Conditions of the respiratory tract



Conditions of the respiratory tract



Congenital/developmental disorders


Wry nose (Fig. 3.1)


Wry nose, or deviated rostral maxilla and associated nasal septal deviation, is a congenital deformity in the horse. The deviation can be very mild to severe. A foal with wry nose will have the upper jaw and nose deviated or turned to one side. A deviated nasal septum is also usually present, which results in obstruction of the airway and difficulty breathing. This is the greatest functional concern with wry nose. There will usually be malocclusion (poor alignment) of the teeth, although most foals can still nurse and in most cases are bright and active.



The etiology of maxilla deviations is often unknown. Failure of proper embryologic development of the hard palate and maxilla may be associated with possible genetic defects. Abnormal in utero positioning has also been proposed.


Wry-nosed foals can also have other deformities of the neck and occasionally of the limbs. It is very important to further evaluate the foal for other types of genetic defects.




Epiglottic and pharyngeal cysts (Figs. 3.23.6)


Epiglottic and pharyngeal cysts are fluid-filled structures that do not communicate with an epithelial surface. These cysts can be found in the subepiglottic tissues, in the dorsal nasopharynx and within the soft palate. In foals these cysts are considered congenital and depending on their location may represent embryonic remnants of the thyroglossal (sub-epiglottic) and craniopharyngeal (pharyngeal) ducts. Thoroughbred and Standardbred foals are most commonly affected. The presence of the cyst at this site may have little effect upon the well-being of the animal and may be detected incidentally at any age during endoscopic examination of the pharynx. The cysts may be relatively small in the early years of life but commonly enlarge slowly with time and therefore a progressively deteriorating respiratory noise with exercise limitations develops. Horses in which the epiglottis is very prominent and apparently upright, giving the impression of being tightly held by the rostral border of the soft palate, may be so because of an epiglottic cyst under the soft palate. In most such cases, however, no cyst can be identified and radiographic examination will usually confirm or deny their existence. Where no cyst is present the position of the larynx relative to the soft palate is regarded as a normal variant.







Foals with large cysts may present in respiratory distress or be seen to collapse while nursing. Coughing, nasal discharge, nasal milk reflux and aspiration pneumonia are common clinical signs.




Diagnosis and treatment



• Sub-epiglottic cysts. Endoscopy is essential for diagnosis. Make sure that swallowing is observed during endoscopy to allow observation of the ventral aspect of the epiglottis and the caudal aspect of the soft palate. Cysts located in the sub-epiglottic tissue may not always be visible while the epiglottis is in its natural position relative to the soft palate, being located under the rostral palatine border. Oroscopic examination may be required for diagnosis.


• Pharyngeal cysts. These are not directly visible endoscopically, but symmetric or asymmetric dorsal pharyngeal compression, which is not attributable to guttural pouch enlargement, is visible and lateral radiographs of the pharynx confirm their presence.


• Concurrent developmental defects of the epiglottis are sometimes present and these influence the clinical effects and endoscopic and radiographic appearance.


• Repeated dorsal displacement of the soft palate may be present, possibly as a result of inadequate free rostral length or inadequate stiffness of the epiglottis.


• Surgical intervention will be warranted. Surgical resection via a ventral midline laryngotomy works best but with smaller cysts laser ablation may suffice.



Guttural pouch tympany (Figs. 3.73.10)


Guttural pouch tympany is a common, possibly developmental, disorder involving usually one (but occasionally both) of the openings (ostia) and/or the pharyngeal component of the auditory tube in the nasopharynx. It is more common in fillies than in colts and Arabians appear to have a breed predilection. The etiology is not exactly known but it appears that the salpingopharyngeal fold (redundant tissue) is excessive, causing the external ostia to act as a one-way valve. This one-way valve action will cause the accumulation of air in the guttural pouch. The affected pouch is distended with air to form a non-painful, elastic swelling in the parotid region. The swelling is most prominent on the affected side, but can extend across the neck and give the impression of bilateral involvement.






Within the first few weeks of life (but occasionally up to 1 year of age) affected foals develop a prominent, non-painful, non-elastic, tympanitic distension in the parotid region.


Stertorous breathing and possibly dysphagia with nasal regurgitation of food, as a result of dorsal pharyngeal compression or distortion may be evident, particularly if the neck is flexed. Suckling foals may have considerable difficulty feeding from the mare and sometimes adopt bizarre feeding positions in an attempt to limit the pharyngeal distortion and allow normal swallowing.






Tracheal collapse (Figs. 3.11 & 3.12)


Tracheal collapse might be related to abnormal tracheal cartilage matrix and is most often diagnosed in ponies and miniature horses. Limited lengths of the trachea are affected but longer lengths are sometimes involved. The trachea is flattened ventro-dorsally or, more rarely, laterally. The passage of a food bolus through the esophagus can be appreciated during tracheal endoscopy due to the flaccid dorsal ligament which replaces part of the normally solid cartilaginous ring. Some cases are found to have intact tracheal rings with a marked flattening and sharp angles at each side. Typically signs are not noted until the animal is older and is often not noted until adulthood. Severely affected animals will develop a ‘honking’ inspiratory and expiratory sound. Tracheal stenosis and collapse can also develop dramatic clinical signs, including respiratory stridor, dyspnea and cyanosis. More severe signs are usually associated with concurrent respiratory disease or sudden increased exertional demands.




Spiral deformity of the trachea is a developmental abnormality, also primarily affecting the miniature breeds, in which the tracheal rings take on a spiral contour. This is usually more prominent in the proximal cervical trachea. Animals with spiral deformity of the trachea seldom have any clinical effects, with the defect normally being found incidentally during respiratory tract endoscopy or post-mortem examination.





Epidermal inclusion cysts (atheroma) (Fig. 3.13)


These are characteristically located in the caudo-dorsal area of the nasal diverticulum (false nostril). These spherical structures are usually unilateral and 2–5 cm in diameter, but in unusual circumstances may be bilateral and much larger. They are only of cosmetic significance. They are occasionally apparent in weanlings but are usually presented in young adults. The cysts are soft, fluctuant and non-painful but may also have a firm texture giving the impression, on palpation, of a solid mass. They may be moveable in the surrounding tissue or relatively fixed, and contain a sterile, gray, creamy, odorless, thick material.





Choanal atresia (Fig. 3.14)


This a rare disorder that is due to a failure of the breakdown of the buconasal membrane. This membrane normally separates the embryological buccal and nasal cavities and breaks down during later stages of development. There is therefore no communication between the oropharynx and the nasopharynx.



Bilateral atresia results in immediate respiratory distress, cyanosis and decreased/absent airflow from the nares following birth. Unilateral atresia results in a lack of airflow through the affected nasal passage.




Branchial cysts (Fig. 3.15)


Branchial cysts are uncommon embryonic anomalies of horses. The cysts result from malformation of one of the five branchial arches during embryogenesis. These cysts typically appear as smooth, round, mobile masses and often do not cause any clinical abnormalities, although large cysts may cause discomfort and can disrupt pharyngeal or laryngeal function. Many are not apparent until weaning age with late recognition possibly as a result of delayed secretion of fluid by the epithelial lining.





Maxillary sinus cysts (Figs. 3.163.19)


Congenital disorders of the nasal cavities and paranasal sinuses are very rare. However, unilocular or, more usually multilocular, fluid-filled maxillary cysts may be encountered within the paranasal sinuses in young foals. The caudal compartment of the maxillary sinus is most often affected but the cysts may extend from here into the frontal sinus. They are possibly related to the germ buds of the permanent cheek teeth, although most affected foals show no developmental dental defects in later life. Congenital cysts are obvious at birth or develop in the first few weeks of life. Very large cysts have a significant effect upon the nasal cavity and facial appearance. Progressive enlargement results in a worsening obstruction of the nasal cavity and displacement of the nasal septum. Distortion of the maxilla and the nasal cavity, with bony resorption and dental defects, may result.






The clinical effects are largely dependent upon the extent of dental and nasal distortion. Where the erupting premolar teeth are grossly displaced by progressive bone resorption, foals may show difficulty with mastication with food material accumulating in the sides of the mouth. There may also be some loss of solid food from the mouth (quidding) but there is usually no difficulty with suckling, except where the hard palate is also distorted. They often have a marked effect on respiratory function when the distortion of the nasal cavity is sufficient to result in occlusion of both nasal cavities. While most of these cysts have a thick spongy epithelial lining others have a thinner mucosal lining. In both types, incomplete plates of bone are often present. The cyst itself is usually filled with a sterile, turbid, yellowish fluid with little or no odor. In some cases the fluid may be mucohemorrhagic.




Maxillary mucocele


The congenital absence of an effective naso-maxillary opening creates a discrete single-structured secretory cyst within the affected maxillary sinus, and lined by the normal sinus mucous membrane, known as a mucocele. In these cases, the contents of the cyst are thick and mucoid but, in contrast to the sinus cysts and infected sinuses, are usually clear and sterile.




Epiglottic hypoplasia (Fig. 3.20)


The Thoroughbred has been shown to be prone to what is believed to be a developmental epiglottic hypoplasia which may be diagnosed where the epiglottis appears, endoscopically, to be visibly short, or when it appears to be flaccid regardless of the length (which may be normal or, in some cases, greater than normal). Lateral radiographs of the pharynx will also identify the shortened epiglottic cartilage which can usually be measured accurately, making allowances for magnification. The normal epiglottic length is 8–9 cm and an abnormal shortening is usually associated with a length of less than 7 cm (some authors say 5.5 cm). These animals appear to be particularly liable to epiglottic entrapment and dorsal displacement of the soft palate (laryngopalatal dislocation). There are few significant primary effects from epiglottic hypoplasia itself, with most of the secondary consequences affecting performance through airway distortions and displacements.





Fourth branchial arch defects


This is a rare syndrome of congenital defects resulting from a failure of development of some or all of the derivatives of the fourth branchial arch. Two typical features of fourth branchial arch defects are rostral displacement of the palatopharyngeal arch, which in some cases may only be detected during dynamic studies and defective arytenoid motility.


The condition is important with respect to abnormal respiratory noises and poor exercise tolerance. Most cases are only detected when extra exercise-demands are placed upon them, and they cannot open the aditus laryngis to allow an increased air supply. Affected horses show a severe limitation to exercise with harsh rasping inspiratory (and often expiratory) sounds which are localized around the larynx. Other clinical signs include eructation, nasal discharge, coughing and recurrent colic.




Non-infectious disorders


Foreign bodies (Figs. 3.21 & 3.22)


Foreign bodies may be detected at any site from the nares to the trachea and are often associated with the type of diet the horse is being fed. Thorny twigs, brush bristles and other sharp objects lodging in the pharynx are possibly more common than foreign bodies within the nasal cavity. The presenting clinical signs depend on the site and size of the foreign body.






Clinical signs



• Nasal cavity. Those lodged in the nasal cavity result in a unilateral nasal discharge of acute onset, often with small amounts of fresh blood. Affected horses show considerable discomfort, being head-shy and snorting a great deal. Sneezing is unusual in the horse under any circumstances. Untreated cases may result in local abscesses or the development of mineralized concretions within the nasal cavity and a foul-smelling breath from the affected nostril.


• Pharynx. Acute-onset dysphagia with complete or partial respiratory obstruction. Large solid objects such as pieces of apple would be expected to have marked effects upon respiration, particularly on inspiration and the effects are consequently dramatic and of peracute onset. In most cases these are transient with the object dislodging spontaneously and resolution is immediate and complete. In some cases, however, the object appears to be firmly lodged and a life-threatening respiratory obstruction may be presented. Horses which habitually chew wooden fences and doors are also liable to pharyngeal obstructions as a result of pieces of wood breaking off. Sharp, small foreign bodies present little immediate threat to life and do not often cause respiratory embarrassment. However, an acute onset of severe and distressing difficulties with swallowing is frequently presented. The affected horse presents with nasal regurgitation of food material and saliva and attempts to drink are accompanied by nasal regurgitation and expressions of pain such as squealing and arching of the neck. Occasionally unilateral (or in some cases bilateral) epistaxis is present.


• Trachea. The inhalation of small grass seeds and particles of dust and grass is common when horses are exercised hard under appropriate conditions. These seldom cause any marked effect and coughing is usually sufficient to dislodge the foreign matter. A residual tracheitis may be present for a day or two thereafter. Plant twigs represent a relatively common tracheal foreign body and are often responsible for an acute onset of a severe and frequently paroxysmal coughing. Tracheal hemorrhage is usual and there is often some inflammation and reflex spasm of the airway.




Facial trauma (Fig. 3.23)


Traumatic lesions involving the facial bones result in variable distortions of the shape of the head, often as a consequence of depression fractures of the facial, frontal, nasal and maxillary bones. Facial trauma may also impair the drainage from the maxillary and/or frontal sinuses. Relatively minor trauma to the facial bones commonly results in damage to, or disruption of, the bony portion of the nasolacrimal duct.







Arytenoid chondritis (Figs. 3.243.26)


Arytenoid chondritis is abnormal enlargement of the arytenoid cartilages resulting from chronic inflammation. It is seen most commonly in horses working at high speeds and as such Thoroughbreds and Standardbreds are primarily affected. Trauma, inflammation and infection have all been cited as possible causes. Histopathological findings in most cases are consistent with a chronic inflammatory process. The affected cartilage is thickened and laminated with fibrous connective tissue. The condition is typically unilateral but secondary contact damage (‘kissing lesions’) between cartilages is common.





A significant loss of effective abduction arises and results in the appearance of a flaccid aditus laryngis with collapse of one or both arytenoids into the airway. On some occasions the aditus laryngis may be reduced to a mere slit with neither abduction nor adduction present.





Diagnosis and treatment



• Endoscopy is normally sufficient for a diagnosis although some cases may mimic laryngeal hemiplegia. Additional findings which are variably present include ulceration, granuloma formation, necrosis and cavitation of the arytenoid cartilage, sinus tracts, deformity of the corniculate process or kissing lesion on the contralateral cartilage.


• Medical therapy is normally attempted primarily depending on the level of deformity present. This includes rest, antibiotics and anti-inflammatories. Throat sprays and nebulization are also useful and hyperbaric oxygen therapy has been used in some cases with anecdotal reports of success.


• In cases in which medical therapy does not give satisfactory results surgical options can be considered. Transendoscopic laser debulking is recommended for horses with granuloma formation. Partial, complete or subtotal arytenoidectomy may be performed depending on the individual case.



Tracheal perforation (Figs. 3.273.29)


Blunt trauma to the ventral neck may cause tracheal fracture or avulsion of the tracheo-laryngeal junction. Tracheal perforation with resultant subcutaneous emphysema, secondary to blunt trauma, can also occur. Tracheostomy can also result in secondary subcutaneous emphysema but is usually less extensive than that seen with tracheal perforation. Cases in which the trachea is bilaterally (ventral and dorsal is the most common bilateral lesion) perforated are more likely to develop severe complications.









Tracheal chondroma (Figs. 3.30 & 3.31)


The insertion of emergency, or permanent, tracheostomy tubes or traumatic injuries to the trachea are common causes for the development of localized granulation tissue within the trachea. This occurs more particularly when the cartilage rings of the trachea are damaged during the procedure with the resulting tissue being classified as a chondroma, but which may only consist of granulation tissue. The healing of tracheostomy wound sites is often accompanied by distortions of the tracheal rings beneath the mucosa, but it is unlikely that these would be responsible for significant impairment of air flow except where consequent tracheal stenosis or collapse develops, following cartilage damage and/or necrosis.






Pneumothorax (Figs. 3.323.34)


Pneumothorax is classified as either open or closed. In either case the influx of air into the pleural space causes equilibration of pleural pressure with atmospheric pressure and subsequent lung collapse. An open pneumothorax results from an injury to the thoracic wall leading to an influx of free air into the pleural space. A closed pneumothorax is the leakage of air into the pleural space from a pulmonary source such as a bronchopleural fistula. A tension pneumothorax occurs when a section of traumatized lung acts like a ‘valve’ that allows the air to enter but not leave the pleural space. Thoracic drains are a frequent entry point for air into the pleural cavity and horses with thoracic drains in place should be under constant monitoring. Affected horses usually present with exaggerated abdominal lift, elevated respiratory rate and flared nostrils. Bilateral pneumothorax will result in cyanosis and severe dyspnea.





Multiple, smaller bullae in the lungs are a rare complication of longstanding allergic (or other) respiratory diseases which result in loss of pulmonary compliance (elasticity).




Diagnosis and treatment



• Percussion of the chest will establish an abnormal resonance and auscultation will reveal an absence of audible lung sounds over the affected areas.


• Thoracic ultrasonography will reveal horizontal air artifacts in the midthoracic or dorsal regions, thereby not allowing the examiner to identify the sliding motion of the visceral pleural against the parietal pleura. Thoracic radiography reveals a horizontal shadow beneath the thoracic transverse processes, which is consistent with a ‘line’ representing the collapsed lung(s). If radiology and/or ultrasonography are not available, then the clinician can use response to suction via a thoracocentesis as a diagnosis.


• The treatment of choice is prompt removal of free air via a thoracocentesis and suction. This procedure rapidly re-expands the lung and relieves the respiratory distress. If an open pneumothorax is diagnosed then surgical closure is indicated.



Exercise-induced pulmonary hemorrhage (EIPH) (Figs. 3.353.44)


Horses of all breeds can suffer from pulmonary bleeding during heavy exercise.












Rupture of the alveolar capillaries occurs secondary to exercise-induced increase in transmural pressure. Possible contributors to the pathogenesis include: small airway disease, upper airway obstruction, hemostatic abnormalities, changes in blood viscosity and erythrocyte shape, intrathoracic shear forces associated with gait and bronchial artery angiogenesis. The relationship between exercise-induced pulmonary hemorrhage and chronic airway disorders is reasonably well established, but it is also clear that not all horses affected by one condition will inevitably suffer from the other. Predisposing factors include breed (more common in Thoroughbreds) and age (more common in older horses).





Diagnosis



• Tracheobronchoscopy can be used to estimate the severity of EIPH through a grading system (see Table 3.1). However, the relationship between the amount of blood in the large airways and the actual amount of hemorrhage has not been definitively established. This examination is best carried out 30–90 minutes after exercise. If the first examination is negative but there is a high suspicion then the examination can be repeated 1 hour later.



• Tracheal aspiration and bronchoalveolar lavage: the presence of red blood cells or hemosiderophages in tracheal fluid or BALF provides evidence of EIPH. Red blood cells are present for at least 1 week after strenuous exercise and up to 21 days in the case of hemosiderophages. These procedures are also useful for the detection of concurrent respiratory tract infections.


• Thoracic radiography may demonstrate the presence of densities in the caudodorsal lung fields but is not indicative of the severity of EIPH. It is most useful for determining the presence or absence of other disease processes that may contribute to the pathophysiology, such as pulmonary abscesses.


• Ultrasonography can also be used with ‘comet tail’ lesions detected in the caudo-dorsal lung fields associated with areas of hemorrhage.





Recurrent airway obstruction and inflammatory airway disease (Figs. 3.453.49)


Horses and ponies are commonly affected by non-infectious airway diseases such as recurrent airway obstruction (RAO) or inflammatory airway disease (IAD). RAO (also known as heaves) is one of the most common respiratory disorders of the horse in temperate areas of the world, and occurs particularly where horses are stabled for long periods and fed and bedded on preserved cereal and/or grass products. The probable etiology of the disorder is repeated mucosal allergic challenge in the conducting airways. A similar condition is found in some pastured horses and is termed summer pasture-associated obstructive disease. Both conditions are characterized by reversible airway obstruction, with neutrophil accumulation, mucus production and bronchospasm.







IAD is a less well-defined syndrome with different presentations in different groups of horses. The pleasure horse with IAD may have obvious nasal discharge, cough and overheating, whereas the young racehorse may show poor recovery from peak exercise or poor performance. The etiology is believed to be largely the same as RAO with environmental allergens playing a significant role; however, some horses, particularly young racehorses in training, may also have an infectious component to the etiology.




Clinical signs



• The exercise tolerance of affected horses is frequently adversely affected, with a significant number being presented, initially, for investigation of poor or inadequate athletic performance.


• Cases generally have an abnormally high resting respiratory rate with a variable degree of nostril flare.


• A chronic, harsh, non-productive cough is characteristic.


• Without treatment, the severity of the cough often increases over weeks or months, sometimes with episodes of a more acute syndrome superimposed from time to time.


• Severely affected horses lose weight dramatically and the increased expiratory effort commonly results in marked hypertrophy of the muscles of the caudo-ventral thorax producing the so-called ‘heave line’. In the severe cases, an obvious, extra, expiratory ‘push’ from the abdominal and thoracic muscles is present, possibly with an associated grunt.


• A slight or sometimes more profuse, bilateral, postural, catarrhal nasal discharge is usually present.



Diagnosis



• Clinical signs and history of a seasonal disorder that can be altered by husbandry practices.


• Endoscopic examination of the respiratory tract shows poor mucus clearance from the trachea.


• Broncho-alveolar lavage (BAL) reveals inflammatory cells in proportion to the severity of the underlying disease and this provides an effective quantitative measure of the severity of the underlying pathology. BAL is preferable to transtracheal washing for diagnosing and differentiating RAO from infectious respiratory disease.


• Radiographic examination of the thorax may demonstrate an increase in bronchial and interstitial patterns but this can be difficult to interpret in light of normal changes in bronchial pattern associated with advancing age. Radiography is best used in these cases to differentiate from other, more focal disorders.


• Serum allergen testing and intradermal allergy testing have not proven very useful in identifying specific allergens in the horse’s environment.




Laryngeal hemiplegia (Figs. 3.503.56)


The recurrent laryngeal nerve innervates all of the intrinsic muscles of the larynx with the exception of the cricothyroideus. Neuropathy of this nerve results in laryngeal hemiplegia which is defined as a failure of abduction of a structurally normal arytenoid cartilage because of decreased or absent motor fuction in the cricoarytenoideus dorsalis muscle. In most cases no cause for the neuropathy can be found and thus is termed idiopathic. Most frequently, but not exclusively, the left nerve is involved. The paralysis is usually only left-sided, and may be partial (in which there is some abduction movement of the arytenoid) or complete (in which no abduction is visible).









Young horses, between 2 and 6 years of age, and horses over 16 hands in height, are, however, most often affected. Certain breeds, including the Hannovarian, Shire, Irish Draught, Dutch Warmblood and other large breeds, appear to be particularly liable to severe forms of the condition which apparently develop spontaneously. The Thoroughbred, Standardbred and Quarter Horse breeds are also affected commonly with a range of mild to severe forms of the disorder with up to 80% of Thoroughbred horses possibly affected to some extent. The majority of these have mild degrees of the condition in which little or no clinical effect is detectable. Most horses with significant laryngeal neuropathy are presented for investigation of inspiratory noises ‘roaring’ and/or poor exercise tolerance.




Diagnosis



• The condition may be suspected on the basis of an inspiratory noise but endoscopy is required to confirm the diagnosis. (Table 3.2 outlines a grading system for laryngeal anatomy and function.)



• The ‘slap test’, which tests the integrity of the thoraco-vagal reflex by observing (or palpating) contralateral laryngeal adduction and abduction in response to a ‘slap’ applied to the thoracic wall, may also be used to demonstrate the malfunctioning of the affected side. The atrophy of the muscle may be suggested by palpation of the muscular process of the arytenoid on the affected side which becomes characteristically prominent. However, a horse may have normal laryngeal function at rest but still have signs of dysfunction when exercised and atrophy of the cricoarytenoideus dorsalis may not be apparent in horses in which the disorder is of recent onset.


• Comparative endoscopic examination of the larynx, at rest and at exercise, is particularly useful in establishing the extent of the dysfunction and to determine whether any prior attempts have been made at surgical relief of the obstruction. Due to possible normal function at rest and abnormal function during exercise traditional methods of detection have consisted of listening for inspiratory noises during exercise in addition to scoping at rest but this may in many instances now be replaced by dynamic endoscopy during exercise in horses which are normal at rest. Right-side and bilateral paralyses are sometimes encountered but the etiology of these are usually better defined.



Treatment



• Surgical correction is required if significant airflow obstruction is present. Laryngoplasty, a prosthetic ligature, is currently widely used to stabilize and abduct the affected arytenoid cartilage. Complications following this procedure include: failure to maintain abduction of the arytenoids cartilage, dysphagia and rarely aspiration pneumonia, chronic infection of the prosthesis, ossification of the cartilage, intraluminal polyps, laryngeal edema and chondritis. Horses which have been subjected to this procedure show a stabilized (immobile) arytenoid on endoscopy.


• Lateral ventriculectomy (Hobday’s operation), in which the lateral laryngeal ventricles are surgically ablated, has been used for many years to reduce the respiratory noise. It does not however alleviate the increased impedence to airflow during exercise if used alone. Endoscopic examination will readily detect the absence of one or both laryngeal ventricles.


• Some cases which prove refractory to treatment by the milder surgical interferences are subjected to sub-total arytenoidectomy and the endoscopic appearance of these is very obvious.

Feb 27, 2017 | Posted by in EQUINE MEDICINE | Comments Off on Conditions of the respiratory tract
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