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As a remedy against stress and anxiety, cannabidiol (CBD) products are of increasing interest in veterinary medicine. Limited data is available describing the actual effectiveness of CBD in horses. The aim of this study (part 2 of 2) was to analyze stress parameters via behavioral observation, heart rate monitoring and assessment of blood and saliva cortisol levels in healthy horses treated repeatedly with a CBD containing paste. Twelve horses were randomly assigned to a treatment or a control group. Two pastes were orally administered in a double-blinded study design, one paste containing CBD and one paste without active ingredient. Both pastes were administered twice daily over 15 days (dose: 3 mg CBD/kg). Behavioral observations were conducted daily using a sedation score and a rating of facial expressions, based on the previously described facial sedation scale for horses (FaceSed) and the Horse Grimace Scale. Blood and saliva samples were obtained regularly to determine cortisol levels throughout the study. Cortisol levels were analyzed by means of liquid chromatography/tandem mass spectrometry (LC/MS/MS). Behavioral observations and cortisol levels were compared between groups. Prior to paste administration, a novel object test was performed and the horses’ reaction to loading on a trailer was recorded. Both tests were repeated after 13 days of paste application. Movement patterns such as different gaits during the novel object test were evaluated and an ethogram was designed to assess exhibited behavioral traits. Cardiac beat-to-beat (R-R) intervals were recorded throughout and evaluated using heart rate (HR) and heart rate variability (HRV) parameters. Blood and saliva samples for cortisol analysis were taken before and after the tests. Daily behavioral observations and cortisol levels did not differ between the treatment and the control group. Similarly, analysis of movement patterns, HR, HRV and cortisol levels during the novel object test and trailer test did not identify significant differences between the groups. Regularly administered oral CBD (3 mg/kg BID over 15 days) had no statistically significant effect on behavioral observations, cortisol levels, HR and HRV in horses. Further research is required to establish adequate doses and indications for the use of CBD in horses. [ABSTRACT FROM AUTHOR]

As a remedy against stress and anxiety, cannabidiol (CBD) products are of increasing interest in veterinary medicine. Limited data is available describing the actual effectiveness of CBD in horses. The aim of this study (part 2 of 2) was to analyze stress parameters via behavioral observation, heart rate monitoring and assessment of blood and saliva cortisol levels in healthy horses treated repeatedly with a CBD containing paste. Twelve horses were randomly assigned to a treatment or a control group. Two pastes were orally administered in a double-blinded study design, one paste containing CBD and one paste without active ingredient. Both pastes were administered twice daily over 15 days (dose: 3 mg CBD/kg). Behavioral observations were conducted daily using a sedation score and a rating of facial expressions, based on the previously described facial sedation scale for horses (FaceSed) and the Horse Grimace Scale. Blood and saliva samples were obtained regularly to determine cortisol levels throughout the study. Cortisol levels were analyzed by means of liquid chromatography/tandem mass spectrometry (LC/MS/MS). Behavioral observations and cortisol levels were compared between groups. Prior to paste administration, a novel object test was performed and the horses’ reaction to loading on a trailer was recorded. Both tests were repeated after 13 days of paste application. Movement patterns such as different gaits during the novel object test were evaluated and an ethogram was designed to assess exhibited behavioral traits. Cardiac beat-to-beat (R-R) intervals were recorded throughout and evaluated using heart rate (HR) and heart rate variability (HRV) parameters. Blood and saliva samples for cortisol analysis were taken before and after the tests. Daily behavioral observations and cortisol levels did not differ between the treatment and the control group. Similarly, analysis of movement patterns, HR, HRV and cortisol levels during the novel object test and trailer test did not identify significant differences between the groups. Regularly administered oral CBD (3 mg/kg BID over 15 days) had no statistically significant effect on behavioral observations, cortisol levels, HR and HRV in horses. Further research is required to establish adequate doses and indications for the use of CBD in horses.

Cannabidiol (CBD) products have been proposed to exert stress- and anxiety-relieving effects in animals. Despite the increasing popularity of CBD for veterinary use, the available research detailing the effects of CBD in horses is limited. The aim of this study (part 1 of 2) was to analyze stress parameters via behavioral observations and heart rate monitoring in healthy horses following single oral administration of a CBD containing paste in different doses. Study products were two pastes for oral administration, one containing CBD and one containing no active ingredient. Pastes were applied as single administrations in consecutive trials with escalating dosages (doses: 0.2, 1.0, 3.0 mg CBD/kg) to a treatment (trial 1: n = 3, trial 2: n = 3, trial 3: n = 5 horses) and a control group (trial 1: n = 3, trial 2: n = 3, trial 3: n = 6 horses) with minimum wash-out periods of seven days in between. Behavioral parameters were evaluated using video recordings to score the levels of sedation including the horses' reactions to acoustic and visual stimuli. Facial expression was assessed using photographs. Evaluation was based on the previously described facial sedation scale for horses (FaceSed) and the Horse Grimace Scale. For baseline values, identical observations were recorded on the day before each paste administration. Both paste administration and behavioral evaluation were performed double blinded. Cardiac beat-to-beat (R-R) intervals were continuously recorded throughout the trial and assessed using heart rate and heart rate variability parameters. Statistical analysis included comparison between treatment and control group over escalating doses and time points using linear mixed models. The CBD paste was well tolerated, and no side effects were observed. Analysis of sedation scores and facial expressions did not indicate significant differences between treatment and control group over the escalating doses. The heart rate was neither reduced, nor were significant changes in heart rate variability observed compared to the control group. Main limitation of this study is the small sample size. Further research is required to determine adequate doses and indications for the use of CBD products in horses.

Simple Summary: Fatal injuries in Thoroughbred racehorses typically occur due to an accumulation of bone damage, however, detecting their impending onset can be difficult as there are often no overt signs. In other horse populations, facial grimacing has been shown to be associated with orthopaedic pain. This study, therefore, aimed to investigate facial expressions of Thoroughbred racehorses at the trot to identify if there were subtle signs of pain in mildly lame compared to non-lame horses. Two independent observers assessed 22 facial expression parameters using still photographs of the head from video-recorded trot-ups. There were few expressions associated with lameness except for more exposed whites of the eye in lame horses. Thus, facial pain scoring may not be adequate for the detection of subtle lameness in racehorses who work in a racing stable environment. Musculoskeletal injuries in racehorses are difficult to detect prior to catastrophic breakdown. Lameness is commonly attributed to orthopaedic pain in horses, therefore, subtle lameness may be a pre-clinical sign of injury and, if identified early, could allow for preventative intervention. Our objective was to determine if facial expressions could be used to detect mild lameness as an indicator of orthopaedic pain in 'fit to race' horses. The Horse Grimace Scale (HGS) and the facial expressions in ridden horses (FEReq), were used to score images (n = 380) of mildly lame (n = 21) and non-lame (n = 17) Thoroughbred horses by two independent observers. Using an Equinosis Lameness Locator®, the lameness status of each horse was determined according to published thresholds [forelimb lameness (>|14.5 mm|) and hindlimb lameness (>|7.5 mm|)]. Inter and intraobserver reliability were assessed using two-way random-effects models. Univariable associations between lameness and facial expression parameters were identified using logistic and linear regression. Interobserver reliability was moderate (κ 0.45; 95% CI 0.36, 0.55). Horses with moderate mouth strain (HGS) and tense and extended upper lip (FEReq) were less likely to be lame (p = 0.042 and p = 0.027, respectively). Exposed sclera was associated with lameness (p = 0.045). Higher orbital tightening (HGS) scores were associated with a lower degree of maximum head amplitude (HDmax) lameness (p = 0.044). Tension and moderate tension above the eye, for the HGS and FEReq scores, were associated with increasing amplitude of HDmax (p = 0.048 and p = 0.034, respectively). Inconsistent associations between lameness status and HGS and FEReq scores may limit the potential use of the facial expression for the prediction of mild orthopaedic pain during pre-race lameness examinations. More objective parameters associated with mild orthopaedic pain should be explored. [ABSTRACT FROM AUTHOR]

Simple Summary: Stomach ulcers (known as equine gastric ulcer syndrome [EGUS]) are a common finding in horses However, the amount of pain horses with EGUS might experience is currently unknown and this knowledge could allow for better clinical decision making and improved horse welfare. The study aim was to assess the use of a pain scale score system, the Horse Grimace Scale (HGS), in horses suffering from EGUS. Facial photographs for HGS evaluation were taken of all horses. Gastroscopy is the gold standard procedure for diagnosis of EGUS, and involves examining the stomach with a video-endoscope. Horses (n = 61) were divided into groups based on the presence and severity of EGUS as determined via gastroscopy. Horses with concurrent lameness or other signs of illness were excluded. Comparisons were made of the HGS between horses, with and without gastric lesions. This is the first study investigating the use of the HGS in horses with and without EGUS. The HGS scores were not influenced by the presence or severity of EGUS and no significant differences were noted between groups. Further studies investigating the use of different pain scales in horses with EGUS are needed. Equine gastric ulcer syndrome (EGUS) is a highly prevalent and presumptively painful condition, although the amount of pain horses might experience is currently unknown. The aims of this study were to determine if the Horse Grimace Scale (HGS) could identify pain behaviours in horses with and without EGUS and if severity would be positively associated with the HGS score. Horse grimace scale scores were assessed blindly using facial photographs by seven observers and involved evaluation of 6 facial action units as 0 (not present), 1 (moderately present) and 2 (obviously present). Lameness examination, serum amyloid A (SAA) measurement and gastroscopy evaluation were performed on all horses. Horses (n = 61) were divided into two and three groups based on the presence (yes, no) and severity (none, mild, moderate-severe) of EGUS, respectively. Presence of lameness and elevated SAA (≥50 µg/mL) were used as exclusion criteria. Inter-observer reliability was analyzed by intra-class correlation coefficients (ICC). HGS scores between groups were compared using Welch's and Brown Forsythe tests (p < 0.05). Overall, HGS ICC was "excellent" (0.75). No significant differences (p = 0.566) were observed in HGS scores between horses with and without gastric lesions (mean, 95% CI; 3.36, 2.76–3.95 and 3, 1.79–4.20, respectively). HGS was not influenced by the presence or severity of EGUS in this current study. Further studies investigating the use of different pain scales in horses with EGUS are needed. [ABSTRACT FROM AUTHOR]

To assess the reliability of a French version of the Horse Grimace Scale (HGSfv). Prospective, randomized, clinical study. The operated (OP) group included 13 horses undergoing elective surgery. The positive (PC) and negative control (NC) groups included seven colicking horses and eight exercising sport horses, respectively. Photographs were extracted from videos of the horses' heads. Videos were taken before and immediately after surgery in OP, on arrival of the horse in PC, and at rest in their stalls in NC. Pictures were evaluated by three anaesthetists [Diplomates (DIPs)] and four riders (RIDs) using Horse Grimace Scale translated into French (HGSfv) at two points, 2 weeks apart (E1 and E2). Each evaluator gave each image a score (1–3) for six identified facial action units. The scores given by DIPs and RIDs were compared using a Wilcoxon test. Intra- and inter-evaluator reliability were assessed using Spearman correlation tests (r s) and intra-class coefficients (ICCs), respectively. RIDs and DIPs gave significantly higher scores in the PC group than in the NC group [RIDsE1PC 5.0 (4.2–9.8) versus RIDsE1NC 2.2 (0.0–6.5), p = 0.02; RIDsE2PC 5.2 (3.2–9.5) versus RIDsE2NC 2.0 (0.2–5.8), p < 0.01; DIPsE1PC 4.0 (1.3–6.3) versus DIPsE1NC 2.2 (1.0–4.7), p = 0.04; DIPsE2PC 2.7 (1.0–6.0) versus DIPsE2NC 1.0 (0.0–2.3), p = 0.03 ]. Scores given by RID or DIPs 2 weeks apart were highly correlated [ r s (RIDsE1, RIDsE2) r = 0.86, p < 0.0001] and [ r s (DIPsE1, DIPsE2) r = 0.81 p < 0.0001]. The ICC between RIDs and DIPs in E1 and E2 was 0.94 (0.92–0.95) and 0.91 (0.89–0.93), respectively. The specificity and sensitivity of the HGSfv was 94% and 43%, respectively. Using the HGSfv, knowledge of horses rather than specialization in veterinary anaesthesia and analgesia appears to differentiate horses with visceral pain from those assumed to be pain free. [ABSTRACT FROM AUTHOR]

Copyright of Revista Academica Ciencia Animal is the property of Revista Academica Ciencia Animal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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 (n = 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 stress condition in horses. This pilot study paves the way for a possible use of EEG derived PAC as an objective tool for the assessment of animal welfare. Beyond that, the method might be useful to assess welfare aspects in the clinical setting for human patients, as for example in the neonatal intensive care unit.

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 (n = 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 stress condition in horses. This pilot study paves the way for a possible use of EEG derived PAC as an objective tool for the assessment of animal welfare. Beyond that, the method might be useful to assess welfare aspects in the clinical setting for human patients, as for example in the neonatal intensive care unit. [ABSTRACT FROM AUTHOR]

Horse handlers often encounter problem behaviour resulting from a lack of stimulus control. Handlers are often only 15% of the weight of horses, which evolved strong flight responses. Therefore, many riders and handlers resort to the use of “aids” to maintain control of their animals. However, there are increasing concerns about the efficacy and welfare implication of such devices, particularly when applied to sensitive facial structures. One such device is a Dually ® headcollar which aims to increase compliance. Despite its popularity, little is known about the effects of this aid on behaviour or stress. The aim of the current study was to determine whether the use of a Dually headcollar improves compliance during handling and, if so, whether this might be achieved with concomitant increases in stress or discomfort. Subjects completed two novel handling tests, one wearing a Dually with a line attached to the pressure mechanism and one attached to the standard ring as a Control. Crossing time and proactive behaviour were recorded as indicators of compliance. Core temperature and the discrepancy between eye temperatures were measured using IRT before and after testing as an indicator of stress. The Horse Grimace Scale (HGS) was used to measure discomfort caused by each configuration of the device. The Dually did not result in more compliant behaviour, compared to the Control (p = 0.935; p = 0.538). However, the Dually configuration did result in a significantly higher HGS scores (p = 0.034). This may indicate that there is an impact on animal welfare by using this device that is not justified by improved behaviour. However, IRT readings of core temperature (p = 0.186) and discrepancy between the eyes (p = 0.972) did not indicate the Dually increased stress in subjects. Taken together, this suggests the Dually is ineffective in naïve horses but causes increased discomfort. [ABSTRACT FROM AUTHOR]

Riding schools play an essential role in the equestrian industry and in education. These establishments are reliant on horses to work for numerous hours, often with riders of different abilities. However, little is known about the impact workload has on the well-being of these horses and effective monitoring of welfare is required for animal-based industries to maintain their Social Licence to Operate. The aim of the current study was to investigate how the quantity of work carried out by riding school horses affects their behaviour and physiology, providing evidence as a starting point to identify suitable levels of work that riding school horses can be used for before their welfare is compromised. Horses (n = 30) were observed 1–2 h after completing their workload on a day of Rest, Moderate (1–2 h) and Hard work (3–4 h). Infrared thermography of eye temperature (IRT) and heart rate variability (RMSSD) were measured as indicators of arousal. The Horse Grimace Scale (HGS) was scored treatment-blind to measure discomfort and pain. No significant difference was found between RMSSD or eye temperature depending on the level of workload, indicating subjects were able to cope with increasing demands. However, there was a significant difference in the HGS score between Rest, Moderate and Hard work (p < 0.001). This indicates a greater degree of discomfort following an increase in hours of work. Another possible explanation for the increase of the HGS score is that tiredness can influence the presence of some of the FAUs (e.g., backward ears and orbital tightening) making it more difficult to discriminate between whether a horse was in pain or the increased score is a consequence of being physically tired after the work. Findings indicate that 1–2 days of working 3–4 h can be appropriate in horses conditioned to the work in well managed riding facilities, however further research is needed to determine how long increased HGS lasts to determine how often days of hard work may occur without impacting welfare. • Riding school horses work long hours carrying beginners with poor control of their weight and aids. • Industries must evidence that animal use is humane to maintain their Social Licence to Operate. • Riding school horses (n = 30) observed on day of Rest, Moderate (1–2 hrs) and Hard (3–4hrs) workload. • Heart rate variability (HRV), eye temperature (IRT) and Horse Grimace Scale (HGS) measured. • HRV and RMSSD did not change but HGS was significantly higher on both Moderate and Hard work days. [ABSTRACT FROM AUTHOR]

The Horse Grimace Scale (HGS) is a facial-expression–based pain coding system that incorporates six Facial Action Units, independently scored. The aim of this pilot study was to determine whether HGS score changed in response to emotional states other than pain. Seven riding school horses were exposed to different experimental conditions that are known to elicit different emotional states (new environment, grooming, anticipation of food reward, fear). As a control, videos were also recorded with the horse undisturbed in their home environment. Videos were recorded in each experimental condition and individual frames were captured from HD video files. Thirty-five pictures were scored using HGS by three experimental design blind observers. The results showed that the HGS score did not change in any of the experimental conditions when compared with control. In all the conditions but one (fear), the mean HGS score was low (≤2 on a maximum score of 12), but not zero; the scores of stiffly backward ears and prominent strained chewing muscles tended to be higher in fear than in other conditions. Although these are preliminary results as the number of tested horses is limited, HGS seems to be a specific tool to assess pain in horses. Changes in ear posture and tension in chewing muscles tend to be present in negative emotional states such as fear; therefore, a larger scale study is needed to collect data from the same horses in positive and negative situations, including pain. [ABSTRACT FROM AUTHOR]

Much like humans, horses possess the ability to generate a wide range of facial behaviors. These expressions are a form of communication used to convey substantial amounts of information to other members of the herd, including stress. A variety of studies have developed ethograms to quantify the degree of facial behaviors expressed as a means of assessing the welfare of the horse. This is particularly important in working horses, such as those involved in equine assisted activities (EAA). The objective of this study was to use the Horse Grimace Scale (HGS) to assess the stress response of horses involved in EAA by numerically scoring facial muscular tension. The HGS is a scale that focuses on 6 specific facial action units to evaluate the degree of pain and distress experienced by a horse. Each unit was given a score of 0 (not present), 1 (moderately present), or 2 (obviously present). The highest possible score was 12, indicating the greatest degree of pain. Horses trained in EAA (EAA, n = 6) were paired with a veteran with posttraumatic stress disorder (PTSD) for a 30-min weekly lesson or assigned as astanding non-EAA trained control (CON, n = 6) for the duration of 8 wks. Images of the profile of the horses were taken at 3 time points during the lesson: 10 min, 20 min, and 30 min after the start of the session. After the sessions, images were organized and redacted if necessary and scored by 4 independent raters who had received training on the use of the HGS. Score data were analyzed using a negative binomial mixed model, repeated measures ANOVA with fixed effects of treatment (EAA vs CON), session, and time point, and their interactions and a random effect of horse. Intraclass correlation coefficient for inter-rater agreement was 0.446 (P = 2.17e-59). Statistically different means were separated using Tukey's method. Significance was set at P ≤ 0.05. Scores were higher (P = 0.0178) in wk 4 (5.2 ± 0.4, mean ± SE) than wk 1 (3.7 ± 0.4) among CON horses. No other significant differences were found. Participation in EAA did not appear to have an adverse effect on horses as defined by pain and distress scores on the HGS. [ABSTRACT FROM AUTHOR]

Acute laminitis is a common equine disease characterized by intense foot pain, both acutely and chronically. The Obel grading system is the most widely accepted method for describing the severity of laminitis by equine practitioners, however this method requires movement (walk and trot) of the horse, causing further intense pain. The recently developed Horse Grimace Scale (HGS), a facial-expression-based pain coding system, may offer a more effective means of assessing the pain associated with acute laminitis. The aims of this study were: to investigate whether HGS can be usefully applied to assess pain associated with acute laminitis in horses at rest, and to examine if scoring HGS using videos produced similar results as those obtained from still images. Ten horses, referred as acute laminitis cases with no prior treatment, were included in the study. Each horse was assessed using the Obel and HGS (from images and videos) scales: at the admission (before any treatment) and at seven days after the initial evaluation and treatment. The results of this study suggest that HGS is a potentially effective method to assess pain associated with acute laminitis in horses at rest, as horses showing high HGS scores also exhibited higher Obel scores and veterinarians classified them in a more severe painful state. Furthermore, the inter-observer reliability of the HGS total score was good for both still images and video evaluation. There was no significant difference in HGS total scores between the still images and videos, suggesting that there is a possibility of applying the HGS in clinical practice, by observing the horse for a short time. However, further validation studies are needed prior to applying the HGS in a clinical setting. [ABSTRACT FROM AUTHOR]

Copyright of Revista Acadêmica: Ciência Animal is the property of Revista Academica: Ciencia Animal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista Acadêmica: Ciência Animal is the property of Revista Academica: Ciencia Animal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Dually headcollars increase pressure, intended to improve compliance in horses. • Horses did not complete handling tests faster in the Dually, compared to Control. • Horses tended to refuse more proactively in the Dually, compared to Control. • Trained horses refused more proactively than Naïve horses in the Dually. • Stress and Horse Grimace Scores were not higher in Dually than Control. The Dually™ is a control headcollar designed to improve equine behaviour during handling challenges by applying greater pressure than a standard headcollar. Previous research indicated it did not improve compliance in naïve horses but did result in higher Horse Grimace Scale scores (HGS) indicative of discomfort. However, subjects had not been trained to step forward to release the pressure applied by the headcollar. The current study aimed to determine the effect of training on behaviour and physiology of horses wearing the Dually™ headcollar during handling challenges. To this end, subjects received three training sessions prior to completing two handling tests in which they crossed distinct novel obstacles, one wearing a Dually™ with a line attached to the pressure mechanism and one attached to the standard ring as a control. Behaviour was coded by hypothesis blind researchers: time to cross the obstacle and proactive refusal (moving away from the obstacle) were recorded as indicators of compliance and the Horse Grimace Scale was used to measure discomfort caused by each configuration of the device. Infrared thermography of ocular temperature, heart rate variability (RMSSD and low/high frequency ratios (LF/HF)) and salivary cortisol were measured as indicators of arousal. Data from the previous study on Naïve horses was also included to compare responses to the Dually in Naïve and Trained horses. Training resulted in a decrease in RMSSD (p = 0.002) and an increase in LF/HF (p = 0.012), compared to rest, indicating arousal. As per the original study, horses did not complete the tests more quickly in the Dually, compared to control (p = 0.698). Trained horses from this study tended to be more proactive in the Dually compared to Controls (p = 0.066) and significantly more so than Naïve horses from the previous study (p = 0.002) suggesting that behaviour becomes less desirable during early Dually training. Yet, stress and HGS indicators were not higher in the Dually compared to Control during testing. Results suggest the Dually has a negative effect on behaviour but not on stress or discomfort during short handling challenges. Further research is warranted to determine the long-term effect of Dually experience on behaviour and welfare. [ABSTRACT FROM AUTHOR]

• Dental disorders result in pain and modify the facial expression. • HGS is reliable for the identification of pain related to oral conditions. • Subjective pain evaluation, even by experienced veterinarians, is not reliable. • There is agreement between the HGS score determined in loco and using photographs. Dental disorders can cause discomfort and chronic pain, affecting the athletic performance and welfare of the horses. However, dental disorders may not be manifested with recognizable clinical signs and may, therefore, lead to late diagnosis or care. The present study aimed to evaluate the effect of dental disorders on equine welfare by analyzing the equine facial expression using the Horse Grimace Scale (HGS). Six different facial characteristics (ears held stiffly backwards, tension above the eye area, orbital tightening, prominently strained chewing muscle, mouth strained with pronounced chin, and strained nostrils with flattening of the profile) were evaluated in 33 adult horses, both males and females, that were regularly involved in sports or working activities. The animals had not received dental treatment for minimum 6 months and were evaluated using the HGS immediately before diagnosis and 15 days after undergoing odontological treatment. Initially, pain was scored in direct physical presence (in loco) by the investigator. At the same time, the horses' faces were photographed for further analysis by three evaluators trained in the use of horse grimace scale, and unaware of the study and condition of each animal. Additionally, four other equine veterinarians, not trained in the use of HGS, evaluated the same photographs subjectively, scoring 0 for no pain, 1 for mild pain, 2 for moderate pain, and 3 for severe pain, based on their professional experience. A significant agreement in the pain scores (p < 0.05) (Kappa test) was observed among all the evaluators who used the HGS (direct physical examination and from horses' photographs), with a strong and significant intra-class correlation coefficient (0.86; p < 0.05). However, there was no agreement among the veterinarian evaluators who used the subjective scale. In comparison with that before treatment, the pain score significantly decreased after dental treatment, as evaluated by the trained veterinarians (p < 0.05). While two of the subjective evaluators identified an improvement, the other two did not. In conclusion, dental disorders result in discomfort or pain and modify the facial expression of the horses. The HGS is reliable for the identification and quantification of pain associated with dental disorders either by face-to-face evaluation or by evaluation of photographs. However, these images are not suitable for subjective evaluation. [ABSTRACT FROM AUTHOR]