Abstract
Endoscopy of thoroughbred (TB) yearlings at public auctions is common in South Africa. Laryngeal function (LF) is a common concern of buyers of young TBs. Cancellation of sale because of LF abnormalities is a concern for both the vendor and the buyer, with recurrent laryngeal neuropathy (RLN) being a common cause of sale cancellation. The aim of this descriptive study was to determine the prevalence of RLN at South African premier TB yearling sales. This study was designed as a retrospective descriptive analysis of upper respiratory tract (URT) endoscopic examinations to determine RLN grade, performed at two premier TB yearling sales in South Africa. Results of buyer-requested endoscopic examination from 2013 to 2019 were included. Results from the yearling sales were analysed for prevalence of RLN grade (using Rakestraw’s 4-point system) and compared to similar previously published studies. For analysis of effects of gender on RLN grading, horses were grouped and Fisher’s exact test was used to determine if there was a relationship between gender and grade. For comparison of the effects of age on grade, and sales year on grade, a Kruskal–Wallis test was conducted. A value of p < 0.05 was considered significant. A total of 858 horses were examined out of 4149 offered for sale; there were 57.58% colts and 42.42% fillies (mean age of 18.1 months). The annual percentage for grade 1 was 84.04% ± 9.98%, for grade 2: 14.49% ± 10.69%, for grade 3: 0.71% ± 0.57% and for grade 4: 0.76% ± 0.94%. There were no other significant findings. The exclusive nature of the sale and the increasing proclivity for pre-sale scoping may have skewed the results. This study shows that RLN grade incidences in TB yearlings at public auctions in South Africa are as follows: grade 1: 84.04%, grade 2: 14.49%, grade 3: 0.71% and grade 4: 0.76%. The results were similar to that of an adult population of horses examined in South Africa in a previous study.
Highlights
Endoscopy of thoroughbred (TB) yearlings as part of the yearling sale procedure is common in South Africa
Analysis of the effects for gender on recurrent laryngeal neuropathy (RLN) grading showed no significant difference between colts and fillies with grades 1 and 2 or with grades 3 and 4 RLN (Table 4)
The results of this study are, surprisingly, highly comparable to that of previous studies on older racehorses within South Africa (Saulez & Gummow 2009:431–435), with the only major difference being the percentage of grade 2 horses (14.49% compared to 1.8%)
Summary
Endoscopy of thoroughbred (TB) yearlings as part of the yearling sale procedure is common in South Africa. 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 grades 1 and 2 RLN showed significantly better racing performance as adults compared to yearlings with grade 3 RLN (Stick et al 2001:962–967). Loss of abduction and the resultant increased negative pressure in the laryngeal lumen during exercise result in inward collapse of the arytenoid, leading to increasing obstruction of the upper respiratory tract (URT), and can lead to poor performance (Kelly 2016)
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