VETERINARY
New thoughts on thoroughbred throats
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It’s the roar of the crowds – not the roaring of his horses, that Kiaran McLaughlin, trainer of Invasor, 2007’s Horse of the Year, likes to hear. As any experienced trainer will testify, however, throat problems like “roaring” are all too common. Roaring is one the most common causes of respiratory-related poor performance in thoroughbreds, and has therefore attracted a great deal of interest from the equine community. Although surgeries for roarers were first attempted over 150 years ago, the success rate remains less than ideal. WORDS: Stacey Oke, DVM, MSc PHOtOS: ROBIN PeteRSON
MCLAUGHLIN admits he hasn’t had great luck with throat surgeries in the past. He lamented, “I just wish there was something else we could do.” Veterinary researchers and surgeons agree that improvements are needed, which drives them to seek solutions to owners’ and trainers’ pleas for better results. This article looks at the most up-to-date information on how best to diagnose and treat roaring. Novel, promising treatment options that can be used with the classic “tie-back” surgery are also discussed.
To roar or not to roar When you are standing on the rail in the morning, the sound of a roarer galloping past you is fairly distinctive. The sound is caused by the left arytenoid cartilage (see sidebars) drooping into the opening of the larynx. The underlying cause of the problem is dysfunction of the left recurrent laryngeal nerve. When that nerve fails to function properly, it stops signaling the left arytenoid cartilage to pull back during exercise. If a horse can’t move enough air to the lungs during exercise – in this case because the arytenoid cartilage is blocking
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airflow – they cannot perform their best. This is why roarers tend to fade or even stop during the latter part of a race. In contrast, the arytenoid cartilages in normal horses abduct fully to allow a large volume of air to move unobstructed through the throat.
In the eye of the beholder As easy as an abnormal arytenoid cartilage should be to recognize, it is not always a straightforward diagnosis. “It can be extremely challenging to diagnose the cause of the noise,” explained James C. Hunt Jr., DVM, a private practitioner at Belmont Park in New York. Over the course of Dr. Hunt’s 30-year career, he has scoped thousands of horses, including Curlin, Invasor, and Rags to Riches. Hunt said, “For starters, the horse usually needs to work or run at least five-eighths of a mile before fatigue occurs and the roaring sound can be heard. Most people don’t breeze farther than that, so if you’re relying on your ears to detect a problem, you’re going to miss a lot of roarers.” He went on to explain that a routine resting “scope” (examination of the horse’s throat with an endoscope) can only tell you so much.
“When vets scope, what we see is not always what is happening on the track. Even if they were making noise on the track, if we scope them right away the horse could be completely abducted. If you scope them again 30-40 minutes later then you may see the asymmetry,” said Hunt. By “asymmetry” Hunt means that the right and left arytenoid cartilages are not opening in an either equal or symmetric manner. “Scoping the horse on a treadmill or using a dynamic scope can give us a lot of information,” Hunt noted. Dynamic scoping involves breezing a horse with a scope in the horse’s airway. It is a valuable tool that allows veterinarians to record exactly how the throat is functioning under race conditions. Scoping on a treadmill also remains a viable option to help diagnose upper airway disorders that could be overlooked with standing (resting) endoscopy. In the right hands, ultrasound is another important diagnostic option. Cornell University researchers used ultrasound in 154 horses with a history of poor performance due to upper airway disease. In their report, scheduled to be published in an upcoming edition of the journal Veterinary Radiology and Ultrasound, the authors concluded, “…ultrasound offers