The effect of the head and neck position on the equine athlete

Abstract

Over the last few years, the welfare implications of certain training techniques used in the horse industry have gained more attention from the general public. In Warmblood performance horses, this concern is focused on the use of a hyperflexed head and neck position, also named “rollkur”. The aim of this thesis is to measure the effect of 5 different head and neck positions on the equine athlete, in this study represented by the base level trained dressage horse. The first part of this thesis concerns an ex vivo study describing the use of contrast CT and MRI to visualize equine cervical spine anatomy and measure the ex vivo effect of flexion and extension on intervertebral foramina dimensions. The ex vivo part is followed by an in vivo study, measuring the effect of the head and neck position on three clinical areas, all influencing equine welfare: 1. The effect on neuromuscular functionality; 2. The effect on upper airway functionality and 3. The effect on indicators of stress. The head and neck positions were defined as follows: HNP1-Unrestrained (control), HNP2-Neck raised, bridge of nose around the vertical. HNP4-Neck lowered and considerably flexed, bridge of nose pointing towards the chest. HNP5-Neck raised and considerably extended, bridge of nose in front of the vertical. HNP7-Neck lowered and flexed, bridge of nose pointing towards the carpus. Seven base level trained dressage horses were accustomed to the different positions for at least 3 weeks, before the start of the study. During the actual study, the horses were exercised on the lunge in an exercise protocol consisting of trot(1) (10 min), canter (4 min), trot(2) (5 min) and walk (5 min). Neuromuscular transmission was measured with quantitative (SF)EMG and muscle enzyme concentrations and indicated an effect of every head and neck position compared with HNP1, but the most significant effect was seen in HNP4. Upper airway functionality was measured with an esophageal pressure balloon and arterial blood gas values. This study again demonstrated an effect in each position compared with HNP1, but an inspiratory upper airway obstruction developed in HNP4, without an effect on arterial blood gas values. Behavioural observations, blood and saliva cortisol concentrations and heart rate variability were measured as indicators of stress, which demonstrated more conflict behaviour in the extended positions (HNP2 and HNP5). This thesis significantly contributes to the understanding of the effect of different head and neck positions on the equine athlete. Based on the results of this study, it might be argued that if the use of a flexed position is desired, HNP7 may be preferable over HNP4 in the base level trained dressage horse.