With the 2011 OBS August Yearling Sale looming, I thought I would briefly discuss the prepurchase endoscopic examination in this article to shed some light on how thoughts have changed on the subject in recent years. Endoscopy (scoping) is used by veterinarians in the sales setting to examine the structures of the equine upper respiratory tract (URT).
It involves using a flexible, tubular, camera-like structure attached to a light source which is inserted into a nostril and passed up the nasal cavity until the throat is visible. The URT structures of interest include the soft palate, the epiglottis, and the arytenoid cartilages.
The soft palate comprises the caudal part of the roof of the mouth and the muscular floor of the pharynx; its normal position is in front of and below the epiglottis. Dorsal displacement of the soft palate occurs when the palate slips on top of the epiglottis to partially obstruct the airway.
This dorsal displacement can be seen in sales yearlings due to laryngeal spasm, but it will often readily correct itself during the examination and has no negative effect on future racing performance. The structure of the normal epiglottis has good length, thickness, and definition with serrated edges. Epiglottal entrapment can occur when the epiglottis becomes enveloped by a fold of mucosa arising between the epiglottis and the base of the tongue.
The arytenoid cartilages function as flaps that abduct (open) to facilitate airflow and adduct (close) to protect against feed contamination during swallowing. Laryngeal hemiplegia is a condition that occurs when nerve damage to one of the cartilages (usually the left) causes paralysis to that structure, thereby causing a lack of abduction of that flap.
Dr. Scott Pierce and Dr. Rolf Embertson of Rood and Riddle Equine Hospital in Lexington performed a study that was published in 2001 which followed 816 Thoroughbred yearlings through their racing careers at 2 and 3 years of age. The arytenoid function was graded using an I-IV scale.
Grade I, symmetrical and synchronous; Grade IIa, mildly asymmetrical or asynchronous with maximum abduction easily achieved; Grade IIb, asymmetrical or asynchronous with maximum abduction achieved with difficulty; Grade IIIa asymmetrical or asynchronous and movement cannot maintain full abduction; Grade IIIb limited movement but arytenoid cannot fully abduct; Grade IV, no arytenoid movement. The epiglottic structure was graded normal ((N) as described above) or 1-4 abnormal.
Grade 1, slightly flaccid with good length and texture; Grade 2, mild flaccidity, adequate length, thinner than normal curled edges, no dorsal vasculature; Grade 3, moderately flaccid, very thin and easily bent; Grade 4, severely flaccid, extremely thin, markedly short, and easily bent. The results of their study showed that there was no difference in racing performance for horses with Grades I, IIa, and IIb arytenoid symmetry at two or three years of age.
Horses with Grade III arytenoids had fewer starts and fever earnings than 3-year-olds. Yearlings with mild and moderate flaccid epiglottis had fewer starts and fever earnings as 2-year-olds but no difference as 3-year-olds.
The moral of the story is that there is no statistical difference between a Grade I throat and a Grade IIb throat when it comes to impact on future racing performance.
The Pierce and Embertson study showed that up to 98 percent of sales yearlings have “normal” throats, as most variations have no negative impacts on future performance. It is up to the experienced veterinarian to assess URT structures in the face of minor to moderate variations of normal and inform buyers of findings.
It is the buyer’s responsibility to take endoscopy findings into account as only one variable in the complex equation of whether or not to purchase a given yearling. One should not discard an individual if he/she does not possess a “perfect” throat.
- Pierce, S.W. and Embertson, R.M. Correlation of Racing Performance to Yearling Endoscopic Evaluation. 2001 AAEP Proceedings. Vol. 47. 113-114.
- Mitchell, Frank. Vet Work Plain & Simple: What Is Scoping? The Consignors and Commercial Breeders Association. Lexington, Kentucky. 2005.
