The Effect of Loading Upon Hoof Wall Growth and Hoof Shape in the Thoroughbred Foal
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The effect of loading upon hoof wall growth and hoof shape in the Thoroughbred foal by Simon John Curtis A thesis submitted in partial fulfilment for the requirements of the degree of Doctor of Philosophy at the University of Central Lancashire in collaboration with Myerscough College February, 2017 Declaration Concurrent registration for two or more academic awards: I declare that while registered as a candidate for the research degree, I have not been a registered candidate or enrolled student for another award of the University or other academic or professional institution. Material submitted for another award: I declare that no material contained in the thesis has been used in any other submission for an academic award and is solely my own work. Signature of Candidate; Type of Award; Doctor of Philosophy School; School of Sport and Wellbeing i Abstract The hoof wall is adapted to take most of the weight-bearing of the foot and is anisotropic and homogeneous. Foals appear to be born with symmetrical paired feet which by maturity are frequently unequal in angle and width. They stand within minutes of birth subjecting the hoof wall to loading. Hoof growth rate and hoof compression may be factors affecting hoof shape. The effect of conformation changes during maturation upon loading and differential hoof growth was unknown. The aims were to; quantify and evaluate the epidermal structure, hoof growth rate, hoof renewal, dorsal hoof wall angle, plastic hoof compression, and hoof loading, during paediatric development. Hoof growth rate, renewal, and hoof angle were recorded in foals (n=80) and weanlings/yearlings (n=12) and the hoof wall structure of histological samples of fetuses and paediatric foals (n=15) was determined. Solar loading, hoof growth, and hoof angle was recorded in healthy foals (n=18) and compared to a group with acquired flexural deformity (n=9). Horn tubule size and number increased significantly, and density decreased significantly during maturation. The dorsal hoof wall angle declined with age. Hoof renewal in newborn foals was 145±15 days whereas weaning/yearlings were 283±26 days. A relationship between plastic hoof compression and time was found (r = 0.46, P = 0.002). Hoof compression in foals was 0.039±0.022mm per day and in weanling/yearlings 0.03±0.016mm per day. Hoof growth rate, hoof compression, and dorsal hoof wall angle, all correlated to ageing and differed between the healthy and acquired flexural deformity foals. The original findings in this thesis give a broad understanding of the developing equine hoof wall. Knowledge of renewal times allows predictions of healing in cases of partial hoof wall avulsion. Original data recording the structure of the developing hoof wall may lead to a greater understanding of its response to loading, while improved recognition of the angles of the digit and hoof during maturation will allow a more accurate assessment of conformation. Hoof distortion is affected by loading, hoof compression and hoof growth and comprehending the link between these factors may lead to enhanced treatment strategies for all ages of horse. ii Table of Contents Declaration ........................................................................................................ i Abstract ............................................................................................................ ii Table of contents ............................................................................................. iii Illustrations and tables ................................................................................... ix List of illustrations .......................................................................................... ix List of tables ................................................................................................... xi Acknowledgements ........................................................................................ xii Quote .............................................................................................................. xiii Abbreviations and definitions ....................................................................... xiv Abbreviations ................................................................................................. xiv Definitions ..................................................................................................... xv Chapter 1: Introduction ................................................................................... 1 1.1: Evolution ............................................................................................. 1 1.1.1: Integument .................................................................................... 1 1.1.2: Adaptation of the digital integument ............................................... 1 1.1.3: Evolutionary adaptation ................................................................. 2 1.2: Anatomy of the hoof wall ................................................................... 3 1.2.1: Hoof capsule shape ....................................................................... 3 1.2.2: The stratum externum .................................................................... 4 1.2.3: The stratum medium ...................................................................... 5 1.2.4: Tubular horn .................................................................................. 5 1.2.5:Tubular density ............................................................................... 6 1.2.6:The hoof at birth ............................................................................. 7 1.2.7:The stratum internum ...................................................................... 8 1.3: Conformation ...................................................................................... 8 1.3.1: Angles of the digit .......................................................................... 8 1.3.2: Maturation of angles ...................................................................... 9 1.4: Hoof Morphometrics ........................................................................ 11 1.4.1: Measurement equipment ............................................................. 12 1.4.2: Defining measurement points ...................................................... 12 1.4.3: Radiographic measurement ......................................................... 14 1.4.4: Radiological studies ..................................................................... 14 iii 1.4.5: Radiography and foals ................................................................. 15 1.4.6: Hoof renewal ............................................................................... 16 1.4.7: Plastic deformation ...................................................................... 16 1.4.8: Weight-bearing and load ............................................................. 17 1.4.9: Hoof wall structure ....................................................................... 17 1.4.10: Differential hoof growth .............................................................. 18 1.4.11: Hoof wear .................................................................................. 18 1.4.12: Farriery ...................................................................................... 18 1.4.13: Deformation of horn ................................................................... 19 1.4.14: Elasticity of horn ........................................................................ 19 1.4.15: Role of horn tubules ................................................................. 20 1.5: Hoof growth and hoof renewal ........................................................ 21 1.5.1: Hoof wall growth .......................................................................... 21 1.5.2: Hoof growth rate .......................................................................... 21 1.5.3: Hoof angle ................................................................................... 21 1.5.4: Hoof avulsion ............................................................................... 22 1.5.5: Hoof renewal from birth ............................................................... 22 1.6: Weight-bearing and loading ............................................................ 23 1.6.1: Photometry .................................................................................. 24 1.6.2: Visual assessment....................................................................... 24 1.7: Equine hoof development ................................................................ 25 1.7.1: Development of the hoof in utero ................................................. 25 1.7.2: Material properties of hoof horn ................................................... 27 1.7.3: Fracture toughness...................................................................... 27 1.7.4: Elastic deformation of hoof .......................................................... 28 1.7.5: Tendons of the equine leg ........................................................... 29 1.7.6: Hoof capsule shape change ........................................................ 29 1.7.7: Acquired flexural deformity of the distal interphalangeal joint....... 31 1.7.8: Weight distribution of the limbs .................................................... 32 1.7.9: Pressure mats ............................................................................. 33 1.8: The Thoroughbred breeding industry ............................................