Sport horses: breeding specialist from a single breeding programme? Gabriel Rovere Thesis committee Promotor Prof. Dr J.A.M. van Arendonk Professor of Animal Breeding and Genomics Centre Wageningen University, The Netherlands Main Supervisor Aarhus University Dr P. Madsen Senior Researcher, Center for Quantitative Genetics and Genomics Aarhus University, Tjele, Denmark Co-promotors Dr B.J. Ducro Assistant Professor, Animal Breeding and Genomics Centre Wageningen University, The Netherlands Dr E. Norberg Senior Researcher, Center for Quantitative Genetics and Genomics Aarhus University, Tjele, Denmark Other members (assessment committee) Prof. Dr J. Jensen, Aarhus University, Denmark Prof. Dr J.L. van Leeuwen, Wageningen University, The Netherlands Prof. Dr A. Barneveld, Utrecht University, The Netherlands Dr S. Janssens, Katholieke Universiteit Leuven, Belgium This research was conducted under the joint auspices of the Graduate School of Wageningen Institute of Animal Sciences (WIAS), Wageningen University and Graduate School of Science and Technology (GSST), Aarhus University and is part of the Erasmus Joint Doctorate Program “EGS-ABG”. Sport horses: breeding specialist from a single breeding programme? Gabriel Rovere Thesis submitted in fulfillment of the requirements for the joint degree of doctor between Aarhus University by the authority of the Head of Graduate School of Science and Technology and Wageningen University by the authority of the Rector Magnificus, Prof. DrA.P.J.Mol, in the presence of the Thesis Committee appointed by the Academic Board at Wageningen University and the Head of The Graduate School of Science and Technology at Aarhus University to be defended in public on Friday February 12, 2016 at 11 a.m. in the Aula, Wageningen University Rovere, G. Sport horses: breeding specialist from a single breeding programme? 152 pages. Joint PhD thesis, Aarhus University, Aarhus, Denmark and Wageningen University, The Netherlands (2016) With references, with summaries in English, Danish and Dutch ISBN 978-94-6257- 635-3 Abstract The general goal of this thesis was to provide information useful for the breeding programme of the Royal Dutch Warmblood Studbook (KWPN) in relation with the ongoing specialisation of the population. Data provided by KWPN consisted of records from studbook-first inspection, competition performance on dressage and show-jumping, and pedigree information. Firstly, the effect of specialisation was studied on the connectedness between the subpopulations of dressage and show- jumping horses, using the pedigree information. Results indicated that relatedness between horses in the two subpopulations has been reduced to a low level, while relatedness within both subpopulations has been increasing consistently. A reduction in the number of influential ancestors in both subpopulations was observed. Secondly, it was analysed whether the specialisation for either dressage or show jumping has affected genetic parameters of traits recorded in the two subpopulations. Traits recorded at studbook-entry inspection were defined as a dressage trait or a show-jumping trait according to the type of horse that received the inspection. Bivariate analyses were performed to estimate the genetic correlation between the two traits. Results indicated that the specialisation process has resulted in a difference in mean trait values between dressage and show- jumping horses. However, differences in heritabilities for traits defined as dressage or show-jumping did not differ significantly, and the genetic correlations between them were not different from one considering their posterior standard deviation. Thirdly, the model to analyse performance in competition of dressage and show- jumping was studied. Results showed that performance in competition for dressage and show-jumping is a heritable trait (h2 ~ 0.11-0.13), and that it is important to account for the effect of rider in the genetic analysis. Fourthly, it was estimated the genetic correlation between the performance of horses in dressage and show- jumping competition, and the genetic correlations between traits measured early in life and performance in competition in each of the disciplines. Results showed that the genetic correlation between performance of horses in dressage and show- jumping was slightly unfavourable (-0.12). The genetic correlation between dressage and show-jumping tended to become more unfavourable over time, but this trend was not reflected in changes in the correlations between competition traits and traits recorded in the studbook-entry inspection. From this study it can be concluded that no extra benefit is to be expected from definition of a combined breeding goal. However, entirely separated breeding programmes for both disciplines are therefore not advisable. Constructing separate selection indexes would allow for optimal weighting of information sources such as studbook-entry inspection traits in accordance to the breeding goal of each sports discipline. Contents Chapter 1 General Introduction 9 Chapter 2 Genetic connections between dressage and show- 19 jumping horses in Dutch Warmblood horses Chapter 3 Effect of specialisation on genetic parameters of 41 studbook–entry inspection in Dutch Warmblood horses Chapter 4 Analysis of competition performance in dressage and 57 show-jumping of Dutch Warmblood horses Chapter 5 Genetic correlations between dressage, show-jumping 77 and studbook-entry inspection traits in a process of specialisation in Dutch Warmblood horses Chapter 6 General Discussion 97 Summary 121 Sammendrag (in Danish) 127 Samenvatting (in Dutch) 131 List of publications 135 Training and education 141 Acknowledgments 145 Colophon 149 1 General Introduction 1. General Introduction Introduction Horses and equestrian sports are part of the common heritage of Europe. With an increasing number of horse riders and more than six million horses, the equestrian sector has a significant social and economic impact in many European countries (The European Horse Network 2013). With the increasing mechanisation during the second half of the twentieth century, the role of the horses in the society shifted from the traditional activities related to warfare, agriculture and transport to sport and leisure related activities. The horse populations that became popular to fulfil the new needs were the Warmblood breeds. Warmbloods originated in Europe from older local breeds used in agriculture and cavalry. They were derived from breeding between hotblood horses (Thoroughbreds and Arabs) and coldblood horses (draft horses). The different breeds are defined by the studbooks, that have unique and varied histories, and most were established from breeding between local mares and either imported warmblood sires from other breeds or Thoroughbred sires (Hamann and Distl 2008). Warmblood breeds are an open breeding population due to the contribution of different specific breeds (e.g. Thoroughbred, Trakehner) and the genetic exchange among Warmblood studbooks. This genetic exchange between studbooks has increased over the last decades due to more importation of sires or semen, facilitated by the availability and uptake of artificial insemination (Thorén Hellsten et al. 2008; Ruhlmann et al. 2009). The general goal of the Warmblood breeders is to breed riding horses that mainly are used as sport horses. Warmblood horses are popular in the Olympics disciplines, i.e. dressage, show-jumping and eventing. In any case, studbooks have different emphases in their breeding goals. Some of them focus on one sport discipline (e.g. the Irish Sport Horse and Holstein studbooks focus on show jumping, Trakehner focus on dressage), but the majority of the breeder organisations aim to breed horses to compete at professional levels in dressage and show-jumping (Koenen et al. 2004; Stock et al. 2015). However, contrary to other livestock species, there is no precise determination of the weight of different traits in the breeding goal (Koenen et al. 2004). 11 1. General Introduction The breeding goal of the Royal Dutch Warmblood Studbook (KWPN) is focused on performance at the highest level in dressage and show-jumping (KWPN 2015). In the breeding programme, the studbook focuses mainly on selection of stallions while the selection decisions on mares are mostly taken by the breeders. KWPN follows a multistage selection process to select the stallions. The first stage is the entry inspection where the stallions are assessed on conformation, movement and free jumping. The best horses from studbook inspections are selected to participate in the stallion performance test. The horses which approve the performance test are available for breeding. The breeding stallions are finally selected when records from their progeny are available (Ducro 2011; KWPN 2015). Including young horse information into the selection programme is justified because of the favourable genetic correlations between traits recorded in the young horse performance tests and performance in competition (Thorén Hellsten et al. 2006). Specifically for the KWPN population, Huizinga et al.(1991), Koenen et al.(1995) and Ducro et al.(2007) showed that some traits recorded at the young horse inspections were genetically and phenotypically correlated with performance in competition. Therefore, selecting based on inspection traits gives the highest response to selection (Ducro 2011). This has made selection easier, although the weight of the most important traits in breeding goals is not always clear. Historically,