacrimal, nasomaxillary, frontolacrimal, lacrimozygomatic and lacrimomaxillary suture lines in a 7-year-old Thoroughbred mare with chronic bilateral epiphora and facial deformation was achieved using standing computed tomography (CT) examinations. Positive contrast dacryocystorhinography using CT revealed partial bilateral obstruction of the nasolacrimal ducts. Minimally displaced depression fractures of the right nasal bone, the right maxillary bone and right frontal bone were also demonstrated. The cosme...
Sex and Age Don’t Matter, but Breed Type Does-Factors Influencing Eye Wrinkle Expression in Horses. Identifying valid indicators to assess animals' emotional states is a critical objective of animal welfare science. In horses, eye wrinkles above the eyeball have been shown to be affected by pain and other emotional states. From other species we know that individual characteristics, e.g., age in humans, affect facial wrinkles, but it has not yet been investigated whether eye wrinkle expression in horses is systematically affected by such characteristics. Therefore, the aim of this study was to assess how age, sex, breed type, body condition, and coat colour affect the expression and/or the as...
Facial expression and oxytocin as possible markers of positive emotions in horses. Behavioural and physiological markers of discrete positive emotions remain little investigated in animals. To characterise new markers in horses, we used tactile stimulations to induce emotional situation of contrasting valence. In the Gentle grooming group (G, N = 13) horses were gently groomed during 11 sessions on the body areas they appreciated the most. Horses in the Standard grooming group (S, N = 14) were groomed using a fixed procedure, reported to induce avoidance reactions in some horses. At session 11, G horses expressed significantly more contact-seeking behaviours than S h...
Can grimace scales estimate the pain status in horses and mice? A statistical approach to identify a classifier. Pain recognition is fundamental for safeguarding animal welfare. Facial expressions have been investigated in several species and grimace scales have been developed as pain assessment tool in many species including horses (HGS) and mice (MGS). This study is intended to progress the validation of grimace scales, by proposing a statistical approach to identify a classifier that can estimate the pain status of the animal based on Facial Action Units (FAUs) included in HGS and MGS. To achieve this aim, through a validity study, the relation between FAUs included in HGS and MGS and the real pain co...