'Roarers': Surprise Results for Horses Racing Post-Surgery

Roaring, or laryngeal hemiplegia, describes a condition in horses in which one side of the larynx (voice box) becomes paralyzed. Thoroughbreds and draft horses are more commonly affected, with reports suggesting up to 64% and 42% of those breeds, respectively, have varying degrees of hemiplegia.

“Because the paralyzed side of the larynx droops down into the airway of exercising horses, these animals produce a characteristic ‘roaring’ sound, prompting further evaluation,” said Ali Broyles, DVM, Dipl. ACVS (Large Animal), currently with Equine Sports Medicine and Surgery, in Weatherford, Texas. “The test of choice is endoscopy, which involves passing a camera through the nasal passages to directly view the back of the throat and larynx.”

Based on what a veterinarian observes during that endoscopic examination, a grading system introduced in 2003 helps categorize horses based on degree of paralysis. A grade of I describes horses with no abnormalities. Those with a maximum grade of IV have complete paralysis of laryngeal components, including the arytenoid cartilages and vocal folds.

“The treatment goal for horses diagnosed as roarers is to open the airways, ensuring the arytenoid cartilages and vocal folds no longer droop,” said Broyles.

Several surgical procedures can achieve this goal, including a combination of laryngoplasty and ipsilateral ventriculocordectomy or LPVC. This procedure involves using suture material to permanently “tie back” the floppy side of the larynx (arytenoid cartilage) and remove the soft tissues underneath the cartilage called the ventricle and vocal cord.

“It has long been though that a surgeon should wait until the arytenoid is completely paralyzed—which corresponds to grade IV disease—to perform a tieback surgery, because residual movement of the arytenoid might cause loosening of the suture material,” said Broyles.

To determine if horses that are not fully paralyzed would benefit from a tieback and ventriculocordectomy, Broyles and a team of U.S. researchers performed a study that she presented at the 2019 Annual American Association of Equine Practitioners Convention, held Dec. 7-11 in Denver. Together, they collected medical and race records of Thoroughbreds with grade III.1, III.2, III.3, and IV roaring. Grade of disease was based on the Havemeyer scale, summarized here:

All grade III horses have arytenoid cartilage movements that are asynchronous and/or asymmetric. Full arytenoid cartilage abduction cannot be achieved and maintained.

Grade III.1: There is asymmetry of the rima glottidis (the opening between the vocal cords and the arytenoid cartilages) much of the time due to reduced mobility of the arytenoid and vocal fold, but there are occasions, typically after swallowing or nasal occlusion, when full symmetrical abduction occurs but is not maintained.

Grade III.2: Obvious arytenoid abductor deficit and arytenoid asymmetry. Full abduction is never achieved.

Grade III.3: Marked, but not total arytenoid abductor deficit and asymmetry with little arytenoid movement. Full abduction is never achieved.

Key findings Broyles reported include:

  • Horses with Grade III.2 and III.3 had a 1.83 times higher chance of returning to racing than horses with Grade IV;
  • Horses with Grade IV required more time to return to racing compared to the Grade III horses; and,
  • Grade of laryngeal hemiplegia didn’t influence a horse’s average postoperative race earnings.

“In sum, grade IV horses took longer to return to racing and had a lower rate of return to racing than grade III.2 and III.3, which was an unexpected finding,” said Broyles. “Thus, it appears prudent to recommend a tieback on horses with residual movement of the arytenoid cartilage, and there may be some benefit in performing the procedure earlier in the disease process than traditionally thought. Overall, the LPVC remains the best treatment option for horses with grade IV disease.”