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In recent years one can observe more and more frequently the use of hyperflexion, the so-called "rollkur" at ridden horses in education, training, but also in competitions.
The aim of this study was on the one hand, in a preliminary study, to test the applicability of the overground endoscopy under natural training conditions and on the other hand, in the main study, to investigate the effects of different head-neck-positions on endoscopic findings of the upper respiratory tract and stress parameters in the ridden horse.
In the preliminary study a total of 30 horses of different types of use were examined. One-third were each gallop racing horses, trotters and riding horses. The horses were investigated in their natural environment under real training conditions with the overground endoscope. The behaviour during the application of the equipment and during the investigation was documented and the endoscopic images were recorded. Later, these were evaluated with regard to their picture quality and ease of interpretation. Overall, the study was very well practicable in most horses. Four horses showed strong defensive movements during insertion of the endoscope and in three of these horses the investigation had to be cancelled. The remaining horses were all trainable with the inserted endoscope, only one horse has shown slight head shaking during exercise. Two horses have developed slight nosebleeds during investigation. The quality of images was high enough to evaluate findings of the upper respiratory tract. The preliminary investigation has revealed that the new technique of overground endoscopy is an available option to examine horses under natural training conditions endoscopically. The application has been practicable in the field and most of the horses have tolerated the investigation.
Furthermore goal of the present study was a comparison between the impacts of different head-neck-positions on findings in the upper respiratory tract of ridden horses.
For this purpose video recordings of the larynx of 14 horses were recorded using the above mentioned overground endoscope. The videos were recorded at rest and during three different riding phases: first at stretching posture, secondly at a working head-neck-position and thirdly at hyperflexion. In comparison between the phases working head-neck-position and hyperflexion the analysis revealed a significant reduction of the laryngeal opening area (p = 0.001) with a value of 8.2 ± 5.0%. Beyond that, other evaluated parameters of the larynx, except its height, showed a significant diminishment as well. These changes did not correlate with the age of the horses or their level of education and they were independent of the individual anatomic conditions of the head-neck region. Capitulatory it can be stated that hyperflexion has caused a considerable compression of the larynx.
In the present study the influence of different head-neck-positions on stress parameters were investigated, too. In 18 horses heart rate, heart rate variability (HRV) and blood cortisol levels were measured. Values were recorded at rest, while riding with a working head-neck-position and while riding in hyperflexion of the horses’ head and neck.
In addition rideability and behaviour during the different investigation stages were evaluated by the rider and by an observer. The heart rate (HR) as well as the HRV did not show a significant difference between working head-neck-position (HR=105±22/min; LF/HF=3.89±5.68; LF=37.28±10.77%) and hyperflexion (HR=110±18; LF/HF=1.94±2.21; LF=38.39±13.01%). LF and HF are power components which show the behaviour of the two branches of the autonomic nervous system in the frequency domain measurement of HRV (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996). These parameters show the current activity of the sympathetic and parasympathetic nervous system. They can serve as stress parameters.
However, in comparison between working head-neck-position (158±60nmol/l) and hyperflexion (176±64nmol/l, p=0.01) blood cortisol levels revealed a significant increase.
This could be interpreted as an indication of stress. The survey and evaluation of rider and observer have resulted in a significant change of rideability to the worse in all collected parameters between working head-neck-position and hyperflexion.
Thereby indications to stress and adverse effects on wellbeing have appeared.
This study has clearly shown that the use of overground endoscopy technique could be used quite well with little on-site staff in most horses and has delivered high-quality images.
In conclusion, the results of the study have shown that the hyperflexion has led to a significant compression of the larynx and this has taken place regardless of the individual form of the head-neck region of the single horse.
The evaluation of rider and observer has revealed that horses have shown signs of stress during hyperflexion and negative effects on their well-being.
Nevertheless many parameters can`t be optimal objectified and standardized in a clinical trial with horses that are ridden under natural conditions.
To examine the effects of head-neck-position even more, further studies with larger numbers of animals are needed. The focus on the impact of head-neck-position and hyperflexion especially on the upper respiratory tract would be interesting.
Further studies could measure the air flow by means of pressure probes and could allow conclusions regarding to the hyperflexion-associated narrowing of the larynx, if it leads to strong turbulences, which could increase the respiratory rate and possibly the total pressure.
Also it could be investigated in the future whether lower airway diseases and chronic obstructive changes could be favoured under certain circumstances. Furthermore, the impact of the narrowing of upper airway tract on the arterial blood gas parameters has to be examined. Such studies could clarify whether there could be a reduced oxygen partial pressure and reduction in performance by hyperflexion or may explain this.
Overall, in future such studies could help to prove scientifically whether the hyperflexion impairs the well-being and health of our horses or not.