Damage to facial nerve can cause paralysis of nostril or tongueThe horse is highly susceptible to head injuries, partly because of the way its head and neck are constructed and also because of its athletic and emotional nature. For instance, an upset horse will fling up its head, increasing the risk of striking a stable door or the ceiling of a tunnel between paddock and racetrack. As many vital structures are located in the head, the injury's effects will be determined by the location and extent of the damage.
Simple injuries may include lacerations in which the skin and sometimes the underlying tissues are disrupted. If facial skin is cut or torn, suturing may be necessary to repair the damage. Skin over bony structures such as the face usually heals best if sutured, though many facial lacerations heal beautifully without stitches.
A blow to the face (such as a kick from another horse) can result in fracture of the facial bones over the sinuses, even though the skin may not be broken. The injury may heal improperly unless a veterinarian performs reconstructive surgery to realign the bones and prevent a depression in the facial contour. Fracture of the facial bones involving the sinuses can result in infection, requiring treatment with antibiotics.
The horse's ears are rarely injured because the horse usually tries to keep them out of harm's way. But occasionally an ear will be bitten by another horse, or caught in a fence and torn. Also, the ears of a sleeping horse (especially a foal) may be stepped on and damaged. Lacerations of the ear often can be sutured so the horse will not end up with a split or notched ear, but if damage occurs in the internal ear cartilage, the ear may heal in an abnormal shape.

Facial nerve injuries
The facial nerves that control the muscles for movement of nostrils, lips, eyelids, and ears are just under the skin, with one major nerve on each side of the face located along the cheek and over the back of the jaw. Any blow or laceration in the cheek area may cause temporary or permanent nerve damage.
If the major facial nerve is injured, the horse's face becomes partially or totally paralyzed on that side, with a drooping of the eyelid, drooping ear, and a hanging lower lip. The facial skin may also sag on that side. The eyelid remains about half closed and cannot blink in response to stimulation. Because of the droop in the lip and nostril on that one side, the muzzle appears twisted. The paralyzed side of the lip may hang down and expose the gums.
In severe cases of facial paralysis, the horse will find it difficult to eat and drink, or even breathe. The tongue may be partially paralyzed, which makes it hard to manipulate food and swallow. If part of the throat is paralyzed, the horse may have trouble breathing. If the nerve injury is higher and deeper than at the point where it crosses the jaw, the action of breathing itself may be impaired. The horse may be unable to control his nostrils, and the opening of the nostril may sag and collapse.
Which portions of the head and face are paralyzed will depend upon the level at which the injury occurred and which nerve branches are damaged. If the muscles of only the lips, nostrils, and cheeks are affected, the injury is probably on the superficial course of the nerve as it crosses the jaw. The facial nerve is fairly susceptible to injury at that point since it passes over the outside of the back of the jaw.
Facial paralysis due to pressure from a heavy bridle (or a poorly fitting bridle) or injury from a blow is not uncommon in horses. The nerves lie directly under the skin and are somewhat vulnerable to injury, and any severe blow to the head may damage the nerves at their main trunk where they leave the brain.
Chances for recovery from facial paralysis are poorest if the nerve is damaged high, such as where it leaves the brain. The most hopeful cases are those in which the paralysis is confined to just the lips and nostrils (with the damage low on the face).
The nerves run along the outside of the skull like thin electrical wires. Injury to a nerve leads to degeneration of some or all of the branches below it. It is like having an electrical wire cut: The impulses can no longer go through. Nerves may or may not regenerate, but it is a slow process; the wire-like fibers have to grow from the healthy nerve tissue above the injury, gradually regrowing to the muscles they serve.

Eye injuries
The horse's eye is also very susceptible to injury. Lacerations of the eyelid should be sutured. If a rip in the lower lid is not sutured so it can heal properly, tears will not be funneled into the tear duct and will run down the face. A torn upper lid will not be able to spread moisture over the eye, and the cornea will become damaged due to drying out.
The cornea is often injured or scratched by branches when the horse is going through trees and bushes, or by hay and bedding material. These small scratches can make the eye water and cause the horse to close the injured eye. These injuries should be treated as emergencies and seen by a veterinarian.
A more serious eye injury can result from corneal laceration, due to running into something. Some corneal lacerations can be successfully sutured. But a severe blow to the eye may result in blindness from detachment of the lens or retina or from internal bleeding within the eye itself.
A common head injury occurs when the horse rears over backward, as sometimes happens when a horse pulls back and breaks his halter or rope, or in a training accident. If a horse lands on his poll, a fracture may occur at the base of the brain, and possibly result in permanent damage or death. After hitting his head, the horse may be unable to stand, or may get up and stagger drunkenly. Other signs of severe head injury are bleeding from the nostrils or involuntary rapid eye movements.
A horse suffering from serious head injury needs immediate veterinary attention. If the skull has been injured or bruised, prompt treatment with DMSO given intravenously may keep the brain tissue from swelling and thus prevent serious and permanent impairment.