Aus dem Institut für Tierzucht und Tierhaltung der Christian-Albrechts-Universität zu Kiel Reproduction and health in Holstein Warmblood mares - Impact of population structure and data recording – Dissertation zur Erlangung des Doktorgrades der Agrar- und Ernährungswissenschaftlichen Fakultät der Christian-Albrechts-Universität zu Kiel vorgelegt von M.Sc. agr. Lukas Philipp Roos aus Speyer, Rheinland-Pfalz Dekan: Prof. Dr. E. Hartung 1. Berichterstatter: Prof. Dr. J. Krieter 2. Berichterstatter: Prof. Dr. G. Thaller Tag der mündlichen Prüfung: 12. November 2014 Die Dissertation wurde mit dankenswerter finanzieller Unterstützung der H. Wilhelm Schaumann Stiftung, Hamburg angefertigt MEINEN ELTERN TABLE OF CONTENTS GENERAL INTRODUCTION ………………………………………………….. 1 CHAPTER ONE Inbreeding depression in horses: A review ……………………………...….. 5 CHAPTER TWO Investigations into genetic variability in Holstein horse breed using pedigree data ….………………………………………………………… 27 CHAPTER THREE Effect of inbreeding on female fertility in Holstein horse breed …..……….. 50 CHAPTER FOUR Standardisierte Erfassung von Gesundheitsdaten beim Holsteiner Pferd …….………………………………………………………….. 72 GENERAL DISCUSSION …………………………………………………….. 96 GENERAL SUMMARY …….………………………………………………….. 104 ZUSAMMENFASSUNG …………………………………………………..….. 107 GENERAL INTRODUCTION Reproductive performance and health are important key factors in equine breeding and business (Dohms, 2002; Zent, 2003; Sairanen et al., 2009). Equine fertility is known as a tangled functional trait with lots of influencing environmental and management factors such as the age of the animal, the individual servicing at farm level or the season. Thus, it is difficult to determine the fundamental factors directly linked to the individuals (Mucha et al., 2012; Sairanen et al., 2009). Compared to other livestock species, horses generally have lower fertility and are characterised by a large generation interval (Mucha et al., 2012). Several risk factors such as various kinds of fertility disorders could further complicate breeding activities. Not only in horses inbreeding is known as a genetic factor that is capable of affecting fertility, depending on its severity (Charlesworth and Charlesworth, 1987;Charlesworth and Willis, 2009;Falconer and Mackay, 1996). Highly selected and mostly line-bred populations with closed studbooks such as the Holstein horse breed are more likely to produce closely related animals. Increased inbreeding together with decreased effective population size maximise the risk of negative effects on functional traits with low heritability (e.g. health and fertility) (Nomura et al., 2001; Sierszchulski et al., 2005). Besides high-quality pedigree information, consistently recorded phenotypes are essential to estimate any kind of genetic and non-genetic effect on functional traits or to establish new breeding strategies such as genomic selection. Standardised and comprehensive data recording with a centrally managed database for health phenotypes is currently not practiced in German horse breeding. A consistent key system to manage, standardise and to analyse veterinary data is missing. Thus, there is a lack of epidemiological knowledge needed to provide reasonable 1 emphases for selection with regard to health aspects (Sarnowski, 2013). The implication of equine health into breeding schemes, focused on the estimation of breeding values and the implementation of genomic selection, is currently limited by using indirect traits such as conformation and performance (Koenen et al., 2004). In Chapter One of this thesis, a review is presented of the current knowledge of the occurrence and the estimation of inbreeding depression in horses. The objective was to represent a general overview of the extent to which different kinds of traits (fertility, morphology, pathological findings and performance) are affected by the population structure of several horse breeds. Against the background of traditional breeding policies with closed studbooks and restricted licensing of foreign stallions, Chapter Two especially deals with the population structure of Holstein Warmblood horses. The aim was to point out updated levels of inbreeding, the proportions of foreign blood and to specify the genetic contributions of outstanding founders to the current structure of the breeding stock. Additionally, some alternative concepts regarding the evolution of inbreeding were applied. According to the fact that increased inbreeding is able to affect fitness- associated traits in a negative way, Chapter Three investigated the possible impacts of inbreeding and other relevant factors (age effect) on fertility (foaling rate) and the occurrence of fertility disorders (stillbirth) in Holstein Warmblood horses. Building on this, any kind of research into genetic or non-genetic impacts on functional traits necessarily depends on standardised and consistent phenotypic data. Inconsistent phenotypes potentially skewed statistical analysis. Therefore, the aim of Chapter Four was the initial development of a standardised monitoring system for centralised equine health and fertility data recording. An attempt was made to acquire clinical data, using a sample of selected breeding facilities in Schleswig–Holstein, together 2 with their caring veterinarians. The final aspect of this study was the development of a consistent key system to categorise and standardise veterinary field data. References Charlesworth, D., and B. Charlesworth. 1987. Inbreeding Depression and its Evolutionary Consequences. Annu. Rev. Ecol. Syst. 18(1):237–268. doi:10.1146/annurev.es.18.110187.001321. Charlesworth, D., and J. H. Willis. 2009. The genetics of inbreeding depression. Nat Rev Genet 10(11):783–796. doi:10.1038/nrg2664. Dohms, T. 2002. Einfluss von genetischen und umweltbedingten Faktoren auf die Fruchtbarkeit von Stuten und Hengsten. Wissenschaftliche Publikation // Deutsche Reiterliche Vereinigung 25. FN-Verl. der Dt. Reiterlichen Vereinigung, Warendorf. Falconer, D. S., and Mackay, Trudy F. C. 1996.Introduction to quantitative genetics.4th ed. Longman, Essex, England. Koenen, E., L. Aldridge, and J. Philipsson. 2004. An overview of breeding objectives for warmblood sport horses. Livestock Production Science 88(1-2):77–84. doi:10.1016/j.livprodsci.2003.10.011. Mucha, S., A. Wolc, and T. Szwaczkowski. 2012. Bayesian and REML analysis of twinning and fertility in Thoroughbred horses. Livestock Science 144(1):82–88. Nomura, T., T. Honda, and F. Mukai. 2001. Inbreeding and effective population size of Japanese Black cattle. J. Anim. Sci. 79(2):366–370. Sairanen, J., K. Nivola, T. Katila, A.-M.Virtala, and M. Ojala. 2009. Effects of inbreeding and other genetic components on equine fertility. Animal 3(12):1662. doi:10.1017/S1751731109990553. 3 Sarnowski, S., Stock, K. F., Kalm, E.,Reents, R. 2013. Aufbau einer Gesundheitsdatenbank für Pferde. 7. Pferde-Workshop Uelzen, 17th and 18th of september 2014:108–117. Sierszchulski, J., M. Helak, A. Wolc, T. Szwaczkowski, and W. Schlote. 2005. Inbreeding rate and its effect on three body conformation traits in Arab mares. Animal Science Papers and Reports 23(1):51–59. Zent, W. 2003. Foal Heat-Breeding. In: Current Therapy in Equine Medicine. Elsevier. p. 248–250. 4 CHAPTER ONE Inbreeding depression in horses: A review L. Roos and J. Krieter Institute of Animal Breeding and Husbandry, Christian-Albrechts-University, Kiel, Germany 5 Abstract In livestock production, the phenomenon of inbreeding depression is known as the decreasing mean phenotypic performance in related individual’s progeny and is caused by a reduction in homozygosity. This special kind of genetic change is more likely to occur in traits related to fertility and fitness. For other livestock species, it is considered proven that morphological traits are less sensitive to inbreeding depression because of weakly pronounced dominant gene effects. In commercial horse breeding facilities, depressed fitness-related traits or the increased volume of fertility disorders as well as unfavourable morphological development could lead to considerable economic loss. Against this background, the objective of this review article was to give an overview of today’s knowledge of the occurrence and estimation of the extent of inbreeding depression in various horse breeding traits (fertility, morphology, pathological findings and racing performance). Inconsistent findings indicate that, also in horses, fitness-associated traits such as reproductive performance and fertility disorders as well as morphological traits are affected by inbreeding depression. Depending on the structure, quality and depth of the pedigree information, fluctuations were observed in the extent of inbreeding and its impact on the traits analysed when compared in different studies. 6 Introduction Deleterious effects of inbreeding have long been recognised in domesticated species (Darwin, 1868). Inbreeding depression is widely known as the reduction of mean phenotypic performance in related individual’s progeny (Charlesworth and Charlesworth, 1987; Charlesworth and Willis, 2009; Falconer and Mackay, 1996). It is more likely to occur in traits related to reproduction and fitness (Charlesworth and Charlesworth, 1987; Falconer and Mackay, 1996; Hansson and Westerberg, 2002). Morphological traits are less sensitive to this kind of genetic change because of weakly pronounced dominant gene effects (Falconer and Mackay, 1996; Fioretti et al., 2002; Van Eldik et al., 2006; Van Wyk et al., 2009). Generally, inbreeding depression