The sporting use of the horse requires of course the integrity of its locomotor apparatus, bones and joints, muscles, and tendons, but also what controls and harmonizes their movements, i.e., the nervous system. The affections of the nervous system are very numerous in the horse, as in the other species. They can affect the peripheral nervous system (nerves) or the central nervous system (spinal cord and brain).
Traumatic affections in the horse
The horse can present central nervous disorders after traumas of different natures (when boarding a van or a truck with trauma to the neck when the head is raised untimely, during sharp reactions during the installation of the harness, during various falls during sporting events or during a traffic accident during transport). Symptoms vary from decreased alertness to decubitus and coma. Superficial peripheral nerves can be injured by compression along their path. This is the case with facial paralysis or supra-scapular nerve paralysis after prolonged lateral decubitus (e.g., during long general anesthesia). In many cases, the condition is reversible if treatment is initiated early enough. These treatments involve the administration of anti-inflammatory drugs by the general route and repeated local application of revulsive and anti-inflammatory products.
Infectious diseases in horses
Infectious diseases are no longer as common. The most classic disease is tetanus, which in its usual generalized form results in permanent muscle contractures induced by a toxin secreted by a bacterium. The horse is very irritable, and the slightest noise triggers a tetanic attack. During the evolution, the eyes are partially covered by a white membrane (which corresponds to the nictitating membrane, (it is a third eyelid) and disorders of swallowing are observed which can lead to broncho-pneumonia by false swallowing which darkens the prognosis. Death may occur due to paralysis of the diaphragm or due to complications, particularly respiratory. This disease can be observed in foals and adult horses. For a long time now, it has been possible to protect horses very effectively against this disease and every horse should be properly vaccinated.
Another disease, even if it seems to have disappeared in France in the last few years, should be known rabies. This disease is, as in other species, inevitably fatal. It is characterized by the appearance of symptoms showing the evolution of an encephalitis (inflammation of the brain), associating hyperexcitability and depression, aggressiveness, swallowing disorders, decubitus, pedaling… It is necessary to know that a horse affected by this disease represents an important danger of human contamination because it is often handled by many people before the suspicion is evoked and the diagnosis established.
As for tetanus, a vaccine is available and highly effective, and vaccination is regulated. Other rarer diseases (neosporosis, protozoan myelopathy, intoxications by certain plants such as vetch, poisoning) can be reported, their diagnosis being sometimes difficult.
Finally, viral encephalomyelitis (such as West Nile), some of which are legally known to be contagious, may not only be observed in horses but may also affect humans (these are zoonoses).
Inflammatory and degenerative diseases in horses
Three main examples should be mentioned: grass disease, chronic compression of the cervical spinal cord and laryngeal hemiplegia.
Grass sickness is a condition that primarily affects the organ-vegetative nervous system, also known as the autonomic system. It is also called dysautonomia. It is translated by digestive and cardiac disorders (slowing down of the digestive transit without necessarily expressed pain, decrease of the emission of droppings which become very dry and dark, increase of the cardiac frequency). The cause of this disease is still unknown, and the prognosis is poor, although some forms are curable with long term treatment. However, it has been well demonstrated that horses, and not necessarily all in the same group, contract this disease in the pasture; it is now thought that it is due to a toxin which has not yet been precisely identified. As soon as a case is recognized, it is therefore advisable to remove the horses from the pasture; no other measures are currently documented.
Chronic compression of the cervical spinal cord is caused either by instability of the cervical vertebrae or by bony lesions that compress the cord and/or nerve roots. It is also called “dog’s pain” or “spinal ataxia of the foal” and, depending on the intensity, it is characterized by a lack of balance in the gait, especially observed on the hind legs, the horse giving the impression of waddling, especially when trotting, and most often refusing to back up; when the condition is more advanced, the horse may even fall or have enormous difficulty getting up, generally adopting a seated dog position. This condition is often related to so-called growth or developmental bone diseases, but identical symptoms can be observed in many other nerve disorders affecting the cervical spinal cord, infectious or traumatic. Prevention is based on a balanced diet, particularly in terms of mineral intake. Surgical treatment options exist, including chemical stabilization (by infiltration of the diseased areas) or surgical stabilization, which are major procedures that are not commonly performed.
Laryngeal hemiplegia is a nerve disorder frequently encountered in sport horses. It is due to inflammatory or degenerative damage to the nerve called recurrent which controls the muscles that open the larynx. It is most often an attack on the left recurrent nerve, due to the particularities of its anatomical course. Depending on the extent of the lesion, a simple paresis leading to incomplete opening or a total paralysis leading to an absence of opening of the hemilarynx are observed during the endoscopic examination. Clinically, this neuropathy, which may be associated with other peripheral nerves, is responsible for the appearance of a respiratory noise (especially during inspiration) and the abnormality of the opening of the larynx preventing air from passing correctly leads to an intolerance to effort depending on its importance and the type of use of the horse. This neuropathy may be due to inflammatory conditions of the jugular groove (especially after complications following intravenous injections), but it is observed in horses of generous size and with a large neck. Sometimes associated with a violent inflammation of the throat, in which case a medical treatment can be proposed, it requires a surgical treatment in case of important respiratory discomfort, which consists in keeping the Pheilarynx correctly open to let the air pass through, and in the ablation of the vocal cord to eliminate the noise.
