The integrity of the horse’s entire respiratory system is essential to its performance in sport, so it’s normal to be concerned about a horse that coughs. The respiratory system comprises the respiratory tract (nose, larynx, trachea, bronchial tree) and the lung tissue (pulmonary parenchyma), made up of a multitude of pulmonary alveoli that form a large surface area for gas exchange and, consequently, blood oxygenation (hematosis function). For these gas exchanges to be effective, the respiratory tract must be permeable and the lung parenchyma must be intact to prevent horses from coughing.
Anatomically and functionally, horses have a number of peculiarities that help us to better understand certain ailments. Naturally, the horse cannot breathe through its mouth, due to the particular length of its soft palate. In the first respiratory tract, there are certain semi-elastic structures that are mobilized during respiratory movements and can impede the passage of air. Finally, in the pulmonary region, the terminal ducts of the bronchial branching, the bronchioles, are longer than in other species and have their own highly-developed musculature. Moreover, in the normal state, there are a number of communications between the vessels of the small and large circulation in the lung.
As a result, disorders of the primary respiratory tract are often functional in nature, and particularly obstructive (impeding the passage of air), while pulmonary disorders often involve damage to the bronchioles and alveoli.
Horse cough: disorders of the primary respiratory tract in horses
Depending on the case, they can be characterized by an abnormal discharge of secretions from the nasal passages (known as jetage), coughing (which in these cases is a strong, greasy cough), or a respiratory noise (known as cornage), which can be inspiratory and/or expiratory, and can be accompanied by a drop in performance and intolerance to exertion. Coughing may be unilateral or bilateral, and may sometimes contain blood (known as epistaxis) or be present when the horse lowers its head (in which case it often comes from specific cavities such as the sinuses or guttural pouches).
Horse cough: sinusitis in horses
Most often caused by infection, more rarely by congenital malformation, non-specific inflammation or tumour. Sinus infections can be primary (as a complication of strangles, for example) or secondary to dental infection; indeed, there is a close anatomical relationship between the maxillary sinus and the molar arch. Recognition of sinusitis is based on careful examination of the oral cavity, radiographic examination of the sinuses or, in the case of trepanning, endoscopic examination. Treatment involves local drainage to irrigate and clean cavities with antiseptic solutions. Systemic treatment may involve antibiotics and secretion modifiers to promote elimination.
Horse cough: guttural pouch disorders in horses
These structures are highly specific to equids. They are a diverticulum of the auditory tube that forms two pouches communicating with the pharynx. Each has a volume of around 300 milliliters and is filled with air. Their precise role is not yet known. What we do know is their anatomy and pathology. Two conditions deserve special mention: empyema and mycotic diseases. Empyema is a purulent collection of varying size inside one or both guttural pouches. It is generally due to the pathogenic action of streptococci (which are the germs most often isolated), but others may also be involved. It is one of the classic complications of strangles, often involving the abscessation of lymph nodes in close contact with these structures, which pour pus into the guttural pouches. It has also been shown that the guttural pouches are the place where the germs responsible for strangles can be harboured, even in non-diseased horses, and that they are therefore the site of healthy carriage, which explains the recurrence of this infection within a group. Recognition of empyema is based on radiographic or, better still, endoscopic examination of the guttural pouches: it is then possible to take samples for bacteriological analysis and to insert drains. In some cases, it may be preferable to perform a transcutaneous drainage operation.
Mycotic disorders of the guttural pouches are not uncommon, and can be very serious in terms of the amount of bleeding they cause. For reasons that are as yet imperfectly understood, fungi can develop in the guttural pouches, generally along the vascular-nervous tracts. Depending on the extent and location of this development, the repercussions can vary: nerve disorders, in particular swallowing problems, or more or less extensive bleeding, cataclysmic if the internal carotid artery is ruptured. Any bleeding, however minor, should prompt an endoscopic examination of the guttural pouches to detect any mycosis. If detected early, surgical treatment is recommended to eliminate the irrigation needed for the fungus to develop.
Horse cough: laryngeal paralysis in horses
In the vast majority of cases, this is a left hemiparesis or hemiparalysis (see the section on nerve disorders). It is responsible for an obstruction to the passage of air, resulting in the appearance of an essentially inspiratory noise (comedor horse). Depending on the level of sporting use, this obstruction can lead to a reduction in performance, and surgical treatment with a laryngoplasty can be envisaged, bringing an improvement in around three-quarters of cases.
Horse cough: follicular pharyngitis in horses
There are a multitude of lymphoid formations scattered throughout the throat of horses, which do not have tonsils as such. Depending on the degree of throat irritation, caused either by pathogens (such as certain viruses) or mechanical irritation (e.g. dust), these formations can become enlarged and cause discomfort (pain on swallowing, coughing, gnawing). This condition is easily recognized by endoscopic examination, but it should be noted that lymphoid hyperplasia is very often observed in young horses without them being bothered (in this case, it’s more a demonstration of permanent irritation, notably by a polluted environment, and there’s no need to suggest treatment).
When pharyngitis is severe, local or general anti-inflammatory treatment may be suggested.
Horse cough: non-infectious inflammatory lung diseases in horses
Inflammatory lung diseases are generally characterized by coughing (which may be more or less severe, dry or, on the contrary, oily), abnormal breathlessness (at rest or, more often, after exertion), intolerance to exertion and, quite often, the presence of jetage, which is generally not very significant but constant, particularly during and after exertion. In most cases, abnormal respiratory movements are observed: in particular, nasal mobilization at rest and expiration in two stages, the second of which corresponds to a push by the abdominal muscles to expel air from the alveoli more efficiently (what the ancients called the push line).
In recent years, the development of numerous investigative techniques has enabled us to better understand the genesis of these conditions. In the vast majority of cases, it’s a matter of permanent irritation of the small airways by substances contained in dust (airborne contaminants), which reach the bronchioles and alveoli: they trigger inflammation of these small airways, with production and/or modification of secretions, reduction in lumen size, abnormal contraction of the peribronchiolar muscles; air is able to enter the alveoli on inspiration, but the reduced calibre of the airways, which is greater on expiration, requires abdominal participation on expiration (hence the appearance of this two-stage expiration); irritation naturally triggers episodes of coughing, which is not very strong and is most often dry. These conditions are often observed in horses living in closed stalls, to a lesser degree when there is an opening to the outside, and even less or hardly at all in meadow horses.
Sometimes, however, this inflammation of the small airways is actually allergic to a particular substance: this is the case with certain moulds sometimes found in poorly preserved hay. The same disorders can be observed, but sometimes at the onset or during the course of the disease, attacks of acute respiratory difficulties can lead one to think of real asthma attacks (formerly known as bouts of wheezing), requiring emergency treatment.
Recognition of these conditions is clinically based, but can also be supported by additional investigations (chest X-rays, endoscopy and taking of samples, intradermal reactions, respiratory function tests).
Therapeutic management of these conditions requires the prescription of hygienic measures, starting with environmental hygiene. It may be necessary to administer anti-inflammatory drugs and bronchodilators when there is a major obstructive disorder. These drugs can be administered by aerosol or nebulization, which are now well developed. But any treatment will only be successful if the environment is correct, especially if a substance is found to be responsible, and its elimination must be complete and systematic.
It is extremely rare for these conditions to result in destruction of the pulmonary alveolar walls, which is why the term “pulmonary emphysema” should be banished from the horseman’s vocabulary.
Exercise-induced pulmonary haemorrhage is a well-recognized entity in racehorses, but also in eventers and show jumpers. Often associated with inflammation of the small airways, they are observed after often intense exercise, but are not necessarily externalized; systematic endoscopic examination of racehorses after exercise shows that bleeding has occurred without hemorrhagic jetage being observed. The mechanisms of this bleeding are not well understood, and few therapeutic or prophylactic proposals have reached a consensus.
Horse cough: bronchopulmonary infections in horses
Accompanied by a febrile syndrome, at least initially, they cause significant changes in respiratory movements. Symptoms vary in severity according to their origin. In the case of infection following false swallowing, the symptoms can be very serious, even leading to the horse’s death. In the case of bacterial complications of viral diseases, or rare complications of initial strictly inflammatory diseases, the symptomatology is variable. In all cases, they must be recognized as early as possible, so that a sustained course of antibiotics can be offered, combined with anti-inflammatory treatment and hygienic measures to ensure a dust-free, well-ventilated environment.
Particular mention should be made of pleuropneumonia, a fortunately rare condition, but classically observed after long-distance transport or stress induced by a sporting event or anaesthesia, for example. This is a pulmonary and pleural infection characterized by the presence of inflammatory fluid in the pleural cavities. This explains the severe respiratory difficulties observed, and the need to puncture and drain these cavities. Other complications, such as endotoxemia, may further complicate the picture. Recognition of this condition must be early, and involves not only clinical but also radiographic, ultrasound and endoscopic examination.
The considerable progress made in the medicalization of equids in general, and horses in particular, has not escaped the horseman’s notice. While the observational skills of our elders – who are always worth reading and re-reading, as their descriptions lead contemporary clinicians towards a better semiological approach – have enabled the dismemberment of many equine diseases, today we are struck by the technicality at the service of the horse doctor: radiographic, echographic, scintigraphic and even tomodensitometric examinations, biological tests of all kinds, endoscopic examinations, all provide the comfort needed to establish precise diagnoses and institute specific, cutting-edge treatments. Thirty years ago, did we think that abdominal surgery would ever be possible, or that joint surgery would ever be envisaged? Did we imagine that we would be able to vaccinate our horses and carry out proper pest control? Could we cherish the hope of better gynecological care? Today, this is possible, and the progress of this medicine is not yet over, judging by the large number of horse-specific research programs (in osteoarticular, respiratory, parasitic, reproductive, neonatal and sports medicine pathologies, etc.).
This ever-increasing medicalization is perfectly justified, firstly to ensure the well-being of our horses, whether they are athletes or companions for man; secondly, because in certain fields (e.g. infectiology, with the emergence or re-emergence of certain infectious diseases such as West Nile) the horse has a legitimate place in comparative bio-pathology; and thirdly, because it is one of man’s duties to ensure, in return for all the pleasures provided by this noble animal, the protection of domestic animal species.
