The Young Horse Upper Airway

It has become commonplace for an upper respiratory tract (URT) endoscopy to be performed at pre- and post-sale examinations of young horses--especially at Thoroughbred sales. To address what is normal and what is abnormal, Rolf M. Embertson, DVM, of Rood & Riddle Equine Hospital in Lexing-ton, Ky., studied Thoroughbred weanlings and yearlings and compared those findings to URTs of adult horses, those over two years of age. According to Embert-son, "It's important to realize during upper respiratory tract (URT) evaluation of the weanling and yearling that there are subtle differences when compared to the adult horse. It can be difficult to predict future pharyngeal and laryngeal function based on one endoscopic exam of the URT of the weanling and yearling."

Basing his study on Thoroughbreds, Embertson added that young horses' throats change with age. He said many young horses with questionable looking throats end up performing fine as racehorses, while others which have normal-looking throats end up with problems on the track.

Embertson said, "When compared to the mature horse, the immature horse generally has a higher grade of pharyngeal lymphoid hyperplasia (PLH); a shorter, narrower, and more flaccid epiglottis; and an increased incidence of dorsal displacement of the soft palate (DDSP) when the URT is stressed by nasal occlusion. The immature horse occasionally will have a row of small raised bumps on dorsal midline of the epiglottis. The younger the horse, the more often this is seen."

Embertson believes this variation falls within what is considered normal. He added, "arytenoid movement is not as consistent and repeatable in the immature horse. Most of the subtle differences between immature and mature horses gradually disappear with age."

In Thoroughbreds, the differences usually disappear by the end of the second year, based on Embertson's observations.

According to Embertson, an upper respiratory tract endoscopic exam is performed on about 80% of the Thoroughbreds going through the sales arenas in Lexington, and in many cases, horses will have even further examinations performed on them. To address issues of abnormalities found in young sale horses, Fasig-Tipton and Keeneland sales companies have listed the following conditions as reasons for allowing the return of any yearling sold after July 1: laryngeal hemiplegia, rostral displacement of the palatopharyngeal arch, epiglottic entrapment, permanent dorsal displacement of the soft palate, severe arytenoid chondritis or chondroma, sub-epiglottic cyst, and cleft palate.

In order to avoid dilemmas in purchasing a young horse, many veterinarians encourage buyers to conduct pre-sale URT exams since there are some conditions that might be acceptable according to the conditions of sale, but do not meet the veterinarian's criteria for being acceptable, according to Embertson.

He adds, "A very small percentage (less than 2%) of the yearlings at the Keeneland and Fasig-Tipton sales are found to have one of the listed unacceptable conditions during the pre-sale or post-sale URT exam. However, a slightly higher percentage of yearlings with one of the unacceptable conditions would be found in the general (horse) population."

The reason for this is that many sellers will have a URT exam performed on horses before they are shipped to the sale. By doing so, the seller has the knowledge that the horse has passed the URT exam if the buyer decides to follow through with one.

Embertson pays particular attention to whether a young horse has a partially paralyzed arytenoid and whether the horse has a small and flaccid epiglottis. This is a concern to him because this condition could predispose that horse to a dorsal displaced soft palate (DDSP) as a racehorse.

Further abnormalities that can be found in yearlings after performing a URT exam include problems in the nasal passages, pharynx, and larynx. These abnormalities might manifest themselves in the form of epidermal inclusion cysts (atheroma), a malformed nasal septum, or maxillary cysts in the nasal passage. In the pharynx, problems such as pharyngeal lumen size, pharyngeal lymphoid hyperplasia (PLH), DDSP, cleft palate, and rostral displacement of the palatopharyngeal arch occasionally are seen. The larynx lends itself to problems with the size and stiffness of the epiglottis, an entrapped epiglottis, a sub-epiglottic cyst, in arytenoid movement, and in arytenoid chondropathy (small reddened areas occasionally seen on the corniculate process or near the vocal process of the arytenoid).
Many of these problems are rare in the young horse, and in some cases the young horse may outgrow the problem when it matures. In other cases proper treatment will allow the horse to go on to a successful racing career.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.