Cues for capturing the complexity of equine locomotion
Authors:   , Smit Ineke Hillie 
Published: March 2024

Locomotion is a fundamental part of life. The ability to move from one place to another enables animals to interact with their environment, making it an essential factor for natural behaviour, health and welfare. Hence, it is unsurprising that there has been an interest in how animals move since the very dawn of science. The approach towards the study of locomotion has followed the development of science in general. As such, in the days of Antiquity the approach was mainly observational and it was only after the Renaissance, with increasing means and technologies, that experimental studies slowly became mainstream. However, locomotion is incredibly complex and as a result, the scientific approach has been strongly reductionist in character. However, in the past decennia, we have seen an exponential growth of relevant technologies and computational power, which allows for an increase of the comprehensiveness of the traditional reductionist approach. With that, we can slowly try to further understand how locomotion truly works.

This thesis hopes to contribute to the development of an increasingly comprehensive approach to study locomotion. This is done by applying existing techniques to characterise differences between breeds, investigate less common gaits and explore how locomotor-related pain is expressed in different contexts. In addition, considerations to expand the methodological toolbox in the disciplines of both kinematics and muscle function are presented. The subject of this study is the horse, one of the rare species domesticated for its locomotor potential and, in terms of this potential, the most studied non-human animal species.

Chapter 2 highlights that no horse is the same in terms of their locomotion. Kinematic data of 65 horses of three different breeds were collected using IMUs to describe general differences in locomotion patterns between breeds while performing symmetrical gaits. Emphasis was placed on the Icelandic horse. We assessed timing of peak events and how they related to footfall patterns and mechanics of the different gaits.

Chapter 3 and 4 describe how Icelandic horses adapt to acute fore- and hindlimb lameness during both walk and trot, as well as tölt. The horses were assessed in hand as well as while ridden. Upper body movement and temporal changes in limb kinematics were assessed using IMUs.

In chapter 5, bilateral and more chronic hindlimb lameness in Shetland ponies is studied. Optical motion capture was used to capture full body kinematics during trot on a treadmill. In addition, continuous and discrete data analysis were compared to unravel the mechanics of adaptations to bilateral lameness.

Chapter 6 describes the effect of electrode location on electromyographic signal quality and activation patterns during trot on the treadmill. Twenty-one muscles were studied in three horses using linear arrays of electrodes.

Nature is complex and is best studied through collaborative and multidisciplinary networks. Therefore, chapter 7 is dedicated to open science. Several datasets are described that support the findings of this thesis.