English
Facial nerve paralysis in horses refers to weakness or loss of movement in the muscles of the face. Depending on the location of the nerve damage, affected horses may develop a drooping ear or lip, an uneven muzzle, difficulty blinking, or problems keeping food in the mouth.
The condition can result from trauma or prolonged pressure on the nerve, but it can also occur with diseases affecting the skull, ear, or nervous system. Some cases are temporary, while others result in lasting facial weakness.
Facial nerve paralysis is particularly concerning when a horse cannot close an eye normally, since inadequate blinking leaves the surface of the eye vulnerable to injury. Facial paralysis accompanied by balance problems, difficulty swallowing, or other neurologic symptoms also warrants prompt veterinary investigation.
Keep reading to learn how to recognize facial nerve paralysis in horses, what can cause it, and how the condition is diagnosed, treated, and managed.
What Is Facial Nerve Paralysis in Horses?
Facial nerve paralysis occurs when damage to the facial nerve interferes with a horse’s ability to control the muscles of the face. The facial nerve, also known as cranial nerve VII, controls muscles involved in movement of the: [1][2]
- Ears
- Eyelids
- Nostrils
- Lips
- Other facial structures
The nerve also carries fibers involved in tear and saliva production and sensation in the tongue. [2] As a result, facial nerve damage can affect functions such as blinking and eating in addition to changing the appearance of the face. [1][2]
Facial nerve paralysis may affect one or both sides of the face and may involve the entire nerve or only individual branches. [1][2] The location and extent of the nerve damage determine which parts of the face are affected and the severity of the resulting symptoms. [1][2]
Complications of Facial Nerve Paralysis
Facial nerve paralysis can lead to serious complications involving the horse’s eyes and ability to eat and drink normally. [1][2]
Horses that cannot blink or completely close an eyelid are at increased risk of drying and injury on the surface of the eye. Reduced tear production increases this risk, and corneal ulcers may develop without adequate eye protection. [1][2][3][4]
Weakness of the lips and cheeks can make it difficult to grasp food and keep it in the mouth. Feed may collect between the teeth and cheek, while food or water may fall from the affected side of the mouth. [1][2][4][5]
Long-lasting nerve damage can cause loss of facial muscle mass and persistent facial asymmetry or weakness. [1][2][5]
What's your top priority with your horse's health?
What's your top priority with your horse's health?
Symptoms of Facial Nerve Paralysis in Horses
The symptoms of facial nerve paralysis depend on which part of the nerve is affected and whether the paralysis involves one or both sides of the face. With one-sided paralysis, facial asymmetry is often the most noticeable symptom. [1][2]
Common symptoms include: [1][2][3]
- Drooping of the ear
- Drooping of the eyelid
- Inability to blink normally
- Drooping of the lower lip
- Muzzle deviation toward the unaffected side
- Reduced movement or collapse of the nostril
- Dropping feed or difficulty keeping food in the mouth
- Drooling
Inability to close the eyelids normally is particularly important because it leaves the surface of the eye vulnerable to drying and injury. Reduced tear production can further increase the risk of corneal damage in some horses. [1][2][3]
Additional neurologic symptoms occur when facial paralysis is associated with disease affecting other nerves in the head or the central nervous system. These can include: [1][2]
- Head tilt
- Loss of balance
- Difficulty swallowing
- Tongue weakness
- Ataxia (incoordination)
When to Call the Veterinarian
Signs a horse requires prompt veterinary attention include: [1][2]
- Sudden facial weakness
- Sudden facial asymmetry
- Loss of balance
- Difficulty swallowing
- Worsening neurologic symptoms
- The inability to close the affected eye
A horse that cannot fully close the affected eye needs prompt veterinary attention because reduced blinking leaves the cornea exposed and increases the risk of drying, irritation, and ulceration. [2][4]
Causes of Facial Nerve Paralysis in Horses
Facial nerve paralysis develops when the facial nerve is damaged anywhere along its path from the brain to the muscles of the face. Trauma is one of the most common causes, but diseases affecting the skull, ear, and nervous system can also interfere with normal facial nerve function. The location and extent of the nerve damage influence which parts of the face are affected. [1][2]
When diagnostic testing does not identify trauma, infection, structural disease, or another underlying disorder, veterinarians describe the condition as idiopathic facial nerve paralysis. This diagnosis means that the cause remains unknown rather than confirming a specific disease process. [1][2]
Trauma & Pressure
The facial nerve is located relatively close to the surface along parts of the horse’s head, making it vulnerable to injury. Specific injuries that can damage the nerve include: [1][2][6]
- Head trauma
- Wounds
- Skull fractures
- Direct injury to the tissues surrounding the nerve
Trauma was the most commonly identified cause in a retrospective study of horses and other equids with facial nerve paralysis. [1][2][6]
Prolonged pressure can also injure the nerve even without an obvious wound. Pressure from a tightly fitted halter, prolonged restraint, or positioning of the head during general anesthesia can compress the nerve against underlying bone. [1][2][5]
The severity of paralysis depends on how badly the nerve is damaged. Mild compression may cause temporary weakness, while more severe trauma involving stretching, crushing, or disruption of the nerve can result in longer-lasting deficits. [1][2]
Temporohyoid Osteoarthropathy
Temporohyoid osteoarthropathy (THO) is a disorder involving the temporohyoid joint and nearby bones at the base of the skull. As the condition progresses, abnormal bone growth and thickening can make this normally flexible connection increasingly rigid. [4][7]
Loss of normal movement places greater stress on the surrounding bones, contributing to fractures near the skull. Because the facial and vestibulocochlear nerves pass through this region, these changes can damage one or both nerves. [4][7]
Horses with THO may show facial paralysis together with signs of balance dysfunction. Depending on which nerves are affected, additional signs may include: [4][7]
- Head tilt
- Loss of coordination
- Rapid abnormal eye movements (nystagmus)
- Difficulty maintaining balance
Neurologic & Other Diseases
Diseases affecting the brain, brainstem, or other parts of the nervous system can cause facial nerve paralysis. In these cases, the problem occurs closer to where the facial nerve originates rather than along the exposed portion of the nerve on the face. [1][2][8]
Horses with a central neurologic cause usually show other abnormalities in addition to facial weakness. These can include changes in: [1][2][8]
- Awareness
- Coordination
- Balance
- Swallowing
- Function of other cranial nerves
The presence of additional neurologic signs helps veterinarians determine whether the problem involves the facial nerve alone or reflects a more widespread nervous system disorder. [1][2][8]
Disease of the middle or inner ear is also a possible underlying cause because the nerve interacts closely with other structures in this region. [1][2]
Other reported causes include: [1][2]
- Guttural pouch disease
- Inflammation affecting the nerve
- Tumors involving nearby tissues or the nervous system
Congenital Causes
Rarely, horses are born with facial nerve dysfunction. Congenital cases have been associated with abnormal development or absence of portions of the facial nerve and typically become apparent in foals or young horses. [3][9]
Diagnosis
Diagnosing facial nerve paralysis involves localizing the site of nerve dysfunction and identifying the underlying cause. A veterinarian first evaluates the horse’s facial symmetry, ear and eyelid movement, lip position, nostril movement, ability to eat and drink, and other functions controlled by the facial nerve. [1][2]
A complete neurologic examination helps determine whether the problem affects only the facial nerve or involves the brain, brainstem, or other cranial nerves. [1][2][8]
The horse’s history provides additional clues. Veterinarians consider: [1][2]
- Recent head trauma
- Prolonged halter pressure
- Anesthesia
- Ear or guttural pouch disease
- Whether the facial weakness developed suddenly or gradually
Depending on the suspected cause, diagnostic tests may include: [1][2][4][6]
- Radiographs (X-rays)
- CT
- MRI
- Guttural pouch endoscopy
- Cerebrospinal fluid analysis (“spinal tap”)
X-rays help veterinarians look for skull fractures, bony abnormalities, and changes around the temporohyoid region. However, overlapping structures in the horse’s skull can make some abnormalities difficult to see clearly on standard radiographs. [2][4][6][7]
Computed tomography (CT) provides more detailed images of the skull and surrounding structures. This type of imaging is useful when veterinarians suspect temporohyoid osteoarthropathy, fractures, or other bony changes close to the facial nerve. CT can also help identify abnormalities that standard X-rays do not show clearly. [1][2][4][7]
Veterinarians use magnetic resonance imaging (MRI) when they suspect disease involving the brain, cranial nerves, or other structures that are difficult to evaluate with radiographs or CT alone. [2]
Guttural pouch endoscopy allows direct examination of structures near the temporohyoid joint and helps identify abnormalities associated with guttural pouch disease or temporohyoid osteoarthropathy. [2][4][7]
When the examination suggests disease of the brain or central nervous system, veterinarians may collect cerebrospinal fluid for laboratory analysis. Changes in this fluid can provide evidence of inflammation or other neurologic disease and help distinguish a central problem from damage affecting the facial nerve. [1][2][8]
Treatment
While the veterinarian is investigating the cause of a horse’s facial paralysis, management may include: [1][2]
- Protecting an eye that cannot close completely
- Monitoring for redness, discharge, cloudiness, or other eye changes
- Checking that the horse can eat and drink normally
- Monitoring for head tilt, loss of balance, difficulty swallowing, or worsening facial weakness
- Removing or loosening equipment that may be placing pressure on the side of the head
Treatment depends on the underlying cause and severity of the nerve damage. When facial paralysis results from another condition, such as temporohyoid osteoarthropathy or neurologic disease, treatment focuses on managing that condition. [1][2][4]
Protecting an eye that cannot close normally is an important part of treatment. Lubricating eye medications may be used to prevent drying and corneal injury, while existing ulcers or other eye problems require appropriate treatment. [2][4]
Supportive care may also be necessary when facial weakness interferes with eating or drinking. [2][5] Treatment of the nerve itself is limited, and recovery largely depends on the cause and extent of the damage. [1][2]
Recovery & Prognosis
Recovery from facial nerve paralysis depends on the cause, location, and severity of nerve damage. Some horses regain normal facial movement, and others have persistent weakness or recover only part of their normal facial function. [1][2]
Improvement may occur gradually as the nerve heals. The outlook also depends on whether the underlying condition is treatable. Horses with temporohyoid osteoarthropathy may continue to have some facial weakness even after treatment, although many return to athletic use. [1][2][4]
Persistent facial paralysis may require ongoing management, particularly when the horse cannot fully close the affected eye. [2][4]
Preventing Facial Nerve Injury
Not all causes of facial nerve paralysis can be prevented. However, reducing unnecessary pressure and trauma around the head may lower the risk of some facial nerve injuries. [2][5]
Preventive measures include: [2][5]
- Ensuring halters and other headgear fit correctly
- Avoiding prolonged pressure from halters or other equipment
- Providing appropriate padding and positioning during anesthesia and prolonged recumbency
- Addressing head injuries promptly
- Seeking veterinary assessment for new facial, balance, or other neurologic symptoms
Prompt veterinary examination of new facial asymmetry or neurologic signs may help identify underlying conditions before complications develop.
Conditions such as temporohyoid osteoarthropathy and other neurologic diseases are not always preventable. Early recognition and treatment may reduce the risk of complications, including fractures and corneal injury. [2][4]
Frequently Asked Questions
Here are some frequently asked questions about facial nerve paralysis in horses:
Facial nerve paralysis in horses occurs when damage to the facial nerve disrupts control of the facial muscles. This nerve controls movement of the ears, eyelids, nostrils, lips, and other facial structures. Damage can also interfere with tear production, saliva production, eating, and blinking.
Facial nerve paralysis in horses can be caused by head trauma, wounds, fractures, or prolonged pressure on the nerve. Pressure from a halter or positioning of the head during general anesthesia can also cause nerve damage. Other possible causes include temporohyoid osteoarthropathy, middle or inner ear disease, guttural pouch disease, nerve inflammation, tumors, and diseases affecting the brain or nervous system. In some cases, no underlying cause can be identified.
Symptoms of facial nerve paralysis in horses can include a drooping ear, eyelid, or lower lip, an uneven muzzle, and reduced movement or collapse of one nostril. An affected horse may be unable to blink normally and may drool, drop feed, or have difficulty keeping food in its mouth. Head tilt, loss of balance, difficulty swallowing, tongue weakness, or poor coordination may occur if other nerves or the central nervous system are also affected.
Facial nerve paralysis can affect one or both sides of a horse's face. One-sided paralysis typically causes noticeable facial asymmetry, such as muzzle deviation toward the unaffected side. The pattern and severity of signs depend on the location of the nerve damage and whether the entire nerve or only individual branches are involved.
Facial nerve paralysis in horses requires prompt veterinary assessment, especially when it develops suddenly. Inability to close an eye, difficulty swallowing, head tilt, loss of balance, poor coordination, or worsening neurologic signs require urgent attention. These signs can indicate involvement of other nerves or the central nervous system and may increase the risk of serious complications.
Facial nerve paralysis can damage a horse's eye when the affected eyelid cannot blink or close completely. Exposure can cause the surface of the eye to dry out and become injured, while reduced tear production may increase the risk of corneal ulcers. Redness, discharge, cloudiness, or other eye changes require prompt veterinary attention. The eye may need ongoing protection if normal eyelid function does not return.
A horse with facial nerve paralysis may still eat and drink, but weakness of the lips and cheeks can make these activities difficult. Feed may fall from the mouth or collect between the teeth and cheek, and water may escape from the affected side. The horse's intake should be monitored closely, and supportive care may be needed. Difficulty swallowing requires prompt veterinary assessment because it may indicate that other nerves or the central nervous system are involved.
Facial nerve paralysis in horses is diagnosed by evaluating the pattern of facial weakness, locating the likely area of nerve damage, and investigating the underlying cause. A veterinarian will also look for balance problems, swallowing difficulty, poor coordination, or other signs that additional nerves or the brain may be affected. Depending on the findings, diagnostic testing may include imaging, guttural pouch endoscopy, or analysis of cerebrospinal fluid.
Facial nerve paralysis in horses is treated according to its underlying cause and the severity of the nerve damage. Treatment may focus on managing conditions such as temporohyoid osteoarthropathy, ear disease, or neurologic disease. An eye that cannot close may require lubricating medication and protection from drying or injury, while horses having trouble eating or drinking may need supportive care. Treatment options for the damaged nerve itself are limited.
A horse can recover from facial nerve paralysis, but the outcome depends on the cause, location, and severity of the nerve damage. Some horses regain normal facial movement, while others recover only partially or remain permanently weak. The prognosis also depends on whether the underlying condition can be treated successfully.
How long facial nerve paralysis takes to heal in horses varies considerably because recovery depends on the type and extent of the damage. Improvement may occur gradually as the nerve heals, but a specific recovery period cannot be predicted from facial signs alone. Some horses are left with lasting facial asymmetry or weakness and require ongoing management.
A horse with temporohyoid osteoarthropathy may recover some facial function after the underlying condition is treated, but weakness can persist. This condition can damage the facial nerve and may also affect nerves involved in balance. Even when some facial weakness remains, many treated horses can return to athletic use.
If a horse suddenly develops facial weakness, contact a veterinarian promptly for an assessment. Check whether the horse can close both eyes, eat, drink, and swallow normally, and watch for head tilt, loss of balance, poor coordination, or worsening weakness. Equipment placing pressure on the side of the head should be loosened or removed while veterinary guidance is sought. An eye that cannot close completely needs prompt protection to reduce the risk of corneal injury.
Some cases of facial nerve paralysis in horses may be prevented by reducing unnecessary pressure and trauma around the head. Halters and other headgear should fit correctly and should not place prolonged pressure over the nerve. Appropriate padding and positioning during anesthesia or prolonged recumbency may also lower the risk of pressure-related injury. Diseases such as temporohyoid osteoarthropathy cannot always be prevented, making early recognition and veterinary care important.
Summary
Facial nerve paralysis affects a horse's facial movement and may interfere with blinking, eating, and drinking. Prompt veterinary care is important when the eye cannot close or other neurologic signs occur.
- Signs include a drooping ear, eyelid, or lip; muzzle deviation; drooling; and difficulty retaining food
- Causes include trauma, prolonged pressure, temporohyoid osteoarthropathy, ear disease, and neurologic disorders
- Impaired blinking and reduced tear production can lead to corneal drying, injury, and ulceration
- Diagnosis may involve a neurologic examination, imaging, endoscopy, or cerebrospinal fluid analysis
- Treatment focuses on the underlying cause, eye protection, and support for eating or drinking difficulties
- Recovery depends on the severity of nerve damage, and some horses have persistent facial weakness
References
- Boorman. S. et al. Facial Nerve Paralysis in 64 Equids: Clinical Variables, Diagnosis, and Outcome. Journal of Veterinary Internal Medicine. 2020.
- Furr. M. and Reed. S. Equine Neurology. Wiley. 2015.
- Russell. C. K. et al. Congenital Facial Nerve Dysfunction. Equine Veterinary Education. 2019.
- Walker. A. M. et al. Temporohyoid Osteoarthropathy in 33 Horses (1993–2000). Journal of Veterinary Internal Medicine. 2002.
- de Fourmestraux. C. et al. Multimodal Therapy Including Electroacupuncture for the Treatment of Facial Nerve Paralysis in a Horse. Equine Veterinary Education. 2014.
- Auer. J. Ed. Equine Surgery. Elsevier. 2019.
- Divers. T. J. et al. Temporohyoid Osteoarthropathy. Clinical Techniques in Equine Practice. 2006.
- Reed. S. M. Ed. Equine Internal Medicine. Elsevier. 2018.
- Schön. S. et al. Congenital Unilateral Facial Nerve Paralysis in a Warmblood Filly. Equine Veterinary Education. 2019.
