How Can You Tell if a Horse Is in Pain? Horse Grimace Scale Explained

By Dr Duncan Houston

Horses do not always display pain in the dramatic way owners expect.

A horse with significant discomfort may stand quietly, eat a few mouthfuls or suddenly appear brighter when someone walks into the stable. In some cases, the first clues are subtle changes around the ears, eyes, muzzle and jaw.

The Horse Grimace Scale gives owners and veterinarians a structured way to recognise these facial changes. It can be extremely useful, but it is not a magic pain detector and it cannot tell you what is causing the pain.

Quick Answer

The Horse Grimace Scale assesses six pain-associated facial features. Each feature is scored from 0 to 2, producing a total score between 0 and 12.

A higher or rising score can indicate that a horse is experiencing pain, particularly when several facial changes appear together. However, there is no universal score that proves a horse is safe, painful or experiencing an emergency. The facial score must be interpreted alongside the horse’s behaviour, posture, movement, appetite, manure, vital signs and clinical examination. Current expert consensus is that no single assessment method can fully capture the multidimensional nature of equine pain. (PLOS)

What Is the Horse Grimace Scale?

The Horse Grimace Scale, commonly shortened to HGS, is a structured facial-expression scoring system developed to help identify pain in horses.

The original study involved:

• 40 stallions undergoing routine castration

• Two different flunixin analgesia protocols

• Six additional horses undergoing general anaesthesia without painful surgery

• 126 photographs taken before and after the procedures

• Five blinded observers scoring the horses’ facial expressions

Horses undergoing castration had significantly higher HGS scores eight hours after surgery than they had before surgery. The anaesthesia-only control horses did not show the same increase.

The total HGS showed excellent agreement between observers, with an intraclass correlation coefficient of 0.92. By comparison, the observers’ unstructured judgement of whether a horse appeared painful was only approximately 73% accurate. This suggests that a defined scoring system may be more reliable than simply glancing at a horse and deciding that they “look a bit sore.” (PLOS)

What Are the Six Horse Grimace Scale Signs?

The HGS evaluates six facial action units. These are visible changes produced by tension or positioning of particular facial structures.

Each feature must be judged in context. One ear moving backwards or one brief squint does not establish that a horse is painful.

1. Stiffly Backward Ears

The ears are held rigidly backwards rather than moving freely towards sounds.

The space between the ears may also appear wider than normal.

This is different from a horse briefly directing both ears towards something behind them. Pain-associated ear position tends to be:

• More fixed

• Less responsive to surrounding sounds

• Accompanied by tension elsewhere in the face

• Persistent across repeated observations

Pinned ears can also occur with aggression, fear, social conflict or irritation. Ear position should therefore never be interpreted by itself.

2. Orbital Tightening

Orbital tightening means narrowing or partial closure of the eyelids.

The visible portion of the eye becomes smaller, and the horse may appear to be squinting.

This can be one of the clearer pain-associated changes, but similar appearances may occur when a horse is:

• Sleeping or drowsy

• Standing in bright sunlight

• Sedated

• Experiencing primary eye disease

• Being irritated by flies, dust or wind

A horse holding one eye more tightly closed than the other may have a painful eye rather than generalised pain.

3. Tension Above the Eye

Muscle contraction above the eye produces a more angular, hollowed or furrowed appearance.

The underlying bone may become more visible, and the area above the eye can look tense rather than smoothly rounded.

This feature may be difficult to assess in horses with:

• A thick winter coat

• Long forelock hair

• Deeply set eyes

• Strong facial conformation

• Poor lighting

Comparison with a photograph of the same horse when comfortable is particularly valuable.

4. Prominent, Strained Chewing Muscles

The masseter or chewing muscles become tense and more visibly defined.

The side of the face may appear harder or more angular, particularly above and behind the corner of the mouth.

Do not score this feature while the horse is actively chewing forage or concentrate. Wait until the jaw is resting.

Jaw tension may also occur with dental pain, bit discomfort, anxiety or frustration.

5. Strained Mouth and Pronounced Chin

The lips appear tense rather than soft.

The upper lip may be drawn backwards while the lower lip and chin become more prominent. The horse may lose the relaxed, rounded appearance normally seen around the muzzle.

This must be distinguished from:

• Flehmen

• Licking or chewing

• Food anticipation

• Mouthing a bit

• Investigating an odour

• Temporary lip movement after sedation

6. Strained Nostrils and Flattened Facial Profile

The nostrils may become tense, elongated or slightly dilated. The natural curves between the nostrils, lips and muzzle may appear flatter or more rigid.

This was the least consistently scored feature in the original HGS study, with lower observer agreement than the other facial units. Recent exercise, heat, respiratory effort, excitement and fear can all alter nostril shape, so it is particularly important not to use this feature alone. (PLOS)

Horse Grimace Scale Scoring

Each facial action unit receives one of three scores:

Score	Meaning
0	The feature is not present
1	The feature is moderately present
2	The feature is obviously present

The six scores are added together, creating a possible total between 0 and 12. (PLOS)

Example

A horse might receive:

Facial feature	Score
Stiffly backward ears	2
Orbital tightening	1
Tension above the eye	1
Strained chewing muscles	1
Strained mouth and chin	1
Strained nostrils	0
Total	6 out of 12

This result would justify a closer assessment, particularly if it represented a clear change from the horse’s normal face.

It would not tell you whether the horse had colic, laminitis, dental disease or postoperative pain.

What if You Cannot See a Feature Clearly?

Do not guess.

Record that feature as unable to assess, then obtain another photograph or observe the horse from another angle.

A poor-quality image can create a very confident but entirely fictional pain score, which is not quite the clinical breakthrough anyone was hoping for.

What Horse Grimace Score Means the Horse Is in Pain?

There is no universally validated HGS cutoff that applies to every horse and every condition.

In one study of horses with colic, a score above 6 out of 12 identified painful horses with 100% sensitivity and 79% specificity. However, this cutoff came from a particular colic population and should not automatically be applied to laminitis, eye pain, dental disease, postoperative cases or horses at home. (Beva Online Library)

A total score is most useful when:

• Compared with the same horse’s normal baseline

• Repeated under similar conditions

• Interpreted alongside behaviour and physical findings

• Used to monitor change over time

• Assessed before and after veterinarian-directed analgesia

A score rising from 1 to 5 in the same horse may be more clinically meaningful than a single score of 5 in a horse whose normal facial expression is unknown.

What Does the Research Show?

The HGS has been investigated in several painful conditions, but its effectiveness is not identical across all diseases.

Pain Following Castration

The original study showed that HGS scores increased significantly after routine surgical castration but not after anaesthesia alone.

The structured HGS score also had stronger agreement between observers than their unaided judgement of whether the photographs appeared painful. This supported its use as an objective method for identifying acute postoperative discomfort. (PLOS)

Acute Laminitis

A later study assessed 10 untreated horses with acute laminitis when they were admitted and again seven days after treatment began.

Higher HGS scores were associated with greater clinical pain severity and higher Obel laminitis grades. Scores obtained from short videos were similar to those obtained from still photographs, suggesting that the facial scale may be used without forcing a painful horse to walk solely for assessment.

The study was small, so the findings were promising rather than definitive. (MDPI)

Colic

Research comparing the HGS with composite pain scales in horses with colic found good observer reliability. In the study population, a score above 6 out of 12 performed reasonably well in identifying pain.

However, a facial score cannot determine:

• Which part of the gastrointestinal tract is affected

• Whether the intestine is obstructed or displaced

• Whether the horse requires surgery

• Whether pain relief has temporarily masked a serious lesion

A horse with colic signs still requires clinical examination regardless of the facial score. (Beva Online Library)

Dental Pain

A study of 33 adult horses found that HGS scores decreased after treatment of dental disorders. Trained observers showed strong agreement, while veterinarians using only subjective impressions were less consistent. (ScienceDirect)

However, a later preliminary study of horses with conditions such as equine odontoclastic tooth resorption and hypercementosis reported poor agreement between observers. The study was small, but it highlights that chronic dental pain may not always produce a clear, consistently recognised grimace. (BVA Journals)

Gastric Ulcers

The HGS did not distinguish horses with and without equine gastric ulcer syndrome in a study of 61 horses. Scores also did not increase consistently with ulcer severity.

This means that a low HGS score cannot rule out gastric ulcers, and a high score cannot diagnose them. Gastroscopy and clinical assessment remain necessary when gastric disease is suspected. (Animal Welfare Institute)

What Is the Overall Verdict?

The strongest evidence supports using the HGS as an adjunct for detecting and monitoring some forms of acute pain.

It is less reliable as a universal test for chronic, subtle or internally located conditions. The current international consensus on equine pain assessment concludes that no single tool adequately captures every aspect of pain. The Equine Pain Scale, which combines several behavioural and clinical elements, was identified as a particularly practical option for routine clinical use. (Beva Online Library)

The HGS remains valuable, but it should be one part of the assessment rather than the entire assessment.

Why Can the Horse Grimace Scale Be Misleading?

A horse’s face changes for reasons other than pain.

Stress and Social Isolation

A 2025 study examined facial activity during mild nociceptive stimulation, social isolation, sedation and combinations of these conditions.

Social isolation produced facial changes that could obscure the distinction between isolation and pain. When the painful stimulus occurred during isolation, facial activity could not reliably separate the combined experience from isolation alone. (Nature)

A horse that has just been separated from a companion, transported or introduced to a new environment may therefore produce facial changes reflecting stress and arousal rather than pain alone.

Sedation

Sedation can reduce or alter facial-muscle activity.

In the same study, the combination of sedation and a nociceptive stimulus could not be reliably distinguished from the control state through facial activity alone. This suggests that a recently sedated horse may still be painful while displaying a relatively low facial score. (Nature)

Where practical, obtain a baseline assessment before sedation. After sedation, rely more heavily on the clinical examination, diagnosis, expected procedure-related pain and veterinarian-directed analgesia.

Human Presence

Horses may temporarily suppress discomfort behaviour when someone approaches.

In a study of 20 hospitalised orthopaedic surgery patients, observable discomfort behaviours decreased by an average of approximately 77% while a caretaker was present. In 30% of the horses, the ongoing discomfort behaviour stopped entirely during the visit and resumed after the person left. (MDPI)

This is one reason that remote observation and stable-camera footage can be so valuable.

A horse that looks better when you walk in may simply be paying attention to you.

Sleep and Drowsiness

A resting horse may show:

• Partially closed eyes

• Reduced facial movement

• Lowered head position

• Relaxed ears

• A drooping lower lip

These should not be mistaken automatically for pain.

The difference is usually found in the whole pattern. A resting horse should appear physically relaxed and return to normal awareness when appropriately disturbed. A painful horse may remain tense, withdrawn, reluctant to move or uninterested in food.

Exercise, Heat and Respiratory Effort

Exercise can cause:

• Dilated nostrils

• Tight facial muscles

• Increased breathing

• Ear fixation

• Sweating

• Temporary fatigue

Do not calculate an HGS score immediately after strenuous exercise and interpret it as resting pain.

Allow the horse to recover, then reassess. Abnormal recovery, persistent breathing difficulty or continuing facial tension still deserves investigation.

Individual Facial Conformation

Breed, age, facial shape, muscle development, coat colour and lighting can affect how the facial units appear.

A deeply set eye may naturally produce more visible tension above the orbit. A horse with large chewing muscles may appear more tense than a finer-headed horse.

This makes individual baseline photographs considerably more useful than trying to compare every horse with one idealised image.

Can Owners Use the Horse Grimace Scale?

Yes, but it should be used as an early-warning and monitoring tool rather than a home diagnostic test.

The HGS can help owners:

• Identify that something has changed

• Communicate observations more clearly

• Monitor recovery following treatment

• Compare the horse before and after an intervention

• Decide that veterinary advice is needed

• Detect pain that may otherwise be dismissed as quiet behaviour

It cannot tell an owner:

• What disease is present

• How much medication to give

• Whether colic requires surgery

• Whether an eye condition threatens vision

• Whether a lame horse has a tendon, joint or hoof lesion

• Whether it is safe to continue exercise

How to Assess Your Horse’s Face Properly

1. Establish a Normal Baseline

Take photographs or short videos of your horse when they are:

• Healthy

• Comfortable

• Resting quietly

• Not eating

• Not immediately after exercise

• Not sedated

• In familiar surroundings

Capture:

• A front view

• Both side views

• A three-quarter view

These images give you a reference for the horse’s usual ear, eye, jaw, lip and nostril position.

2. Observe the Horse From a Distance

Watch the horse undisturbed for at least one or two minutes before approaching.

Look for:

• Normal eating

• Interest in the surroundings

• Weight shifting

• Pawing

• Flank-watching

• Repeated lying down

• Reluctance to move

• Abnormal posture

• Interaction with other horses

• Breathing effort

Remote video may reveal more than standing directly in front of the horse.

3. Choose a Neutral Moment

Avoid scoring while the horse is:

• Chewing

• Calling

• Sniffing urine

• Performing flehmen

• Reacting to flies

• Recently exercised

• Being separated from another horse

• Being handled for a painful procedure

• Deeply drowsy

• Under the influence of sedation

These situations can change several facial units without giving a clean measure of pain.

4. Score All Six Features

Score each visible feature from 0 to 2.

Do not allow one dramatic sign to determine the entire result. A horse with ears back but relaxed eyes, jaw, muzzle and behaviour may not be showing a pain grimace.

The scale becomes more persuasive when several independent features change together.

5. Assess the Rest of the Horse

The face should be combined with:

• Appetite

• Water intake

• Manure production

• Urination

• Rectal temperature

• Heart rate

• Respiratory rate and effort

• Gum colour and moisture

• Gait

• Willingness to turn

• Digital pulses

• Limb swelling

• Wounds or surgical sites

• Eye comfort

• Response to touch

A facial score without functional information is incomplete.

6. Repeat the Assessment

Repeat the score under similar conditions.

Useful comparisons include:

• Before and after prescribed pain relief

• Morning and evening

• Before and after a bandage change

• Before and after dental treatment

• Before and after a veterinarian-directed rehabilitation session

• At consistent intervals after surgery

Record the time of medication because a low score shortly after analgesia and a rapidly rising score before the next dose have different implications.

7. Record a Video

A 30- to 60-second video can show:

• Whether the facial changes persist

• Ear movement

• Blinking

• Jaw tension

• Breathing

• Weight shifting

• Interaction with the environment

Video is often more useful than one perfectly timed photograph that captures the horse halfway through a blink.

What Can a Painful Face Mean?

The HGS identifies that pain may be present. It does not identify the source.

Facial changes combined with	More important possibilities
Pawing, flank-watching, lying down or reduced manure	Colic or gastrointestinal pain
Reluctance to walk or turn, weight shifting and stronger digital pulses	Laminitis or hoof pain
Squinting, tearing, redness or eye cloudiness	Corneal ulcer, uveitis or another painful eye condition
Quidding, slow chewing, dropping feed or facial swelling	Dental or oral disease
Lameness, swelling or reluctance to bear weight	Musculoskeletal or hoof injury
Worsening pain after surgery	Inadequate analgesia or a postoperative complication
Head-shaking, ear sensitivity or difficulty chewing	Ear, dental, hyoid, neurological or head-related pain
Fever, lethargy and reduced appetite	Infection or systemic illness

The face tells you to look more closely. The remainder of the horse helps determine where to look.

Horse Pain Risk Framework

Do not classify urgency from the HGS number alone.

Lower Immediate Concern

The horse has:

• One mild or transient facial change

• Normal appetite and water intake

• Normal manure

• Normal movement

• No swelling, fever or obvious pain

• A clear non-painful explanation such as brief drowsiness or attention

• A face that returns to baseline within a short period

Action: Continue monitoring and repeat the assessment when the horse is undisturbed.

Moderate Concern

The horse has:

• Several facial units scored as moderately present

• A persistent change from their normal appearance

• Reduced interest in food

• Mild stiffness or reluctance to move

• Increased repetitive behaviour

• A recent procedure, injury or management change

• A score that continues rising

Action: Contact your veterinarian for advice that day, particularly if the change is new or has persisted for several hours.

High Concern

The horse has:

• Several obvious facial pain features

• Significant lameness

• Repeated weight shifting

• Colic behaviour

• Reduced or absent manure

• Eye pain

• Marked swelling

• Progressive postoperative pain

• Fever or depression

• Pain that returns despite prescribed medication

Action: Arrange urgent veterinary assessment. Do not wait for the score to become higher.

Critical

The horse has:

• Repeated or violent rolling

• Collapse

• Severe breathing difficulty

• Incoordination or seizures

• Non-weight-bearing lameness

• Acute laminitis signs

• A severely painful or injured eye

• Uncontrolled haemorrhage

• Severe pain that does not respond to prescribed treatment

• Abnormal awareness or inability to stand safely

Action: Treat this as an emergency regardless of the facial score.

When Is This an Emergency?

Call a veterinarian immediately if facial signs of pain occur with any of the following.

Colic Signs

• Pawing

• Flank-watching

• Kicking at the abdomen

• Repeated lying down or rolling

• Sweating without exercise

• Loss of appetite

• Reduced or absent manure

• Abdominal distension

• Rapidly worsening restlessness or depression

Clinical signs can identify abdominal pain, but they cannot tell you which part of the gastrointestinal tract is affected or whether surgery will be required. (Horse Report)

Laminitis Signs

• Reluctance to walk

• Difficulty turning

• Repeated weight shifting

• Strong or bounding digital pulses

• A shortened or stilted gait

• A rocked-back stance

• Pain affecting more than one foot

Suspected laminitis requires immediate veterinary advice. Do not repeatedly force the horse to walk or circle to demonstrate the problem. (AAEP)

Eye Pain

• Squinting

• Excessive tearing

• A cloudy or blue appearance

• Redness

• Eyelid swelling

• Eye trauma

• An abnormal pupil

• Sudden visual difficulty

Painful eyes in horses are emergencies because corneal ulcers, uveitis, glaucoma, stromal abscesses and trauma can progress rapidly and threaten vision. (MSD Veterinary Manual)

Severe Lameness or Neurological Signs

• Refusal to bear weight

• An abnormal limb angle

• Falling

• Incoordination

• Circling

• Head pressing

• Seizures

• Collapse

• Sudden apparent blindness

These signs require urgent veterinary assessment rather than further facial scoring.

What Should You Do Right Now?

1. Stop Exercise

Do not continue riding, lunging or training a horse showing a new pain face.

Exercise may worsen the underlying injury and can make subsequent assessment more difficult.

2. Observe From a Safe Distance

Watch the horse before handling them.

A painful horse may kick, strike, bite or move suddenly without directing deliberate aggression towards the handler.

3. Record the Face and Whole Body

Take a short video showing:

• The face

• Overall posture

• Breathing

• Movement

• The affected limb or body area

• Any wound or swelling

Do not focus so closely on the muzzle that the horse’s severe weight shifting is edited out of the medical evidence.

4. Check Basic Clinical Information

When safe, record:

• Temperature

• Heart rate

• Respiratory rate

• Gum colour

• Appetite

• Water intake

• Manure

• Urination

• Digital pulses

• Recent medication

Send this information with the video when contacting your veterinarian.

5. Make the Horse Safe and Comfortable

Depending on the suspected problem:

• Keep the horse in a safe, quiet area

• Use deep supportive bedding when hoof pain is suspected

• Remove hazards around a horse showing colic signs

• Keep a painful eye out of bright light where practical

• Avoid unnecessary transport until veterinary advice is obtained

• Prevent the horse from being chased by herd mates

Do not force movement merely to test whether the horse is still painful.

6. Do Not Give Additional Medication Without Advice

Do not administer:

• Human painkillers

• Leftover sedatives

• Additional phenylbutazone or flunixin

• Steroid eye drops

• Someone else’s prescription medication

• Multiple anti-inflammatory drugs together

Medication can cause toxicity, mask important signs or worsen certain conditions.

Tell the veterinarian exactly what has already been given, including dose and time.

7. Do Not Wait for a Particular Number

A horse does not have to reach 7 out of 12 before receiving help.

A horse with a score of 3 and a penetrating eye injury needs urgent treatment. A horse with a score of 2 and severe non-weight-bearing lameness needs urgent treatment. A sedated horse with a low score may still be significantly painful.

Treat the horse, not the spreadsheet.

Common Horse Grimace Scale Mistakes

Scoring a Single Feature

Ears held back do not automatically mean pain. The value of the HGS comes from examining several facial regions together.

Scoring While the Horse Is Eating

Chewing changes the jaw, mouth and nostrils and can falsely increase several scores.

Confusing Sleep With Pain

Partially closed eyes and a low head can occur during normal rest. Look for muscular relaxation, normal breathing and an appropriate response when the horse becomes alert.

Scoring Immediately After Exercise

Nostril dilation, facial tension, sweating and fatigue can reflect exertion rather than underlying pain.

Ignoring Sedation

Sedation may conceal facial expressions and reduce the apparent score even when nociception remains present. (Nature)

Using the Scale to Diagnose a Disease

The HGS does not diagnose colic, gastric ulcers, laminitis, dental disease or eye disease.

It identifies a pattern that may be consistent with pain.

Assuming a Low Score Rules Out Pain

Chronic pain, gastric disease, subtle lameness and sedated patients may not develop a dramatic grimace. Horses may also suppress visible discomfort when a person approaches. (Animal Welfare Institute)

Giving Medication to Improve the Number

The purpose of a pain score is to support appropriate treatment, not to chase a prettier number without understanding the cause.

How Can Pain Monitoring Be Improved?

Create a Baseline Library

Keep clear photographs and short videos of the horse when comfortable.

Include:

• Resting face

• Normal walk and turns

• Normal posture

• Normal eye appearance

• Normal breathing

Use Consistent Conditions

Whenever possible, use:

• Similar lighting

• Similar camera angle

• Similar distance

• The same time relative to medication

• A quiet environment

• The same observer

Monitor Function as Well as Expression

Track whether the horse can:

• Eat

• Drink

• Pass manure

• Walk

• Turn

• Lie down and rise

• Interact normally

• Rest

• Respond to the environment

Functional deterioration may be more important than a small change in the numerical score.

Use Remote Observation

A stable camera can reveal pain behaviours that disappear when people enter.

This is particularly valuable after surgery, during colic monitoring and when assessing a withdrawn or unusually quiet horse. (MDPI)

Train Everyone Using the Same Method

Owners, grooms and staff should use the same six facial units and scoring definitions.

The message “he looks miserable” is worth investigating. The message “his orbital tightening, stiff ear position and mouth tension have all increased since 2 pm” is considerably easier to act upon.

Frequently Asked Questions

What Horse Grimace Scale score indicates pain?

There is no universal cutoff for every condition. A score above 6 out of 12 performed well in one colic study, but this should not be applied blindly to all horses or diseases. Trends, clinical signs and the individual horse’s baseline matter more. (Beva Online Library)

Can a horse be in pain with a low HGS score?

Yes. Sedation, stress, chronic disease, individual variation and the presence of a person can reduce or obscure visible pain behaviour. A low score does not overrule obvious clinical signs. (Nature)

Can owners use the Horse Grimace Scale?

Yes. Owners can use it as an early-warning and monitoring tool, particularly when they know the horse’s normal expression. It should not replace veterinary diagnosis or determine medication doses.

Can photographs be used instead of watching the horse live?

Yes. The original scale was developed from photographs, and a small laminitis study found similar results using still images and short videos. Images must be clear, well lit and taken while the horse is not chewing or reacting to another stimulus. (PLOS)

Can the HGS diagnose gastric ulcers?

No. A study involving 61 horses found no significant difference in HGS scores between horses with and without gastric lesions, and scores did not correspond reliably with ulcer severity. (Animal Welfare Institute)

Final Thoughts

The Horse Grimace Scale is an important advance in equine pain recognition.

It takes small changes in the ears, eyes, jaw, lips and nostrils and turns them into a repeatable framework. That can help owners notice pain earlier, describe it more clearly and monitor whether a horse is improving.

Its greatest limitation is also simple: a face is only one part of a horse.

Stress can resemble pain. Sedation can hide pain. Chronic conditions may produce little facial change, and horses may temporarily suppress discomfort when a person approaches. The latest expert consensus therefore supports multidimensional assessment rather than depending on one facial or behavioural tool.

Use the HGS as a warning light, not a final diagnosis.

When several facial changes appear together, compare them with the horse’s normal expression, assess the entire horse and consider what else has changed. When facial tension occurs with colic, laminitis, eye pain, severe lameness, neurological abnormalities or progressive postoperative discomfort, do not wait for another photograph.

---

ASK A VET™ can help you organise facial photographs, pain scores, medication times, movement videos and changes in appetite, manure or behaviour so that patterns can be reviewed more clearly. A horse with severe pain, colic, eye disease, laminitis signs or neurological abnormalities still requires direct veterinary examination.