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Heritability Analyses of Musculoskeletal Conditions and Exercise-Induced Pulmonary Haemorrhage in Thoroughbred Racehorses

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Heritability Analyses of Musculoskeletal Conditions and Exercise-Induced Pulmonary Haemorrhage in Thoroughbred Racehorses View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Glasgow Theses Service Welsh, Claire Elizabeth (2014) Heritability analyses of musculoskeletal conditions and exercise-induced pulmonary haemorrhage in Thoroughbred racehorses. PhD thesis. http://theses.gla.ac.uk/4862/ Copyright and moral rights for this thesis are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given. Glasgow Theses Service http://theses.gla.ac.uk/ [email protected] Heritability analyses of musculoskeletal conditions and exercise-induced pulmonary haemorrhage in Thoroughbred racehorses By Claire Elizabeth Welsh BVMS (Hons) MSc (VetSci) AHEA MRCVS A thesis submitted for the degree of Doctor of Philosophy School of Veterinary Medicine College of Medical, Veterinary and Life Sciences University of Glasgow January 2014 ABSTRACT Musculoskeletal conditions and exercise-induced pulmonary haemorrhage are commonly diagnosed in Thoroughbred racehorses worldwide, and have serious consequences for racehorse welfare and the racing economy. Despite increasing interest in the study of genetic susceptibility to disease from the veterinary research community as a whole over past decades, the Thoroughbred has been largely ignored as a study group. The availability of software capable of complex genetic analyses using large, unbalanced pedigrees has made the study of genetic susceptibility to disease a realistic prospect for veterinary researchers. This study aimed to complete preliminary analyses of the genetics of a number of important musculoskeletal conditions, and of exercise-induced pulmonary haemorrhage, in two different Thoroughbred populations. Multivariable regression analyses were performed to identify important environmental risk factors for each condition in each population, and heritability analyses were conducted. Genetic correlations between disease conditions were also investigated. Fracture, tendon injury, suspensory ligament injury, osteoarthritis and EIPH/epistaxis were found to be heritable traits in the Hong Kong population. Distal limb fracture, SDFT injury and epistaxis were also found to be heritable in the UK Thoroughbred population. Most heritability estimates were small or moderate in magnitude. Selective breeding strategies that identify those animals with low genetic risk could play a part in future efforts to reduce the incidence of these conditions, in conjunction with favourable environmental manipulations based on research evidence. Due to low heritability, most of the conditions studied here would reduce in incidence slowly if selective breeding were implemented, thus strategic environmental manipulations would be warranted alongside such longer-term efforts to provide effective incidence reductions. A number of conditions were found to be positively genetically correlated, suggesting that risk reduction through breeding could reduce the risk of multiple diseases concurrently. For example, fracture and osteoarthritis were found to be positively genetically correlated (0.85 – 0.89) in the Hong Kong racehorse population. However, using the Hong Kong Thoroughbred population dataset, EIPH/epistaxis and tendon injury were negatively genetically correlated, which suggests that reduction in genetic risk of one of these may lead to increased genetic risk of the other. ii Measures of the durability and performance of racehorses were investigated to assess whether they were heritable traits in the UK and Hong Kong racehorse populations, and to assess their relationship to the disease conditions studied. Selection based on more holistic measures of horse health and longevity such as ‘career length’ could be a more attractive prospect for stakeholders, as this could forego the need to select for many different traits individually. Career length, number of starts over the career, and the level of earnings were all heritable traits in both populations. These holistic traits were found to have variable relationships with the disease conditions studied in each population. These analyses are the first to assess the genetic contribution to risk for many important diseases in the Thoroughbred. They provide a starting point from which further investigations into the applicability of genetic manipulations could yield realistic and achievable tools for racing stakeholders to use to ‘improve’ the breed in future. iii TABLE OF CONTENTS ABSTRACT ...................................................................................................................................................... II TABLE OF CONTENTS .................................................................................................................................... IV LIST OF TABLES ............................................................................................................................................ VIII LIST OF FIGURES ........................................................................................................................................... XIII ABBREVIATIONS .......................................................................................................................................... XVI ACKNOWLEDGEMENTS .............................................................................................................................. XVII AUTHOR’S DECLARATION .......................................................................................................................... XVIII 1. CHAPTER I. INTRODUCTION .............................................................................................................. 1 1.1 GENERAL INTRODUCTION ............................................................................................................................ 2 1.2 HORSERACING AND THE THOROUGHBRED .......................................................................................................... 3 1.2.1 Horseracing industry ........................................................................................................................ 3 1.2.1.1 United Kingdom horseracing .................................................................................................................... 3 1.2.1.2 Hong Kong horseracing ............................................................................................................................. 7 1.2.2 Injuries sustained during racing and training .................................................................................. 8 1.2.2.1 Overview ................................................................................................................................................... 8 1.2.2.2 Fracture ................................................................................................................................................... 10 1.2.2.3 Musculoskeletal injury ............................................................................................................................ 12 1.2.2.4 Exercise-induced pulmonary haemorrhage and epistaxis ...................................................................... 14 1.3 EQUINE GENETICS ....................................................................................................................................... 16 1.3.1 The Thoroughbred ......................................................................................................................... 16 1.3.2 Genetic diseases of the domestic horse ......................................................................................... 17 1.3.2.1 The genetics of fracture .......................................................................................................................... 18 1.3.2.2 The genetics of musculoskeletal conditions ........................................................................................... 19 1.3.2.2.1 Osteoarthritis and osteochondrosis ............................................................................................... 19 1.3.2.2.2 Tendon conditions .......................................................................................................................... 20 1.3.2.2.3 Ligament conditions ....................................................................................................................... 20 1.3.2.3 The genetics of EIPH ............................................................................................................................... 21 1.3.3 Genetic concepts and their applications ........................................................................................ 21 1.3.3.1 Heritability .............................................................................................................................................. 21 1.3.3.2 Genetic correlations ................................................................................................................................ 24 1.3.3.3 Genomic selection .................................................................................................................................
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