Association between "wind-test" findings and resting endoscopic assessment of laryngeal function at Thoroughbred Public Auction in the UK

Reasons for performing study:

Despite ongoing advances in diagnostic imaging, ‘wind-testing’ remains the most common screening test for upper respiratory tract obstructions and is an important condition of sale at Thoroughbred public auctions in UK/Europe. Correlations between abnormal respiratory noise and resting laryngeal function have been incompletely investigated to date.

Objectives:

To determine whether associations exist between respiratory noise at lunge and subsequent diagnosis of recurrent laryngeal neuropathy (RLN).

Study design:

Retrospective analysis of records for all post sale wind-testing undertaken by a single veterinary practice at Tattersalls Newmarket yearling, breeze-up and horse-in-training sales between 2009 and 2013.

Methods:

Descriptions of abnormal respiratory noise were categorised as ‘inspiratory whistle’, ‘inspiratory harsh’ or ‘pan-respiratory harsh’, and included lunge direction during which noise was evident. Concurrent examination by 2 veterinary surgeons was a criterion for inclusion of cases. All horses making abnormal respiratory noises underwent resting endoscopy with a consensus score (Lane scale) given for laryngeal function.

Results:

2972 horses underwent post sale wind-testing and 418 horses (14.1%) underwent resting endoscopic examination due to abnormal respiratory noise. Likelihood of making an abnormal respiratory noise differed significantly between groups (yearlings 10.8%, ‘breeze-up’ 2-year-olds 20.6%, horses-in-training 30.1%). Yearlings were significantly more likely (P<0.0001, Chi-squared/Bonferroni test) to make a ‘harsh’ respiratory noise than horses-in-training. Type of noise (whistle) was significantly associated with resting endoscopic evidence of RLN in yearlings (P = 0.009); specificity of ‘whistle’ for RLN in this group was 38.6%. There was no association between lunge direction noise (left, right or both) and RLN.

Conclusions:

These results support the widespread belief that harsh respiratory noise when lunged of presumed ‘palatal/pharyngeal’ origin is more likely in yearlings than horses-in-training, possibly due to upper respiratory inflammation or immaturity. Inspiratory whistle in both lunge directions is no stronger an indicator of RLN than unidirectional whistle.