The Prevalence of Abnormal Breathing Patterns During Exercise and Associations with Dynamic Upper Respiratory Tract Obstructions

Abstract

IntroductionDuring canter and gallop most horses maintain a locomotor‐respiratory coupling (LRC) ratio of one breath every stride. Occasional big respiratory cycles (BRC) are described when a single breath is taken over two strides. This is considered a transient but normal feature of ventilation. However, a change to a more persistent 2:1 LRC ratio is considered to be ‘abnormal’. It has been suggested that upper respiratory tract (URT) disorders could result in a horse adopting an abnormal breathing pattern, although current information is limited.MethodsSimultaneous audio and URT endoscopy recordings from 365 horses referred for treadmill evaluation were analysed. Breathing pattern at canter and gallop was categorised at each one minute speed step: Normal: 1:1 with <2 BRC Normal: 1:1 with 2 BRC Abnormal: breathing pattern disrupted by repetitive and frequent BRC's Abnormal: alternating between periods of 2:1 and 1:1 Abnormal: 2:1 throughout Data analysis was performed using PASW 18.0. A chi‐square test was used to identify associations between breathing pattern and presence of URT obstructions.ResultsDuring the entire exercise test 30% of horses had an abnormal breathing pattern at canter or gallop, of which 23% had a 2:1 breathing pattern. The prevalence of abnormal breathing patterns was higher at low canter speeds than during strenuous exercise. There was a significant association between breathing pattern during strenuous exercise and the presence of an URT obstruction (P = 0.008).ConclusionsLoss of a 1:1 LRC ratio during canter and gallop is more common than previously realised and may be associated with dynamic URT obstructions.Ethical Animal ResearchRetrospective analysis of case records. Sources of funding: none declared. Competing interests: none.