What is DDSP? Well the letters stand for Dorsally Displaced Soft Palate. Why is understanding this disease important to Standardbred and Thoroughbred racing (or any performance horse)? While it is generally not a career ending disease, it certainly can be very frustrating to diagnose and manage in the racehorse and result in very poor performance and loss of earnings. Diagnosis of DDSP is based on a history of poor performance near the end of the mile, a respiratory noise (usually expiratory gurgling), occasional coughing while eating hay or grain, and endoscopic exam of the upper airway during or after exercise. This disease can be a problem in any age of racehorse, but it is probably diagnosed most frequently in 2-3year olds. Endoscopic exam on a treadmill or with a dynamic endoscope may be necessary. Sometimes bruising is noticed with the endoscope exam after training or racing from the dramatic vibrations occurring in the throat or pharynx. Soft palates can displace more easily during or following an upper respiratory infection. So while displacement when sick may not be that unusual, this could indicate a tendency for that particular horse to be more prone to displace even when not sick. Since all the muscles and nerves in the pharynx or throat are interrelated in form and function, conditions like pharyngitis, guttural pouch infections, laryngitis, lymphoid hyperplasia, dynamic collapse of the pharynx, sub epiglottic cysts, congenitally small epiglottis, and tracheitis, could all contribute to the events leading up to DDSP during a training mile or race. Not to mention driving and racing events that shut off the horse’s air. Anything that alters the normal air flow and air pressures in the back of the throat and doesn’t allow for an airtight seal between the soft palate and the epiglottis will cause DDSP. The epiglottis is the other structure contributing to the DDPS. The epiglottis is the valve that opens and closes over the voice box or larynx. It is located deeper in the horse’s throat then the soft palate. With each swallow or deglutition, the epiglottis closes over the larynx to prevent food from being forced into the trachea. At the same time the soft palate rises up or is pushed up by the tongue as it pushes food into the opening of the esophagus headed toward the stomach. This elevation of the soft palate prevents food from being forced into the back of the nasal passage. After the deglutition is complete the tongue relaxes, the soft palate drops back down and the epiglottis moves away from the larynx to rest in its normal position on top of the soft palate, opening the airway and allowing the horse to exhale. Try this yourself. Swallow and relax. You will feel your tongue press in the back of your throat as you swallow and then, when completed, as your tongue relaxes with your mouth closed you exhale through your nose. If a tight seal is not completed between the back of the soft palate and the front of the epiglottis, or if the epiglottis is too small and it cannot rest on top of the soft palate, the epiglottis and soft palate trade places, i.e., the epiglottis comes to rest under the soft palate and we have a dorsally displace soft palate (dorsal refers to being above). Horses are considered obligate nasal breathers. That means they have to breathe through their noses. They do not breathe through their mouths…normally. If you see or hear a horse breathing through his mouth, his soft palate has to be displaced. Our soft palate and epiglottis are not arranged in the same fashion as the horse so we can choose if we want to breathe though our mouth or nose…horses cannot choose. If they come off the track open-mouth breathing, their palate is displaced. With the soft palate above the epiglottis the exhaled air causes violent vibrations of the free margin of the soft palate. That results in air turbulence, bruising and functional asphyxia. The horse cannot get enough air to compete and begins to slow down. I believe horses can feel this event about to happen and may slow down before the displacement actually takes place. But by that time, a racing length may have been lost, not to mention the purse check. If the horse learns to swallow when this event occurs, the palate and epiglottis will return to their normal orientation and the horse may be able to catch his breath and complete the mile competitively. Additionally, the dramatic air pressure changes that occur with DDSP can greatly alter the tracheal and pulmonary air pressures. These air pressure changes can result in more cases of, and more severe, bleeding episodes. Treatment of DDSP with all the tools in the toolbox may be one of the best ways to minimize bleeding episodes (EIPH). Treating DDSP will not stop bleeders, but might help. Treatment should be targeted at an accurate diagnosis and treatment of the root cause, especially if the horse is sick. But general considerations can include equipment changes like a tight cavesson, a figure 8 cavesson, a can under the throat latch area, “Cornell” collars, and tongue ties (although there is treadmill research evidence that suggests tongue ties are detrimental to DDSP). Medical therapies have included oral astringents, throat injections, throat sprays, systemic anti-inflammatory medications, and of course, surgery. The two most successful surgeries for DDSP are the “Llewellyn Procedure”, introduce in 1997 by Dr. H.R. Llewellyn from Ontario, Canada, and the “Tie-Forward Procedure” introduced by Dr. N.G. Ducharme from Cornell University in 2005. By some accounts these surgeries improve 95% of all DDSP horses and in one study, using USTA race records, by Dr. Llewellyn, showed improved race times of 2.5 seconds. Talk to your veterinarian at Brenford Animal Hospital about endoscope exams for horses suspected of suffering from DDSP. Try equipment changes and consider medical solutions. If not successful, consider one of these surgical procedures to prevent the poor performance caused by DDSP. -PFH (12.12.14)