Effect of head and neck position on upper airway function in standardbred racehorses

Abstract

<jats:sec><jats:title>Introduction</jats:title><jats:p>Poll flexion may play an important role in the development of dynamic upper respiratory tract (<jats:styled-content style="fixed-case">URT</jats:styled-content>) collapse. However, limited investigations have been performed in Standardbred racehorses.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>Eight Standardbreds were examined during training, once flexed and once in extension, using a randomised crossover design. Head position was maintained using modified check‐reins and head‐neck angle was recorded. On each occasion horses performed 2 rounds of exercise of 2400 m at ∼35 km/h. Speed and heart rate (<jats:styled-content style="fixed-case">HR</jats:styled-content>) were measured and blood obtained before and after exercise. <jats:styled-content style="fixed-case">URT</jats:styled-content> endoscopy was performed during the second round. Videos were blinded and <jats:styled-content style="fixed-case">URT</jats:styled-content> function assessed. <jats:styled-content style="fixed-case">HR</jats:styled-content>, plasma lactate (Lac) and speed were compared for different head positions using paired t‐tests. Cortisol was analysed using repeated‐measures <jats:styled-content style="fixed-case">ANOVA</jats:styled-content> and <jats:styled-content style="fixed-case">URT</jats:styled-content> function using Fisher's exact tests and paired t‐tests (P&lt;0.05).</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Data were excluded for one horse where head‐neck angle could not be measured. Flexed and extended head‐neck angles differed significantly (mean: 85.0° vs 97.8°; P = 0.001). All horses showed some form of <jats:styled-content style="fixed-case">URT</jats:styled-content> collapse during exercise, although this was only deemed clinically significant in 4 horses with a history of abnormal noise. These horses showed additional abnormalities during flexion. However, mean severity scores did not reach statistical significance (P = 0.08). No significant difference was found for speed, <jats:styled-content style="fixed-case">HR</jats:styled-content> or Lac. A significant increase in cortisol was found with exercise (P&lt;0.001). The interaction between time and head position approached significance (P = 0.09) with higher concentrations of cortisol generally occurring in extension rather than flexion.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p><jats:styled-content style="fixed-case">URT</jats:styled-content> abnormalities may be exacerbated with poll flexion. The use of equipment to modify head position may induce a stress response.</jats:p></jats:sec><jats:sec><jats:title>Ethical Animal Research</jats:title><jats:p>This study was approved by the University of Adelaide Animal Ethics Committee and owner informed consent obtained. <jats:bold>Sources of funding:</jats:bold> University of Adelaide honours projects. <jats:bold>Competing interests:</jats:bold> none.</jats:p></jats:sec>