Heritability analyses of musculoskeletal conditions and exercise-induced pulmonary haemorrhage in thoroughbred racehorses

Welsh, Claire Elizabeth (2014) Heritability analyses of musculoskeletal conditions and exercise-induced pulmonary haemorrhage in thoroughbred racehorses. PhD thesis, University of Glasgow.

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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.
iii
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.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Thoroughbred, musculoskeletal, EIPH, horse, genetic, epidemiology, heritability
Subjects: Q Science > QH Natural history > QH426 Genetics
S Agriculture > SF Animal culture > SF600 Veterinary Medicine
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Veterinary Medicine
Supervisor's Name: Parkin, Dr. Timothy D. H. and Mellor, Prof. Dominic
Date of Award: 2014
Depositing User: Dr Claire Elizabeth Welsh
Unique ID: glathesis:2014-4862
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 06 Feb 2014 11:27
Last Modified: 06 Feb 2014 13:19
URI: http://theses.gla.ac.uk/id/eprint/4862

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