Surgery to correct "roaring" in National Hunt Thoroughbred racehorses can restore racing performance to levels similar to a matched group of peers in the short term, but career longevity appears to be negatively impacted following these procedures, report a team of UK researchers led by Safia Barakzai, BVSc, MSc, DESTS, Dipl ECVS, from the Royal (Dick) School of Veterinary Studies at the University of Edinburgh, Scotland.
"Roaring" is caused by dysfunction of the left recurrent laryngeal nerve, resulting in either partial or complete paralysis of the left arytenoid cartilage. Subsequently, the affected left cartilage droops into the lumen of the larynx where it obstructs the flow of air. The treatment of choice is laryngoplasty (i.e., "tie-back" surgery), which involves placing one or more sutures (stitches) to abduct the anomalous arytenoid cartilage, rendering the laryngeal lumen permanently open on one side.
"Compared to Thoroughbreds that race on the flat, National Hunt Thoroughbreds run over longer distances (2-4.5 miles) and also jump hurdles or fences," Barakzai explained.
Because the efficacy of laryngoplasty in National Hunt horses was not known, Barakzai and colleagues analyzed race records for 63 National Hunt Thoroughbreds and 126 race-matched controls to evaluate the effect of laryngoplasty and ventriculocordectomy (removal of the left vocal cord and saccule) on short- and long-term racing performance.
Barakzai and colleagues found that:
- 78% of horses raced post-operatively;
- 47% of horses improved their individual performance post-operatively;
- Affected horses earned less prize money in the five pre-operative races compared to control horses, but no difference in prize money earned was noted in the five post-operative races, and
- Affected horses started in significantly fewer lifetime races both before and after surgery compared to control horses.
The authors also reported that degree of surgical abduction of the left arytenoid cartilage in National Hunt Thoroughbred racehorses is not associated with post-operative success.
"Horses with grades 1-3 laryngeal abduction can race successfully, but we had too few horses with poor abduction (grades 4 and 5) to assess the effect of these grades on racing performance. Horses with maximal (grade 1) surgical abduction of the arytenoid cartilage immediately after surgery are significantly more likely to suffer post-operative loss of abduction than horses with grade 3 abduction immediately after surgery" said Barakzai.
"This finding suggests that surgeons should not be overly disillusioned by the appearance of only moderate (grade 3) abduction in the long term after LP surgery in racehorses, because most horse with grade 3 laryngeal abduction can race successfully," Barakzai said.
The studies, "Race performance after laryngoplasty and ventriculocordectomy in National Hunt racehorses," and, "Postoperative race performance is not correlated with degree of surgical abduction after laryngoplasty in National Hunt Thoroughbred racehorses," were both published in the December edition of the journal Veterinary Surgery.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.