EQUINE | URT endoscoping
Endoscopic Recurrent Laryngeal Neuropathy Grade
Prevalence in a Sample of Thoroughbred Yearlings at
Public Auction in South Africa (2013-2019)
Reproduced with kind permission if the Journal
of the South African Veterinary Association
https://doi.org/10.4102/jsava.v91i0.2013
Introduction
Endoscopy of Thoroughbred (TB) yearlings as part of the
yearling sale procedure is commonplace in South Africa.
Laryngeal function (LF) is a common concern of potential
buyers of young TBs worldwide. The main concern for
buyers is to identify abnormal function of an arytenoid
(usually the left) before conclusion of the sale, allowing
the buyer to cancel the sale and avoid purchasing a horse
with recurrent laryngeal neuropathy (RLN), avoiding
potential poor performance and obviating the need for
future surgical intervention. This concern is justified as
it has been shown that TB yearlings with grade 1 and
2 RLN had significantly better racing performance as
adults, compared to yearlings with grade 3 RLN (Stick et
al. 2001:962–967).
There are multiple problems that can affect RLN. One
of the most common presents as laryngeal hemiplegia.
This is the loss of abduction of the arytenoid cartilage,
most commonly the left. Loss of abduction and
resultant increased negative pressure in the laryngeal
lumen during exercise results in inward collapse of the
arytenoid leading to increasing obstruction of the upper
respiratory tract (URT) and can lead to poor performance
(Kelly 2016).
In a United Kingdom (UK) study of 197 TB foals, the
prevalence of laryngeal asymmetry was 19% with grade
3 or 4 and when 187 of these that were re-examined
as yearlings, 23% were grade 3 or 4 (Lane 2004:31-
32). Studies showing comparative prevalence of RLN
grading are shown in Table 1. The reasons for the wide
variation seen in the prevalence in each study may be
attributable to a number of factors including the life
stage the horses were examined (yearlings vs adults),
exercise stage (at rest or immediately post racing),
differences in the observers’ definition of arytenoid
asymmetry, experience of the observer, selection criteria
for endoscopic examination and the grading scale used.
In a retrospective dynamic over-ground endoscopy
study in South Africa, abnormal arytenoid function at
exercise, consistent with laryngeal hemiplegia, was
detected in 33% of the TB race horses (Mirazo et al. 2014).
However, this study only included horses specifically
referred for further diagnosis of poor performance
or respiratory noise and, as such, the prevalence of
detectable problems may be higher than in the general
population. The study does compare well to other studies
of Thoroughbred racehorses which mainly included
those referred for investigation of respiratory noise and/
or poor performance of approximately 8% – 40% of
horses (Allen & Franklin 2010:186–191; Barakzai & Dixon
2011:18–23.; Dart et al. 2001:109–112; Desmaizieres et
al. 2009:347–352.; Tan et al. 2005:243–248).
In another South African cross-sectional study looking
at post racing prevalence of URT disorders in horses
24 • Equine Health Update •