Equine asthma linked to dorsal displacement of the soft palate

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Dorsal displacement of the soft palate (DDSP) in a horse.
Dorsal displacement of the soft palate (DDSP) in a horse.

More than half of sport and pleasure horses with equine asthma also had dorsal displacement of the soft palate (DDSP), a study in Hungary has revealed.

Upper respiratory tract conditions have received much attention in the causation and treatment of DDSP. Recent research highlights the potential role played by lower airway conditions.

In the normal horse, the soft palate fits snugly around the base of the epiglottis (the front part of the larynx). This allows inhaled air to pass directly from the nasal passages into the trachea. Normally, the horse does not breathe through the mouth.

Dorsal displacement of the soft palate occurs when the soft palate becomes dislodged from its normal position and comes to rest on top of the epiglottis, in the laryngeal opening. When this occurs during high-speed exercise, the high airflow causes the free border of the soft palate to vibrate. This causes significant obstruction to the horse’s breathing and produces a gurgling sound. The horse usually has to slow down and swallow to replace the soft palate in its normal position.

A study by Kinga Joó at the Szent István University, Kaposvár, Hungary and colleagues, reviewed the findings of pleasure and sport horses competing at national level presented for evaluation of suspected equine asthma.

Clinical examination of the horses included endoscopic examination, both at rest and during exercise. Tracheal wash and bronchoalveolar lavage (BAL) were used to collect mucus from the trachea and lower airway.

During the resting examination, a nasal occlusion test was performed to mimic pressure changes that might occur during intense exercise. In many horses this caused the palate to displace.

In all, 22 mild/moderate and 31 severe asthmatic cases were included in the study, a full report of which is published in the Journal of Equine Veterinary Science.

The authors found that 65% of pleasure and sport horses with mild equine asthma showed DDSP during the nasal occlusion test. In horses with severe equine asthma, 79% showed DDSP at rest and all of them had DDSP at exercise.

Horses showing DDSP tended to cough but did not make the typical gurgling sound heard in racehorses. The authors suggest this may be because of the lower rate of airflow in these horses compared with racehorses.

The researchers emphasise the importance of treating the upper and lower respiratory tracts as a single unit, “as lower respiratory tract diseases can often cause upper respiratory functional disorders, whereas upper respiratory obstructions could be a factor in lower respiratory problems”.

They suggest that treatment of dorsal displacement of the soft palate has to be tailored to the cause.

Asthmatic Disease as an Underlying Cause of Dorsal Displacement of the Soft Palate in Horses. Kinga Joó, Ágnes Povázsai, Zsófia Nyerges-Bohák, Ottó Szenci, Orsolya Kutasi. J Equine Vet Sci (2021) 96:103308.
doi:10.1016/j.jevs.2020.103308.

Equine Science Update

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