University of Veterinary Medicine Hannover Genetic ... · introducing new movement traits for more...

University of Veterinary Medicine Hannover

Genetic analyses of movement

traits in German warmblood horses

Thesis

Submitted in partial fulfilment of the requirements for the degree

-Doctor of Veterinary Medicine-

Doctor medicinae veterinariae

(Dr. med. vet.)

by

Ann-Christin Becker

Wilhelmshaven

Hannover 2011

Academic supervision: Prof. Dr. Dr. habil. Ottmar Distl

Institut für Tierzucht und Vererbungsforschung

Bünteweg 17p

30559 Hannover

1. Referee: Prof. Dr. Dr. habil. Ottmar Distl

2. Referee: Prof. Dr. Wilfried Brade

Day of the oral examination: November 17th , 2011

To my father

Parts of this thesis have been accepted or submitted for publication in the following journals:

1. Livestock Science 2. Journal of Animal Breeding and Genetics 3. Animal

Table of contents

1 Introduction……………………………………………………………………………...11

2 Review: Movement disorders and impaired coordinat ion in the horse………………………………………………………………………………………...15

3 Genetic correlations between free movement and mo vement under rider in performance tests of German warmblood horses………………… ……………….39

4 Genetic analyses of new movement traits using det ailed evaluations of

warmblood foals and mares…………………………………………………………….45

5 Correlations of unfavorable movement characterist ics in warmblood foals

and mares with routinely assessed conformation and performance

traits…………………………………………………………………………………………51

6 General discussion…………………………………….……………………….……...5 5

7 Summary…………………..…………………………………………………………..…65

8 Zusammenfassung……………………………………………………………………..71

9 List of publications……………………………………………………………………..7 9

10 Acknowledgement……………………………………………………..……………...83

Chapter 1

Chapter 1 (Introduction)

11

1 Introduction

Modern warmblood breeding aims at producing riding horses which are highly

competitive in sport. Movement and its improvement are therefore in the focus of the

breeding programs. Regardless of the discipline of riding sport, from recreational

riding to dressage or show jumping on an international level, correct gaits and

balanced movements belong to the most important basic qualities. Accordingly, gait

quality has considerable impact on the value of a horse, and scoring of movement

traits is an integral part of the evaluation of foals, broodmares and stallions relevantly

influencing breeding and selection decisions.

Particularly dressage horses have been selected for good movements for a long

time, resulting in modern warmblood horses which move with much more expression

and elasticity than their ancestors. However, horses with certain unfavorable

movement characteristics are still seen in the regular breeding events, so the

question arose whether the current evaluation system is sufficient for reducing this

condition. Therefore, in this thesis data provided by the Oldenburg breeding societies

were used to analyze routinely assessed performance traits and the opportunities of

introducing new movement traits for more specific improvement of gaits. Subjective

scores for gaits during free movement and gaits under rider were chosen for the

genetic analyses of the currently used movement traits, and the new movement traits

were defined on the basis of detailed movement evaluation of foals and mares.

Separate analyses of the already defined and the new movement traits were followed

by extensive correlation analyses which also included conformation traits. The aims

of this study were to learn more about the distribution and genetic background of

unfavorable movement characteristics and to give advice how to interpret them in the

context of future breeding for sport performance.

Overview of chapter contents

The content of the thesis is presented in single papers according to § 8 Abs. 3 of the

Rules of Graduation of the University of Veterinary Medicine Hannover.

Because signs considered indicative of impaired balance were most important

among the unfavorable movement characteristics seen in the warmblood horses,

Chapter 1 (Introduction)

12

literature on incoordination conditions was reviewed to get an overview over the

broad spectrum of possible etiopathologies (Chapter 2).

The estimation of genetic parameters for free movement and movement under rider

using scores from mare performance tests of the Oldenburg Warmblood is presented

in Chapter 3.

The use of detailed movement evaluations of foals and mares of the Oldenburg

horse breeding societies for defining and analyzing new movement traits serving as

measures of impaired balance is described in Chapter 4.

Chapter 5 contains the correlation analyses between the new detailed movement

traits and routinely assessed conformation and performance traits from studbook

inspections and mare performance tests.

Chapter 6 comprises the general discussion and conclusions from the results given

in chapters 2-5.

Chapter 7 is the English summary of this thesis, and

Chapter 8 is the comprehensive German summary which takes the overall research

context into consideration.

13

Chapter 2

Chapter 2 (Review on movement disorders in the horse)

15

Review

Movement disorders and impaired coordination in the horse

A.-C. Becker1, K. F. Stock1,2, O. Distl1

1 Institute for Animal Breeding and Genetics, University of Veterinary Medicine Hannover (Foundation), Buenteweg 17p, D-30559 Hannover, Germany

2 Vereinigte Informationssysteme Tierhaltung w.V., Heideweg 1, D-27283 Verden, Germany


16

Summary

Deviations from balanced and coordinated movement occur in horses as in many

other species, with considerable variation in the severity of clinical signs. Although

the term ataxia does not imply severe clinical manifestation, it is mainly used for the

clearly affected horses. In the riding horse, even slight movement disorders may

interfere with maximum performance capacity, giving reason to review the current

knowledge on equine incoordination in general. After a brief overview over the

disease terminology, etiological factors are mentioned with their presumed relevance

and mode of action. According to literature, the age at which indications of imbalance

are seen may be suggestive of the underlying pathologies, with developmental

orthopedic disease (DOD) being probably responsible for most cases of

incoordination in the young horse. In the adult horse, osteoarthrosis has been

identified as a relevant causative factor. Familial disposition of equine incoordination

has been long discussed, but knowledge on the role of genetics is still sparse.

Clinically, movement disorders of different etiology are usually indistinguishable,

interfering with specific trait definition for genetic analyses. Implications for future

studies on movement disorders and impaired coordination in young and adult horses

are described.

Keywords: Equine incoordination; Spinal ataxia; Gait disturbances; Genetic studies


17

Introduction

Movement disorders and signs of incoordination are unspecific symptoms which

are seen in many species. They occur in the course of various disorders, and there is

considerable variation in severity and duration of the clinical signs. The noticeable

problems range from very slight and intermittent deviation from normal motion

sequence to distinct lack of coordination. Because of the often slight and unspecific

clinical signs, it was surmised that the role of diseases interfering with balanced

movement in the horse may have been underestimated (Van Biervliet, 2007).

Central nervous structures are responsible for the regulation of all motor activity,

with cerebellum and spinal cord being most important. Accordingly, distinction can be

drawn between cerebellar ataxia and spinal ataxia. The highly complex function of

the nervous system with its connections to all parts of the body implies vulnerability.

Trauma of the spinal cord was mentioned as possible cause of gait disturbances as

early as in 1861 (Youatt, 1861, cited by Fraser and Palmer, 1967). In the 20th

century, affections of the spinal cord were studied more closely, and changes of the

cervical vertebrae were identified as possible primary lesions (Dimock and Errington,

1939). Research mainly addressed etiological factors affecting stability and function

of the cervical vertebral column on the one hand and therapeutic approaches on the

other hand. However, the diverse etiology of movement disorders and incoordination

interfered with the development of general therapeutic concepts. Furthermore,

reversibility of impaired nerval function may be questionable, so that the importance

of prophylactic measures increases. Because affection rates of impaired coordination

were reported to differ considerably between families, relevant involvement of genes


18

was surmised. This review will give an overview about the current knowledge on

movement disorders and incoordination in the horse, referring to the hereditary

aspects of primary diseases.

Terminology

In the literature, different terms can be found for disorders coming along with

disturbed motion pattern. Nomenclature is either symptomatic (descriptive) or

etiological (specific). The descriptive term 'Wobbles', which was later changed to

'Wobbler syndrome', was introduced as summary phrase for the set of clinical signs

observed in incoordinated horses suffering from spinal ataxia (Dimock and Errington,

1939). Wobblers may be affected by infectious or non-infectious diseases, but share

the inability to move in balance.

Subsequently, the Wobbler syndrome was addressed in several studies which

basically confirmed the initial findings (Rooney, 1962; Pohlenz and Schulz, 1966;

Mechlenburg, 1967; Dahme and Schebitz, 1970; Mayhew, 1978). Refinement of

diagnostics later allowed identifying compression of the spinal cord, primarily in the

cervical part, as the most frequent cause of incoordination in the horse. Within the

context of developmental orthopedic diseases (DOD), cervical vertebral malformation

(CVM) was described in the 1990s (Stewart et al., 1991). To highlight the clinically

relevant affection of the nerval structures, the disease was referred to as cervical

stenotic myelopathie (CSM; Moore et al., 1994). Variation in clinical manifestation

was accounted for by distinction between constant or static stenosis (cervical static

stenosis, CSS) and recurrent or dynamic stenosis (cervical dynamic stenosis, CDS;

Moore et al. 1994).


19

However, deformations of cervical vertebrae may also represent secondary

changes, and their occurrence is not confined to the young and growing horse (Van

Biervliet, 2007). With diagnostic focus on the cervical vertebral spine it may not be

possible to identify the underlying disease, implying reference to symptomatic

nomenclature.

The general term ataxia which resembles a symptom rather than a disease

basically stands for any deviation from coordinated and balanced movement.

However, it is uncommon to use this term in cases with only subtle indications of

impaired coordination. Accordingly, horses with have been diagnosed as atactic

usually show rather obvious clinical signs.

Etiology

Given the heterogeneity of impaired coordination in the horse, over the years a

large variety of etiological factors has been discussed. Current knowledge about the

most important factors will be summarized in the following.

Nutrition and growth

As the skeletal and nerval development is dependent on the appropriate supply

with several nutrients, dietary aspects were early suggested as important factors in

the whole DOD complex.

The coincidence of overfeeding and DOD has often been reported and discussed

(Hoppe, 1984; Jeffcott, 1991). However, differences may exist between the diseases

belonging to the DOD complex. For osteochondrosis, some authors surmised a

general association between body weight and the proportion of horses affected with


20

osteochondrosis dissecans (Pagan and Jackson, 1996). Others found differences

between joints with effects of body weight being possibly more relevant for the hock

joints than for the fetlock joints (Wilke, 2003). Among the horses presented with

noticeably impaired coordination there was an overrepresentation of big and fast

grown individuals (Mayhew, 1978; Nixon, 1982; Mayhew, 1989).

Overfeeding of the growing horse with energy and protein may exert detrimental

effects in different ways. Fast gain of weight and above-average body weight at a

young age increase the stress exerted on the maturating skeleton. Maturation

processes may be disturbed by the high loading, and imbalance between strength of

the skeleton and weight to be carried may persist (Thompson, 1987). Effects of

inappropriate diet composition may be intensified in situations where growth is

maximized through excessive energy supply. Even slight absolute or relative

deficiencies of nutrients may then become clinically relevant.

In connection with skeletal development, calcium and phosphorus are long known

to be important. Deficiencies, excesses and inappropriate ratios of these two

minerals can lead to persistent weakness of bones and joints (Savage et al., 1993).

Copper is essential for the development of cartilage and nerve tissue, implying

possible relevance for equine incoordination. Neurological symptoms have early

been compared between sheep and horse (Olafson, 1942), and possible

responsibility of copper in both species has been discussed. However, conflicting

results were obtained with regard to effects of copper on cartilage and bone in foals

(Knight et al., 1985; Knight et al., 1990; Hurtig et al., 1990; Davies, 1998; Pearce,

1998; Coenen et al., 2003; Vervuert et al., 2003). Surmised influences of vitamin A,

possibly in combination with an inappropriate calcium to phosphorus ratio, on the


21

development of impaired coordination could not been verified in early studies

(Bardwell, 1961). A lack of vitamin E is a possible cause of neurological symptoms

across species and age groups. In the adult horse hypovitaminosis E was made

responsible for degenerations of motor neurons in the spinal cord (McGorum and

Mayhew, 2006; Mohammed, 2007). Horses affected by equine degenerative

myeloencephalopathy (EDM) first show signs of incoordination and clumsiness,

which deteriorates to outright ataxia (Kane, 2009).

Age and use

CVM has long been considered as a disease of the young horse (Levine et al.,

2010). However, several studies addressing the influence of age on the prevalence

of CVM did not support this assumption. The results indicated that the pathogenesis

of CVM may be different in young and adult horses, but incoordination because of

malformation of cervical vertebrae may also develop in older age (Levine et al.,

2010). In the young horse, the majority of cases may be caused by DOD, whereas in

the adult horse the importance of degenerative changes increases (Van Biervliet,

2007). Osteoarthritic enlargement of articular processes may be clinically inapparent

in many horses, but responsible for clearly impaired coordination in others (Levine et

al., 2010).

The use of horses was suggested to have an effect on CVM development in the

adult horse. Prolonged cervical stress in intensively used riding horses may be

interpreted as repeated vertebral microtrauma. Sport horses may therefore be on a

higher risk to develop CVM than horses used for pleasure riding or breeding. In a


22

recent study which included 270 horses with signs of incoordination no significant

differences were found between different types of use (Levine et al., 2010).

Trauma

Any trauma exerted on the nerval structures involved in regulation of motor activity

can lead to movement disorders. Accidents with fractures or luxations of single or

multiple vertebrae are likely to affect motor neurons in the spinal cord. However, in

many cases it may be difficult to state on the primary cause of incoordination. Slight

signs of imbalance may have been present, but not recognized before the accident.

Horses with coordination problems are stumbling more frequently and have a higher

risk of falling. Accidents of such horses which lead to obvious clinical signs are

consequences rather than causes of movement disorders.

Hematomas extending into the vertebral canal can cause clinical signs resembling

those of vertebral fractures or luxations. However, with resolution of the hematoma

functional recovery will set in rather quickly.

Disturbed blood supply

Vascular occlusion may not only secondary to for example traumatic compression

of the spinal cord, but also occur primarily. Local cut-off or significant reduction of

blood supply will result in asymmetric gait deficits or incoordination. Typical clinical

signs for ischemic myelopathy are intermittent limping or incoordinated movement of

limbs. In many cases, the neurological signs are transitional, and the ischemic

lesions may heal after revascularization (Al-Mefty et al., 1993).

Infectious diseases


23

Because of the complex interconnections of nerval structures, any infection

affecting the nervous system can result in movement or coordination disorders.

Equine Herpes Virus (EHV) is well known as a cause of respiratory diseases or

aborts. However, EHV-1 and less often EHV-4 may also evoke myeloencephalitis in

horses of different ages, even in vaccinated ones (Blunden, 1992). The clinical signs

vary widely, depending on which section of the spinal cord, the brain or the nerves

have been affected. In the majority of cases an early sign of EHV myeloencephalitis

is ataxia of the hind limbs. To clinically differentiate ataxia caused by EHV infection

from CVM, case histories are to be considered. Horses that have been infected by a

Herpesvirus usually show high fever and respiratory symptoms ten to fourteen days

before they develop ataxia. Furthermore, the neurological symptoms of central

nervous EHV may quickly improve, often within two to four days, whereas CVM

related symptoms remain stationary or deteriorate.

Other virus infections which may involve impaired coordination in the horse include

the neurotropic Rabies virus and the West Nile Virus. Western and Eastern Equine

Encephalitis or Myeloencephalitis are caused by infections with closely related RNA

viruses. Both have been primarily diagnosed in the USA and in Canada, but with

international equine trading and traveling the risk of outbreaks in northern Europe

may increase. Manifest infection with West Nile Virus may cause neurological

symptoms in horses such as staggering or incoordinated gaits (Nielsen et al., 2008).

However, infections are frequently asymptomatic, with an apparent-to-inapparent

ratio of as high as 1:17 in 2005 (Nielsen et al., 2008).


24

Infection with Borrelia burgdorferi may cause clinically apparent Lyme disease in

horses. A broad spectrum of possible manifestations has been discussed rather

controversially, including impaired coordination (Schönert et al., 2008).

Equine protozoal myeloencephalitis is caused by species of Sarcocystis or

Toxoplasmosis in the brain and/or spinal cord. Clinical signs vary depending on the

location and extent of lesions, but ataxia is frequently seen in infected horses (Clark

et al. 1981). A very similar clinical picture may be observed in horses with nematode

infection of the central nervous system, a disease called nematodiasis (Pohlenz,

1965).

Neoplastic changes

Neoplasm can occur in almost every part of the organism, including those with

regulatory elements of motor function. Neoplasias of the nerve tissue itself directly

interfere with regular nerve function and may cause movement disorders. In addition,

neoplasias of tissues surrounding nerval structures can lead to neurological

symptoms through compression effects. The central nervous system is protected by

firm bone, implying rigid space limitation. Accordingly, any tumor growth within the

bony compartments is likely to cause functionally relevant compression of nerve

structures. Because of its quantitative importance, one type of neoplasias will be

mentioned explicitly.

Melanomas frequently develop in grey horses, with the root of the tail representing

one of the main locations. The risk of melanomas generally increases with age, but

the number or size of externally visible tumors does not always reflect the total

burden. Melanomas will lead to ataxic signs as soon as they emerge in the vertebral


25

canal and compress the spinal cord (Schott et al., 1990). Acute and progressive

neurological dysfunction may then be observed even in absence of any cutaneous

melanomas (Traver et al., 1977).

Hormonal balance

Endocrine factors influence the development and maturation of cartilage and bone

(Glade, 1986). DOD is characterized by a disturbance of the conversion of cartilage

to compact bone, so imbalances of hormones involved in cartilage and bone

metabolism are among the possible causes of DOD. Thyroid hormones T3 and T4

exert their influence on skeletal development through their effects on blood supply

(Glade et al., 1984), whereas the growth hormone directly stimulates the activity and

proliferation of chondrocytes (Savage et al., 1993). Parathyroid hormone and

calcitonin are antagonists which together with vitamin D control the blood calcium

and phosphorus concentrations. Imbalances in these minerals interfere with regular

osteoblastic and osteoclastic activity, and the effects of disturbed bone metabolism

may include movement disorders.

In many studies signs of CVM were more often seen in male than in female horses

(Reed et al., 1985; Van Biervliet, 2007; Levine et al., 2007). Although the definite

reason for these sex differences is still unknown, sexual hormones may be directly or

indirectly involved. Estrogen and testosteron both influence bone metabolism, and for

humans it has been described that the shape of vertebrae differs significantly

between the genders (Grados et al., 1999). Sex-dependent behavior patterns have

been described for the horse (Levine et al., 2007). Accordingly, rougher play of colts

when compared to fillies may put them on a higher risk of spinal injuries.


26

Furthermore, recovery after affections of nerval structures may be better in females

than in males according to their progesterone levels. For the rat is has been shown

that progesterone increased the expression of neuroprotective factors and

progesterone treatment improved the outcome after acute spinal cord injuries

(Thomas et al., 1999; Labombarda et al., 2010).

Intoxication

Substances with neurotoxic potential may be responsible for impaired coordination

in single horses or groups of horses. For example, acute selenium poisoning can

lead to amyosthenia with the clinical picture of ataxia (Step et al., 1991). The plant

horse-tail (Equisetum spp.) contains an antagonist of vitamin A absorption.

Intoxication symptoms therefore resemble those of hypovitaminosis A with

degenerative structural changes in the brain and spinal cord and consecutively

disturbed motor activity.

Clinical signs

Clinical signs of incoordination vary wide from slightly imbalanced movement or

irregular tension and rigidity in the hind limbs over weakness and reluctance to carry

weight to clearly atactic movement, spasticity or even paresis (Van Biervliet, 2007).

After for example accidents or infections, severe symptoms of ataxia may become

visible quickly. However, in many cases the clinical picture develops slowly, with first

signs of imbalance being barely apparent and presumably often unrecognized. Table

1 gives an overview over the symptoms mentioned in literature which are considered

to be indicative of incoordination in the horse.


27

Clinical signs alone do not allow etiological diagnoses. Use of refined diagnostics

has shown that lesions of the cervical spinal cord lesions may be the most important

causes of impaired coordination in the horses. Clinically obvious irregularities of gaits

are in such cases primarily related to either dysfunction of the upper motor neuron

(UMN) or general proprioceptive (GP) tracts. However, close connections and

functional dependencies of UMN and GP cause symptoms resulting from both UMN

and GP dysfunction. Generally, extent and severity of movement disorders depends

on the location of neural lesions. Therefore, in some cases all four limbs can be

affected, which appears rarely and mainly in severe cases, or only the hind or front

limbs. Gait deficits are often symmetric, but may also be asymmetric. Asymmetry of

movement disorders is not indicative of any specific etiology and is independent of

age (Levine et al., 2010). In many cases, first clinical signs of impaired coordination

are seen in the hind limbs which is due to the superficial location and accordingly

higher trauma exposure of respective motorneurons in the spinal cord.

Heritability and mode of inheritance

Genetic disposition of equine incoordination has been considered since the very

beginning (Dimock and Errington, 1939; Dimock, 1950). In 1950, Dimock interpreted

his study results as proofs for the hereditary nature of the Wobbler disease and

suggested a recessive inheritance. This suggestion was in agreement with previous

literature (Weischer 1944), but was questioned subsequently (Jones et al., 1954).

Decades later, the question of heredity of DOD was addressed by a breeding

experiment (Wagner et al., 1985). The results justified using the summary term DOD

for Wobbler disease and osteochondrosis, but did not allow clear conclusions


28

regarding the former: Mating of two Wobblers did not increase the proportion of

wobblers among their offspring. However, their risk of developing osteochondrosis

was significantly elevated (Wagner et al., 1985).

Differences between breeds regarding the dispositions of movement disorders have

been long discussed and may indicate relevant genetic influences. Several

investigators found Thoroughbreds to be overrepresented among the horses with

incoordinated movement (Falco et al., 1976; Mayhew et al., 1978). However, when

interpreting information on affection rates per breed, the sources of information must

be taken into account. Most studies on equine incoordination are based on case

material of certain clinics, and it cannot be assumed that breed representation is

representative. When a large equine hospital is located in a region where for example

Thoroughbred breeding is very common, it may be expected that Thoroughbreds will

also make up the largest part of incoordination cases (Gordis, 2004).

Until today conclusive information on the role genetics for incoordination in the

horse is missing. The heterogeneous etiology of movement disorders makes trait

definition difficult, and the information on the prevalences of the primary diseases is

still very sparse. Most literature refers to clinical data unsuitable for population

genetic analyses. Neurological patients or all patients of an equine hospital do not

represent random samples of the horse population, and determined incidence rates

are likely not to reflect the overall situation. To reliably estimate genetic parameters,

screening data will be the ideal source of phenotype information. However, trait

definition has to be considered thoroughly, keeping the balance between maximum

specificity of information and feasibility of broad data collection.


29

Implications for further studies

It has been postulated that distinction between the causes of spinal cord

compression may be necessary to appropriately interpret collected data on

incoordination (Van Biervliet, 2007). Statements on prognosis and therapeutic

options for the individual horse will require knowledge on the specific etiopathology,

implying the use of refined diagnostics. However, less detailed information may be

used to get an impression of the role and quantitative importance of movement

disorders and incoordination in a horse population. Performing elaborate

examinations like cervical spine radiography, magnetic resonance tomography or

computed tomography in hundreds or thousands of horses in unrealistic, but would

be necessary to distinguish etiologically.

According to the available study results it may be legitimate to assume

predominance of one etiology each in young and adult horses: Incoordination may in

the young horse primarily relate to DOD and in the adult horse to osteoarthrotic

changes. Most of the sporadic causes of incoordination can be excluded by refined

diagnostics, for example toxicological screening of the blood. Clinical appearance

may then be used to assess the disease status with respect to incoordination in

distinct age groups. Simplified data collection should be feasible in large numbers of

horses, resulting in datasets large enough for population genetic analyses. Ideally,

collection of incoordination data could be combined with routine inspections of young

and adult horses. In this connection it must be taken into account that horses with

obvious ataxia are unlikely to be presented at the regular inspection dates and cases

of very slight impairment of coordination may be undetected when only the clearly

indicative signs of ataxia (see Table 1) are considered. The set of clinical signs to be


30

recorded may therefore include additional characteristics of movement pattern.

Because of the importance of neck and tail for balanced movement, documentation

of posture and tension of neck and tail during movement may provide valuable

information. Genetic parameters may then be estimated separately for signs of

imbalance in young and adult horses to account for probably different etiologies and

pre-selection effects in the two age groups.

Conflict of interest statement

None of the authors of this paper has a financial or personal relationship with other

people or organisations that could inappropriately influence or bias the content of the

paper.


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Mechlenburg, G., 1967. Untersuchung der Halswirbelsäule und des Rückenmarks beim Pferd im Hinblick auf Veränderungen bei der spinalen Ataxie. Veterinary medical thesis, University of Veterinary Medicine Hannover, Hanover / Germany.

Mohammed, H.O., 2007. Vitamin E deficiency and risk of equine motor neuron disease. Acta veterinaria Scandinavica 49, 17.

Moore, A., Collatos, C., Ortenburger, A., Illanes, O., Ikede, B., 1994. Motor neuron disease in a horse. Canadian Veterinary Journal 35, 522.

Nielsen, C.F., Reisen, W.K., Armijos, M.V., MacLachlan, N.J., Scott, T.W., 2008. High subclinical west nile virus incidence among nonvaccinated horses in northern california associated with low vector abundance and infection. American Journal of Tropical Medicine and Hygiene 78, 45-52.

Pagan, J.D. and Jackson, S.G. (1996) The incidence of developmental orthopaedic disease on a Kentucky Thoroughbred farm. Pferdeheilkunde 12, 351-354.

Olafson, P., 1942. Wobblers compared with ataxic “swing back lambs”. Cornell Veterinarian 32, 301-314.

Pagan, J., 2005. The role of nutrition in the management of developmental orthopedic disease. Advances in equine nutrition 3, Nottingham University Press, Nottingham / UK, pp. 417-431.

Pearce, S.G., Firth, E.C., Grace, N.D., Fennessy, P.F., 1998. Effect of copper supplementation on the evidence of developmental orthopaedic disease in pasture-fed New Zealand Thoroughbreds. Equine Veterinary Journal 30, 211-218.

Pohlenz, J., Schulze, D., Eckert, J., 1965. Spinale Nematodosis beim Pferd, verursacht durch Strongylus vulgaris. Deutsche Tierärztliche Wochenschrift 72, 510-511.

Pohlenz, J., Schulz, L.-C., 1966. Rückenmarksveränderungen bei der spinalen Ataxie des Pferdes in ihrer Abhängigkeit von Ort und Grad der Veränderungen am Halswirbelskelett. Deutsche Tierärztliche Wochenschrift 73, 533-536.

Reed, S.M., Fenner, W.R., 1985. The approach to spinal cord disease in horses. Proceedings of the American Association of Equine Practicioners 31, 19-26.

Rooney, J., 1963. Equine incoordination. I. Gross morphology. Cornell Veterinarian 53, 411-422.

Ruppanner R., De Gelinas, L., Marcoux, M., 1972. Equine incoordination. Canadian Veterinary Journal 13, 180-183.

Savage, C.J., 1993. Effects of dietary energy and protein on induction of dyschondroplasia in foals. Equine Veterinary Journal Supplements 16, 74-79.


34

Schebitz, H., Schulz, L.C., 1965. Zur Pathogenese der spinalen Ataxie beim Pferd. Deutsche Tierärztliche Wochenschrift 72, 496-501.

Schönert, S., Gall, Y., Grabner, A., 2008. Lyme-Borreliose beim Pferd - vergleichende Diagnostik und Fallbeispiel eines Ponies mit Meningitis. Tierärztliche Praxis Großtiere 36 (Supplemente 1), 49-53.

Schott, H.C., Major, M.D., Grant, B.D., Bayly, W.M., 1990. Melanoma as a cause of spinal cord compression in two horses. Journal of the American Veterinary Medical Association 196, 1820-1822.

Stewart, R.H., 1991. Frequency and severity of osteochondrosis in horses with CSM. American Journal of Veterinary Research 52, 873-879.

Thomas, A.J., Nockels, R.P., Pan, H.Q., Shaffrey, C.I., Chopp, M., 1999. Progesterone is neuroprotective after acute experimental spinal cord trauma in rats. Spine 24, 2134-2138.

Traver, D.S., Moore, J.N., Thornburg, L.P., Johnson, J.H., Coffma, J.R., 1977. Epidural melanoma causing posterior paresis in a horse. Journal of the American Veterinary Medical Association 170, 1400-1403.

Wagner P.C., Grant, B.D., Watrous, B.J., Appell, L.H., Blythe, L.L., 1985. A study of the heritability of cervical vertebral malformation in horses. Proceedings of the American Association of Equine Practitioners 31, 43-50.

Weischer, F., 1944. Erbbedingtheit der sog. Kreuzlähme bei jungen Pferden. Berliner und Münchener tierärztliche Wochenschrift 39, 317-320.


35

Table 1 Clinical symptoms of incoordination (ataxia) in the horse according to

literature.

Clinical symptom Reference

Incoordinated movement of hind limbs Dimock and Errington, 1939; Dimock, 1950; Schebitz and Schulz, 1965; Fraser and Palmer, 1967; Dahme and Schebitz, 1970; De Lahunta et al., 1983; Levine et al., 2010

Weakness and / or reduced propulsive activity of the hind legs

Reed, 1985; Schütte, 2005; Biervliet 2007

Incoordinated movement of front limbs

Dimock, 1950; Biervliet, 2007; Levine et al., 2010

Asymmetric gait deficits Fraser and Palmer, 1967; Biervliet, 2007; Levine et al., 2010

Dysmetria Dahme and Schebitz, 1970; De Lahunta, 1983; Reed, 1985

Cervical hyperesthesia and / or pain response to flexion of the neck

Dimock and Errington, 1939; Fraser and Palmer, 1967; Mayhew et al., 1978; De Lahunta, 1983; Schütte, 2005; Levine et al., 2010

Spasticity Mayhew, 1978; De Lahunta, 1983; Reed, 1985; Biervliet, 2007;

Paresis Mayhew, 1978; Biervliet, 2007

Varying stride length Reed, 1985; Biervliet, 2007

Dragging of the hooves Schebitz and Schulz, 1965; Dahme and Schebitz, 1970; Böhm, 1975; Reed, 1985; Biervliet, 2007

Outward or inward swaying of the lower limbs

Dahme and Schebitz, 1970; Biervliet, 2007

Balance problems when exercised on small circles

Ruppanner, 1972; Reed, 1985; Biervliet, 2007

Affinity to fall Dahme and Schebitz, 1970; Böhm, 1975; Mayhew, 1978; Schütte, 2005

Pace irregularity Böhm, 1975; Reed, 1985

37

Chapter 3

Chapter 3 (Movement evaluations in mare performance tests)

39

Genetic correlations between free movement and movement under rider in

performance tests of German Warmblood horses

A.-C. Becker1, K.F. Stock 1,2, O. Distl 1

1 Institute for Animal Breeding and Genetics, University of Veterinary Medicine

Hannover (Foundation), Buenteweg 17p, D-30559 Hannover, Germany 2 Vereinigte Informationssysteme Tierhaltung w.V., Heideweg 1, D-27283 Verden,

Germany

Livestock Science 142 (2011), 245-252


40


41

Abstract

Performance information on 2758 mares that had completed mare performance tests

(MPT) of the Oldenburg horse breeders' society in 2000–2008 was used for genetic

analyses focusing on options to improve existing breeding programs through refined

trait definition. Testing conditions were largely unchanged in the study period, with

most data referring to MPT results of 3- or 4-year-olds. For all mares, scores on a

scale from 1 to 10 were available for walk, trot, canter, rideability, and free jumping,

with gait scores representing means from evaluation during free movement (F) and

under rider (R). Distinct F and R gait scores were available for a subset of the mares

with MPT in 2003–2008 and were used to investigate the effect of evaluation type on

variance components. Genetic parameters were estimated with residual maximum

likelihood (REML) in multivariate linear animal models. Heritability estimates for the

MPT traits ranged from 0.19 (rideability) to 0.56 (free-jumping). For the gaits

heritabilities were similar (canter) or higher (walk, trot) for F scores than for

corresponding R scores. The correlations between F and R scores for the same gait

were found to be closer additive genetically (rg=0.7–0.9) than phenotypically (rp=0.4-

0.6), but indicated that F and R scores may not represent exchangeable measures of

the same trait. Further correlation analyses revealed moderately to highly positive

additive genetic correlations between gaits and rideability for both F and R scores,

whereas additive genetic correlations between walk and canter and between trot and

free jumping was relevantly dependent on evaluation type. Because selection of

riding horses represents multiple-trait selection, better reflection of covariances

between selection traits will help maximizing the overall breeding progress. According

to our results, Warmblood breeding may therefore benefit from refinement of trait

definition with clear distinction between gait evaluation during free movement and

under rider.


42

43

Chapter 4

Chapter 4 (Genetic analyses of new movement traits)

45

Genetic analyses of new movement traits using detailed evaluations of

warmblood foals and mares

A.-C. Becker1, K. F. Stock1,2, O. Distl1 1Institute for Animal Breeding and Genetics, University of Veterinary Medicine

Hannover, Hanover, Germany 2Vereinigte Informationssysteme Tierhaltung w.V., Verden, Germany

Journal of Animal Breeding and Genetics 129 (2012), 390-401


46


47

Summary

Detailed movement evaluations of warmblood foals and mares were performed in

connection with regular breeding events of the Oldenburg horse breeding societies in

2009 and 2010. Unfavorable movement characteristics considered indicative for

impaired balance were noted by a special judge (SJ) and the regular judges of the

breeding events (RJ) and served as the basis for definition of new movement traits.

Detailed movement information on 3,374 foals and 2,844 mares showed that more

severe findings like irregular motion pattern in hind legs or irregularity in general

motion pattern occurred only sporadically (prevalences of 1-2%). Irregular tail tone or

posture was documented for 4% of the foals and 5% of the mares, resulting in

prevalences of the comprehensive trait indications of imbalance (IMB) of 6.2% (foals)

and 5.5% (mares). Binary coding was used for all traits, and genetic parameters were

estimated bivariately in linear animal models with residual maximum likelihood

(REML). Comparative analyses between judges revealed that differences between

trait definitions of SJ and RJ were larger in the mares than in the foals, but justified

combined use of SJ and RJ information in both age groups. Heritability estimates for

the movement traits ranged on the original scale from 0.02 to 0.26 in the foals and

from 0.03 to 0.12 in the mares, with heritabilities for IMB on the underlying liability

scale of 0.46 (foals) and 0.22 (mares). Comparative analyses between age groups

indicated that common genetic factors may be responsible for findings of impaired

balance in foals and mares. The results implied that horse breeding may benefit from

using the early available information on the movement of foals obtained by detailed

movement evaluations. New movement traits reflecting unfavorable movement

characteristics may be suitable to select against indications of imbalance in juvenile

and adult horses, although favorable combination of foal and mare data in future

genetic evaluations may require refined recording of unfavorable movement

characteristics in the adult horses.

49

Chapter 5

Chapter 5 (Correlation analyses of new movement traits)

51

Correlations of unfavorable movement characteristics in warmblood foals and

mares with routinely assessed conformation and performance traits

A.-C. Becker1, K. F. Stock1,2, O. Distl1

1Institute for Animal Breeding and Genetics, University of Veterinary Medicine

Hannover, Hanover, Germany; 2Vereinigte Informationssysteme Tierhaltung w.V., Verden, Germany

Animal 7 (2013), 11-21

Chapter 5 (Correlation analyses of new movement traits)

52

Summary

New movement traits reflecting unfavorable movement characteristics were defined

on the basis of detailed movement evaluations (DME) of warmblood foals and mares

performed in connection with regular breeding events of the Oldenburg horse

breeding societies in 2009 and 2010. DME information was available for 3,374 foals

and 2,844 mares and used for correlation analyses with conformation information on

1,987 mares from studbook inspections (SBI) in 2009 and performance information

on 2,758 mares from mare performance tests (MPT) in 2000-2008. Analyses of

variance revealed few significant differences between scores for SBI and MPT traits

in mares without and with indications of imbalance (IMB) in general or specific

findings like irregular tail tone or posture (TTP). SBI scores for general impression

and development were significantly lower and MPT scores for trot under rider tended

to be higher in IMB-positive mares. Genetic parameters were estimated in linear

animal models with residual maximum likelihood (REML). Additive genetic

correlations and Pearson correlation coefficients between univariately predicted

breeding values indicated unfavorable genetic correlations of IMB and TTP with

dressage related conformation and performance traits. For SBI and MPT traits we

found similarities between the correlation patterns for DME traits in foals and mares.

The results implied that breeding of dressage horses may benefit from revision of

current movement evaluation and consideration of specific movement characteristics.

53

Chapter 6

Chapter 6 (General discussion)

55

6 General discussion

In this thesis, different aspects of movement and its evaluation in the warmblood

horse were addressed. The breeding aim of modern Warmblood breeding

organizations is a capable and healthy horse, with an appealing conformation as well

as expressive and correct gaits. Because gaits rank high among the breeding

objectives of the warmblood breeding organizations (Koenen et al. 2004), including

the Oldenburg breeding societies, movement evaluations are integral parts of

breeding events. From foal evaluations over conformation evaluations, for example in

connection with studbook inspections, to performance evaluations in field or station

performance tests, walk and trot and sometimes also canter are judged by

experienced representatives of the breeding societies. Starting with rather general

evaluation at very young age in foals specificity of gait scoring increases in the

juvenile and young adult horse. Several studies have shown that young horse

performance tests are indicative for future success in sport (Ducro et al. 2007a,

2007b; Lührs-Behnke et al. 2006a; Thoren Hellsten et al. 2006; Viklund et al. 2010a,

2010b; Wallin et al. 2003), justifying the efforts of breeding organizations to organize

distinct events for early and standardized testing. However, even in these tests the

traditional evaluation systems use broad trait definitions and do not allow any

inferences on certain movement characteristics. Furthermore, subjective scores on a

1-10 scale are used in all evaluation settings, and the insufficient use of the score

scales is a problem that has been frequently discussed (Stock and Distl, 2006; Stock

and Distl, 2007; Viklund et al., 2010). Specific movement characteristics are not

documented systematically and therefore unavailable when selection decisions have

to be made.

Only very few breeding organizations conduct Young Horse Tests for mares or

stallions evaluating and scoring the gaits under two different evaluation conditions,

during free movement (F) and under rider (R). Because of the standardized testing

protocols and documentation of separate scores for the gaits without and with rider

the data of the Mare Performance Test (MPT) conducted by the Oldenburg breeding

societies were considered suitable for this study to analyze the rider's influence and

investigate the correlations between free movement and movement under rider. Gait


56

evaluations without rider often refer to only walk and trot at hand, whereas MPT for

the Oldenburg Warmblood considers all three gaits shown when the mares move

loosely in the arena. F scores are accordingly characterized by the absence of any

direct influence of the handler on the outcome of movement evaluation on the tested

mares. Without question the effort of time is greater scoring horses free moving and

under the rider, but the study results recommend the additional effort.

According to our results gait evaluation during free movement should allow better

distinction between genetically favorable and unfavorable individuals than gait

evaluation under the rider, particularly with regard to trot. Evaluation during free

movement reflects the natural gait quality of the individual horse. Scores for walk, trot

and canter showed clear differences between evaluation types with largest

differences for trot, the gait which is known to be most influenced by the rider. Scores

evaluated free showed less variation than the corresponding scores under rider.

Heritabilities were higher for trot free than under rider, whereas h² for walk (F and R)

and canter (F and R) were almost identical. In this study the F scores and R scores

were closer correlated additive genetically than phenotypically. However, estimates

of rg =0.7-0.9 clearly indicated that corresponding F and R scores do not resemble

exchangeable measures of the same trait. For routine genetic evaluations across

Warmblood breeds this has to be taken into account. Joint analyses of performance

data based on overall gait scores without consideration of the evaluation type would

create the loss of specificity or even bear the risk of biased results. Movements of a

horse are directly influenced by the rider. A skillful rider certainly improves the

movement qualities of a horse compared to a horse ridden by an inexperienced rider.

Favorable movement under rider does not only reflect good abilities, but also a

certain level of trust and cooperativeness. With increasing professionalism of horse

training and riding sport, appropriate interpretation of gait scores may require taking

the influence of the rider into account. This is currently done in the genetic evaluation

for performance in sport, but not for performance test data.

Multivariate analyses revealed that R scores for the gaits were only moderately

and not much closer correlated with rideability than the respective scores.

Accordingly, rideability scores do obviously not reflect the better or worse ability of a


57

horse to move under rider. Because successful dressage horses have to be able to

show their movement potential under rider, scoring of gaits under rider is and will be

an integral part of performance tests. However, free movement may provide

additional information that is relevant for breeding. Correlations between gaits and

jumping depended on whether F scores or R scores were considered, and the same

was surmised to be true for other traits, including certain movement characteristics.

The selection programs for German warmblood horses are currently based on

subjective gait and conformation scores on a scale from 1 to 10, still the most

common method of conformation and performance evaluation. Although slight

differences in the trait definitions may exist between the breeding organizations, the

standard set of traits evaluated has been unchanged in Germany for at least two

decades. To better capture the variability in the population, splitting-up of the

standard traits and descriptive scoring on linear scales have been recommended

repeatedly, but have been introduced by very few horse breeding organizations yet:

1989 in the Royal Warmblood Studbook of the Netherlands (KWPN; Koenen et al.

1995), and 2003 in the studbook of the Belgian warmblood horse (BWP; Rustin et al.

2009). In this study new movement traits were defined on the basis of detailed

movement evaluations (DME) traits, suitable to support rather than replace the

routine evaluations of foals and mares, but nevertheless compatible with linear

scoring.

Gait characteristics have moderate to high heritabilities and made remarkable

breeding progress in the last decades possible (Viklund et al., 2010). However,

improvement of certain gait characteristics indicative of gaits of high quality will

probably require more specific trait definition (like stride length in trot, elasticity in trot)

and replacement of the traditional subjective scale by an objective linear scale of

scores. Although an objective scale should clearly allow more precise evaluation,

benefits of linear scoring will only become visible and usable for selection, when the

judges are trained to use the full scale (Koenen et al. 1995). Scores from sport

performance are further considered for genetic evaluations, but preselection effects

may influence the estimated breeding values for dressage or jumping performance.

Horses, especially mares, intended for breeding purposes are not regularly seen in


58

riding sport. Additionally, sport scores are only available later in a horse's life,

whereas foal data reduces the generation interval by providing early information.

Therefore evaluation data from foals and broodmares appeared to be a suitable

source of early and barely preselected information and was used in the context of this

study.

Beside the advantage of getting information early, more than half of all foals born

are presented at the foal shows. Currently the foal shows are primarily used to

register the foals and to get some early impression of the progeny of young stallions.

Therefore, large numbers of foals can easily be evaluated under rather standardized

conditions. The foals are presented on their dam's side, so simultaneous evaluation

of active broodmares may be an option as well. Furthermore, evaluations of active

broodmares will make it possible to perform repeatability analyses of the new

movement traits. Suontama et al. (2011) showed for Finnhorse and Standardbred

trotters that subjectively scored conformation traits are moderately heritable in foals

(h²=0.1-0.5) and mares (h²=0.1-0.8). Further they found additive genetic correlations

of 0.6-1.0 between analogous foal and mare traits, implying usability of foal data for

breeding purposes. Given the additive genetic correlations we found for unfavorable

movement characteristics we came to the same conclusion. Horse breeding may

benefit from using detailed movement evaluations obtained in foals as an early

source of information on movement.

Despite existing selection programs and the general breeding progress minor

findings indicating incoordination or impaired balance of different severity were found

in 6.2% of the foals and 5.5% of the mares, respectively presented at foal shows and

studbook inspections of the Oldenburg breeding societies. Relevant influence of

genetic factors on the distributions of imbalance signs could be determined for both

age groups. In the literature, signs corresponding to disorders in hind legs or in the

general motion pattern are considered indicative of impaired balance and

coordination of horses of different ages (Van Biervliet, 2007). These more severe

findings of imbalance were less often documented than changes in the posture or

tone of the tail. However, horses affected by more severe findings were often seen in

combination with at least one other indication of imbalance, particularly findings in the


59

tail, and genetic correlation between findings in the tail and more severe findings are

significantly positive. Neck and tail are considered most important for balancing the

horse`s body during movement (Moore, 2010). Abnormal positions of the neck or

head were hardly seen in the foals and mares, but findings in the tail were seen in

almost every 20th horse. Analyzing variances for mares with detailed movement

evaluations and studbook inspection (SBI) records and mares with MPT records

revealed positive genetic correlations between dressage related characteristics and

unfavorable movements. Selection for favorable movements based on the currently

used trait scores and without consideration of specific movement information may

thus lead to an increase of unfavorable movement characteristics. Absence of

significant differences between the SBI trait correctness of gaits and indications of

imbalance and the tendency to even higher scoring of imbalance-positive mares in

MPT trait trot under rider indicated that the current definitions of gait traits do not

cope with all movement characteristics seen in the presented mares. Furthermore,

significantly positive correlations between breeding values (BV) for IMB and TTP on

the one hand and dressage-related SBI and MPT traits on the other hand. The

results of this study may be interpreted as a hint towards some limit of balancing

capacities which may have been reached in dressage horse breeding. Because of

the fundamental role of the equine back for locomotion, any structural and functional

changes in the back are likely to affect the general motion pattern of the horse,

including its coordination abilities (Van Weeren et al., 2010). Conformational

characteristics favorable for a dressage horse, like a rectangle frame (facilitating

swinging of the back) with a relatively short neck (facilitating elevation), may in

connection with the aptitude to move with much expression overstrain the

mechanisms of coordination. Selection of dressage horses for better scores in SBI

and MPT and without consideration of DME information will therefore bear the risk of

increasing prevalences of indications of imbalance in future generations.

According to the results of the study, selection against unfavorable movement

characteristics is possible in the warmblood horse. Heritabilities of 0.40-0.46 in the

foals and 0.18-0.21 in the mares indicate the relevance of genetic factors for the

development of unfavorable movement characteristics in both age groups and imply


60

that information from detailed movement evaluations may be used for breeding

purposes. Positive genetic correlations between the different indications of imbalance

in foals and mares will facilitate their simultaneous reduction.

Given the positive genetic correlations we found between dressage and

unfavorable movement characteristics, extension of detailed movement evaluations

is recommended to enable considering unfavorable movement characteristics when

making breeding decisions. Warmblood riding horses showing indications of

imbalance during free movement may not necessarily perform worse under rider than

unaffected horses at young age. However, long-term effects of these conditions in

warmblood riding horses are unknown so far. Detailed movement evaluations of foals

and mares will provide a suitable basis for further correlation analyses between

unfavorable movement characteristics and performance on different levels and in

different disciplines of sport.

References

Bhatnagar AS, Lewis RM, Notter DR, Schacht C and Splan RK (2011). Genetic

parameters of foal inspection scores for two North American sporthorse registries.

Livest Sci 140, 88-94

Ducro BJ, Koenen EPC, Van Tartwijk JMFM, Van Arendonk JAM (2007a). Genetic

relations of first stallion inspection traits with dressage and show-jumping

performance in competition of Dutch Warmblood horses. Livest Sci 107, 81-85

Ducro BJ, Koenen EPC, Van Tartwijk JMFM, Bovenhuis H (2007b). Genetic relations

of movement and free-jumping traits with dressage and show-jumping performance

of Dutch Warmblood horses. Livest Sci 107, 227-234.

Koenen EPC., Van Veldhuizen AE, Brascamp EW (1995). Genetic parameters of

linear scored conformation traits and their relation to dressage and show-jumping


61

performance in the Dutch Warmblood riding horse population. Livest Prod Sci 43, 85-

94.

Koenen EPC, Aldridge LI, Philipsson J (2004). An overview of breeding objectives for

Warmblood sport horses. Livest Prod Sci 88, 77-84

Lührs-Behnke H, Röhe R, Kalm E (2006). Genetische Analysen von

Reitsportprüfungen und deren Beziehungen zu Merkmalen der Hengstleistungs- und

Zuchtstutenprüfung. Züchtungskunde 78, 119-128

Moore, J. (2010). General biomechanics: the horse as a biological machine. J Equine

Vet Sci 30, 379-383.

Rustin M, Janssens S, Buys N and Gengler N (2009). Multi-trait animal model

estimation of genetic parameters for linear type and gait traits in the Belgian

warmblood horse. J Anim Breeding and Genetics 126, 378-386.

Stock KF and Distl, O (2006). Genetic correlations between conformation traits and

radiographic findings in the limbs of German Warmblood riding horses. Genetics

Selection Evolution 38, 657-671

Stock KF and Distl O (2007). Genetic correlations between performance traits and

radiographic findings in the limbs of German Warmblood riding horses. J Anim

Science 85, 31-41

Suontama M, van der Werf JHJ, Juga J and Ojala M (2011). The use of foal and

studbook traits in the breeding programmes of Finnhorse and Standardbred trotters.

J Anim Breeding and Genetics 128, 114-123

Thorén Hellsten E, Viklund Å, Koenen EPC, Ricard A, Bruns E, Philipsson J (2006).

Review of genetic parameters estimated at stallion and young horse performance


62

test and their correlations with later results in dressage and show-jumping

competition. Livest Sci 103, 1-12

Van Biervliet, J (2007). An evidence-based approach to clinical questions in the

practice of equine neurology. Vet Clin North Am Equine Pract 23, 317-328

Van Weeren PR, McGowan C and Haussler KK (2010). Development of a structural

and functional understanding of the equine back. Equine Vet J 42 (Supplements 38),

393-400

Viklund Å, Braam Å, Näsholm A, Strandberg E, Philipsson J (2010). Genetic variation

in competition traits at different ages and time periods and correlations with traits at

field tests of 4-year-old Swedish Warmblood horses. Animal , 682-691.

Wallin L, Strandberg E, Philipsson J (2003). Genetic correlations between field test

results of Swedish Warmblood riding horses as 4-year-olds and lifetime performance

results in dressage and show-jumping. Livest Prod Sci 82, 61-71.

63

Chapter 7

Chapter 7 (Summary)

65

7 Summary

Genetic analyses of movement traits in German warmblood horses

Ann-Christin Becker

The breeding goals of warmblood horses today focus on the performance in riding sport

and quality of gaits has considerable impact on the value of a horse. Regardless of the

intended use of the horse, correct gaits and balanced movement belong to the most

important and basic qualities of a riding horse. Findings indicating incoordination or

impaired balance were rarely, but regularly seen in horses of different ages in the

context of breeding events of the Oldenburg breeding societies. The standard evaluation

and selection procedures which are based on subjective scorings of rather generally

defined traits were obviously not suitable to eliminate certain unfavorable movement

characteristics. Knowledge on prevalences and distributions was needed to answer the

question of the possible role of genetic factors. Detailed movement evaluations of foals

and mares were used to define and analyze new movement traits, which may serve as

measures of impaired balance. Furthermore investigations were undertaken analyzing

the correlations between the new assessed movement traits and the standard

conformation and performance traits routinely assessed during studbook inspections

and mare performance tests in the field.

Performance information on 2,758 mares, mostly 3-4 years-olds that had completed

mare performance tests (MPT) was used for genetic analyses focusing on options to

improve existing breeding programs through refined trait definition. For all mares, scores

on a scale from 1 to 10 were available for walk, trot, canter, rideability, and free jumping,

with gait scores representing means from evaluation during free movement (F) and

under rider (R). Distinct F and R gait scores were used to investigate the effect of

evaluation type on variance components. Genetic parameters were estimated with

residual maximum likelihood (REML) in multivariate linear animal models. Heritability

Chapter 7 (Summary)

66

estimates for the MPT traits ranged from 0.19 (rideability) to 0.57 (free-jumping). For the

gaits heritabilities were similar (canter) or higher (walk, trot) for F scores than for

corresponding R scores. The correlations between F and R scores for the same gait

were found to be closer additive genetically (rg = 0.7-0.9) than phenotypically (rp = 0.4-

0.6), but may indicate F and R scores may not represent exchangeable measures of the

same trait. Further correlation analyses revealed moderately to highly positive additive

genetic correlations between gaits and rideability for both F and R scores, whereas

additivee genetic correlations between walk and canter and between trot and free

jumping was relevantly dependent on evaluation type. Because selection of riding

horses represents multiple-trait selection, better reflection of covariances between

selection traits will help maximizing the overall breeding progress. According to our

results, Warmblood breeding may therefore benefit from refinement of trait definition with

clear distinction between gait evaluation during free movement and under rider.

For defining new movement traits detailed movement evaluations of 3,374 warmblood

foals and 2,844 mares were further performed in connection with regular breeding

events of the Oldenburg horse breeding societies in 2009 and 2010. Unfavorable

movement characteristics considered indicative for impaired balance were noted by a

special judge (SJ) and the regular judges of the breeding events (RJ) and served as the

basis for definition of new movement traits. Detailed movement information showed that

more severe findings like irregular motion pattern in hind legs (HM) or irregularity in

general motion pattern (GM) occurred only sporadically (prevalences of 1-2%). Irregular

tail tone or posture (TTP) was documented for 4% of the foals and 5% of the mares,

resulting in prevalences of the comprehensive trait indications of imbalance (IMB) of

6.2% (foals) and 5.5% (mares). Binary coding was used for all traits, and genetic

parameters were estimated bivariately in linear animal models with residual maximum

likelihood (REML). Comparative analyses between judges revealed that differences

between trait definitions of SJ and RJ were larger in the mares than in the foals, but

justified combined use of SJ and RJ information in both age groups. Heritability

estimates for the movement traits ranged on the original scale from 0.02 to 0.26 in the

Chapter 7 (Summary)

67

foals and from 0.03 to 0.12 in the mares, with heritabilities for IMB on the underlying

liability scale of 0.46 (foals) and 0.22 (mares). Comparative analyses between age

groups indicated that common genetic factors may be responsible for findings of

impaired balance in foals and mares.

Information on the new movement traits reflecting unfavorable movement

characteristics for 3,374 foals and 2,844 mares was used for correlation analyses with

conformation information on 1,987 mares from studbook inspections (SBI) in 2009 and

performance information on 2,758 mares from mare performance tests (MPT) in 2000-

2008. Analyses of variance revealed few significant differences between scores for SBI

and MPT traits in mares without and with indications of imbalance (IMB) in general or

specific findings like irregular tail tone or posture (TTP). SBI scores for general

impression and development were significantly lower and MPT scores for trot under rider

tended to be higher in IMB-positive mares. Genetic parameters were estimated in linear

animal models with residual maximum likelihood (REML). Additive genetic correlations

and Pearson correlation coefficients between univariately predicted breeding values

indicated unfavorable genetic correlations of IMB and TTP with dressage related

conformation and performance traits. For SBI and MPT traits we found similarities

between the correlation patterns for DME traits in foals and mares. The results implied

that breeding of dressage horses may benefit from revision of current movement

evaluation and consideration of specific movement characteristics.

69

Chapter 8

Chapter 8 (Zusammenfassung)

71

8 Zusammenfassung

Genetische Analyse von Bewegungsmerkmalen beim Deutschen Warmblut

Ann-Christin Becker

Der Fokus der heutigen, modernen Warmblutpferdezucht liegt auf der Züchtung

leistungsfähiger Sport- und Freizeitpferde. Die Qualität der Bewegungen, die Korrektheit

und Fähigkeit zur Balance ist, unabhängig davon ob es sich um ein Dressur-, Spring-,

Vielseitigkeit- oder Kutschpferd handelt, von elementarer Bedeutung und hat großen

Einfluss auf den Wert eines Pferdes. Entscheidungen zukünftiger Zuchtprogramme und

Anpaarungen werden nicht nur aufgrund der Sporterfolge, sondern im großen Maße

auch aufgrund der Bewertungen und Noten der Zuchtveranstaltungen getroffen. Diese

beginnen früh im Leben eines Pferdes mit den Fohlenschauen. Bei diesen werden die

Fohlen der aktuellen Zuchtsaison nicht nur registriert, sondern auch frei an der Seite der

Stute in Schritt, Trab und im Stand präsentiert und erstmalig in Hinblick auf Typ,

Bewegungen und Korrektheit der Gänge beurteilt und im direkten Vergleich rangiert.

Weitere Zuchttermine sind die Stutbuchaufnahme (SBI), Stutenleistungs (SLP)- sowie

Hengstleistungsprüfungen (HLP). Hier werden in erster Linie junge (3-4 jährige) Pferde

in Hinblick auf ihre Eignung als Zuchtpferd beurteilt.

Im Rahmen der Zuchtveranstaltungen des Verbandes der Züchter des Oldenburger

Pferdes e.V. (OL) und des Springpferdezuchtverbandes Oldenburg International e.V.

(OS) wurden Hinweise auf Koordinations- und Balancestörungen bei vereinzelten

Pferden selten, aber recht regelmäßig gesehen. Die im Rahmen dieser Veranstaltungen

routinemäßig erfassten Merkmale, die unter anderem die Grundlage für

Zuchtentscheidung und Selektion darstellen, sind offenbar in Anzahl oder Detailliertheit

nicht ausreichend, diese unerwünschten Bewegungsmerkmale zu erfassen und

züchterisch zu berücksichtigen. Um sich diesem Problem und der Thematik zu nähern

war es erst einmal nötig Informationen über Prävalenzen und Verteilungen dieser


72

Auffälligkeiten zu erlangen, auch um im Weiteren die mögliche Rolle genetischer

Faktoren zu klären. Die Fohlenschauen sowie die Stutbuchaufnahmen der

Zuchtverbände wurden als geeignet zur Erfassung detaillierter Bewegungsbeurteilungen

erachtet, da, vor allem auf den Fohlentermine, eine große Zahl an Pferden zweier

Altersgruppen (Fohlen, Stuten) unter gleichen Bedingungen präsentiert werden, die

zudem noch den Vorteil einer sehr geringen Vorselektion mit sich brachten. Die

detaillierte Bewegungsbeurteilungen von Fohlen und Stuten wurden dann genutzt um

mögliche neue Bewegungsmerkmale zu definieren. Diese neuen Merkmalsdefinitionen

könnten möglicherweise als Maß für Koordinations- und Balancestörungen im

Bewegungsablauf der Pferde dienen. Desweiteren wurden die Korrelationen zwischen

den neu definierten Bewegungsmerkmalen und den Merkmalen der routinemäßig im

Rahmen der Stutbuchaufnahmen und der Stutenleistungsprüfungen erfassten

Leistungs- und Exterieurmerkmale ermittelt.

Informationen zu Ergebnissen der Stutenleistungsprüfungen lagen für 2758 Stuten vor.

Die Mehrheit dieser Stuten war zum Zeitpunkt der Stutenleistungsprüfung zwischen 3

und 4 Jahren alt. Diese Daten wurden für genetische Analysen genutzt, welche sich auf

Möglichkeiten die bestehenden Zuchtprogramme auf Grundlage der verfeinerten

Merkmalsdefinitionen zu verbessern konzentrierte. Die Grundgangarten Schritt, Trab,

Galopp sowie Rittigkeit und Freispringen wurden auf einer Skala von 1 bis 10 beurteilt.

Die Grundgangarten wurden zunächst jeweils frei (F) und unter dem Reiter (R)

vorgestellt und beurteilt, die Wertnote ergab sich dann aus dem Mittelwert der beiden

Einzelnoten. Die Einzelnoten der Grundgangarten (jeweils F oder R) wurden genutzt um

die Effekte der Art der Vorstellung des Pferdes auf die Varianzkomponenten zu

ermitteln. Die genetischen Parameter wurden mittels REML (residual maximum

likelihood) im multivariaten linearen Tiermodell geschätzt. Die Heritabilitäten der

Stutenleistungsprüfungsmerkmale befanden sich im Bereich 0.19 für das Merkmal

Rittigkeit bis 0.57 für das Merkmal Freispringen. Die Heritabilitäten der Grundgangarten

waren ähnlich für die Gangart Galopp und sogar höher für die F Merkmale Schritt und

Trab im Vergleich zu den R Merkmalen. Die Korrelationen zwischen den F und R


73

Wertnoten für die jeweilige selbe Gangart war additiv-genetisch näher (rg= 0.7-0.9) als

phänotypisch (rp= 0.4-0.6), möglicherweise darauf hinweisend, dass die F und R Noten

nicht ein austauschbares Maß für dasselbe Merkmal darstellen. Weitere

Korrelationsanalysen ergaben moderate bis hohe additiv-genetische Korrelationen

zwischen den Grundgangarten (F sowie R) und dem Merkmal Rittigkeit, wohingegen

additiv-genetische Korrelationen zwischen Schritt und Galopp und zwischen Trab und

Freispringen abhängig vom Beurteilungstyp waren. Da die Selektion zur Züchtung eines

Reitpferdes auf mehreren Merkmalen basiert, wird eine vollständigere Reflektion der

Kovarianzen zwischen Selektionsmerkmalen den generellen Zuchtfortschritt

maximieren. Den Ergebnissen der Studie nach zu urteilen, würde die

Warmblutpferdezucht von einer Verfeinerung der Definition der beurteilten Merkmale mit

einer klaren Trennung zwischen der Beurteilung frei und der Beurteilung unter dem

Reiter profitieren.

Zur Definition neuer Bewegungsmerkmale wurden detaillierte Bewegungsbeurteilungen

von 3374 Fohlen und 2844 Stuten genutzt. Diese Daten wurden im Rahmen der

regulären Zuchtveranstaltungen der Oldenburger Zuchtverbände OL und OS 2009 und

2010 aufgezeichnet. Bewegungsauffälligkeiten, die als hinweisend für Störungen der

Koordination und/oder Balance erachtet wurden, wurden durch einen speziellen

Beobachter (SJ) und die regulären Zuchtrichter (RJ) der beiden Zuchtverbände beurteilt

und notiert und dienten als Basis für die spätere Definition neuer Bewegungsmerkmale.

Diese detaillierten Informationen zeigten, dass schwere Bewegungsauffälligkeiten wie

z.B. unregelmäßige Bewegungsmuster der Hinterhand oder Unregelmäßigkeiten im

generellen Bewegungsablauf seltener (Prävalenzen von 1-2%) waren als leichtere

Bewegungsauffälligkeiten. Auffälligkeiten im Tragen des Schweifes sowie ein fehlender

Tonus und damit ein fehlendes Tragen des Schweifes (TTP) wurden für 4% der Fohlen

und 5% der Stuten notiert. Zusammengefasst ergaben sich somit Prävalenzen für das

generelle Merkmal „Hinweisend auf Imbalance“ (IMB) von 6.2% für die Fohlen und 5.5%

für die Stuten. Alle Merkmale wurden binär codiert aufgezeichnet, die genetischen

Parameter wurden bivariat im linearen Tiermodell mit residual maximum likelihood


74

(REML) geschätzt. Vergleichende Analysen zwischen den Beurteilern (SJ oder RJ)

ergaben, dass Unterschiede zwischen den Merkmalsdefinitionen von SJ und RJ in den

Stuten größer als in den Fohlen war, rechtfertigten aber dennoch eine kombinierte

Nutzung der SJ sowie RJ Informationen in beiden Altersgruppen. Die Schätzungen der

Heritabilitäten für die Gangmerkmale lagen auf der originären Skala zwischen 0.02 und

0.26 bei den Fohlen und zwischen 0.03 und 0.12 bei den Stuten, die Heritabilität für IMB

auf der zugrunde liegenden Skala lag bei 0.46 (Fohlen) und 0.22 (Stuten).

Vergleichende Analysen zwischen den Altersgruppen wiesen darauf hin, dass

gemeinsame genetische Faktoren möglicherweise für die Bewegungsauffälligkeiten in

Fohlen und Stuten verantwortlich sind. Korrelationen zwischen den neuen

Bewegungsmerkmalen und den Standardmerkmalen für Exterieur und Leistung wurden

basierend auf Informationen von 1987 Stuten, präsentiert und beurteilt im Rahmen der

SB, sowie 2758 Stuten präsentiert und beurteilt im Rahmen der MPT, geschätzt. SBI

Stuten wurden im Stand präsentiert, sowie im Schritt und Trab an der Hand vorgeführt.

Bewertet wurden sie durch die Zuchtrichter der Zuchtverbände auf einer subjektiven

Bewertungsskala von 1 bis 10 für die Merkmale Kopf, Hals, Sattellage, Vorderhand,

Hinterhand, Rahmen, Typ, Gesamteindruck und Entwicklung, Schritt, Schwung und

Elastizität, Korrektheit der Gänge und Exterieur (= Kopf, Hals, Sattellage, Vorder- und

Hinterhand, Rahmen). Eine Gesamtnote wurde dann gebildet aus den Einzelmerkmalen

Exterieur, Typ, Gesamteindruck und Entwicklung, Schritt, Schwung und Elastizität und

Korrektheit der Gänge. Die MPT Stuten wurden nach folgenden Merkmalen beurteilt:

Schritt F, Schritt R, Trab F, Trab R, Galopp F, Galopp R, Rittigkeit und Freispringen. Die

Vorgestellung der Merkmale unter dem Reiter fand durch den eigenen Reiter statt, nur

das Merkmal Rittigkeit wurde von einem verbandsinternen, professionellen Reiter

vorgenommen. Die F Merkmale wurden beurteilt während die Stuten sich völlig frei in

der Halle bewegten, ohne dass sie durch eine Präsentation an der Hand beeinflusst

worden sind. Von 2844 Stuten mit detaillieren Bewegungsbeurteilungen lagen für 605

Stuten zusätzliche SBI Informationen und für 471 Stuten zusätzliche MPT Informationen

vor. Vergleichende Varianzanalysen der SBI Ergebnisse zwischen Stuten mit und ohne


75

Bewegungsauffälligkeiten ergaben, dass Stuten, die von schwereren Anzeichen von

Imbalance betroffen waren niedrigere Schätzwerte (Least Square Means, LSM) in allen

SBI Merkmalen aufwiesen als die nicht Auffälligen. Stuten die TTP oder IMB Merkmale

zeigten, hatten ebenso niedrige LSM der SBI Merkmale, mit Ausnahme der Merkmale

Kopf, Hals und Sattellage. Allerdings waren die Unterschiede in vielen Fällen nicht

signifikant, besonders nicht für IMB und TTP. Die LSM der MPT Ergebnissen der Stuten

betroffen von TTP und IMB ergaben kaum Unterschiede zu den nicht betroffenen

Stuten, in nur 3 von 8 MPT Merkmalen hatten die Unauffälligen größere LSM als die

Auffälligen. Genetische Analysen der MPT Merkmale ergaben niedrige bis moderate

Schätzungen der Heritabilität für die SBI Merkmale und moderate Heritabilitäten für

Rittigkeit, Gangmerkmale und Freispringen. Die Heritabilitäten für SBI und MPT

Merkmale geschätzt in univariater sowie bivariater Analyse mit Merkmalen der

detaillierten Bewegungsbeurteilungen (DME) waren sehr ähnlich. Die additiv-

genetischen Korrelationen zwischen SBI und MPT lagen meistens zwischen -0.1 und

0.9, waren in vielen Fällen aber mit hohen Standardfehlern behaftet. Anzeichen für

negative genetische Korrelationen mit IMB und TTP in Fohlen und Stuten wurden

ausschließlich für das MPT Merkmal Freispringen gefunden. Die phänotypischen

Korrelationen der detaillierten Bewegungsbeurteilungsmerkmale mit SBI und MPT

Merkmalen waren niedrig. Der Pearson Korrelationskoeffizient zwischen univariat

bestimmten Zuchtwerten für DME, SBI und MT Merkmale ergab konsistente Ergebnisse

zwischen den Fohlendaten (-0.24 bis 0.26) und den Stutendaten (-0.41 bis 0.43).

Signifikant positive Zuchtwertkorrelationen mit r > 0.3 mit IMB und MPT ergaben sich für

Schwung und Elastizität, Schritt frei, Schritt unter dem Reiter, Trab frei, Trab unter dem

Reiter und Rittigkeit. In Hinblick auf die gefundenen positiven genetischen Korrelationen

zwischen Dressur-assoziierten Merkmalen und Bewegungsauffälligkeiten wird die

Erweiterung der Standardbeurteilungsmerkmale um die DME empfohlen. Diese

unerwünschten Merkmale können so differenziert betrachtet und in zukünftigen

Zuchtentscheidungen berücksichtigt werden. Die Ergebnisse zeigten auch, dass junge

Reitpferde, die Anzeichen von Bewegungsauffälligkeiten in der freien Bewegung


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aufweisen, nicht automatisch auch in ihrer Leistung unter dem Sattel reduziert sein

müssen. Allerdings sind die Langzeiteffekte dieser Störungen bisher nicht analysiert

worden und daher unbekannt. Die Aufnahme detaillierter Bewegungsbeurteilungen in

die routinemäßige Aufnahme von Fohlenbeurteilungs- und Stutenbeurteilungsdaten

stellt eine geeignete Basis für weitere Korrelationsanalysen zwischen unerwünschten

Bewegungsmerkmalen und Leistung auf unterschiedlichen Levels und in

unterschiedlichen sportlichen Disziplinen dar.

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Chapter 9

Chapter 9 (List of publications)

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9 List of publications

Journal articles

Ann-Christin Becker, Kathrin Friederike Stock, Ottmar Distl (2011) Genetic correlations between free movement and movement unde rider in performance tests of German Warmlood horses. Livestock Science 142, 245-252

Ann-Christin Becker, Kathrin Friederike Stock, Ottmar Distl (2012) Genetic analysis of movement traits derived from detailed evaluations of Warmblood foals and mares. Journal of Animal Breeding and Genetics 129, 390-401

Ann-Christin Becker, Kathrin Friederike Stock, Ottmar Distl (2013) Correlations of unfavorable movement characteristics in warmblood foals ad mares with routinely assessed conformation and performance traits. Animal 7, 11-21

Oral presentations

Ann-Christin Becker, Kathrin Friederike Stock, Ottmar Distl (2010) Populationsgenetische Analysen zu detaillierten Bewegungsbeurteilungen bei Stuten und Fohlen. Vortragstagung der DGfZ und GfT am 15.-16. September 2010 in Kiel

Ann-Christin Becker, Kathrin Friederike Stock, Ottmar Distl (2010) Usability of detailed information on movement characteristics of mares and foals for breeding purposes in the German Warmblood horse. 61th Annual meeting of the EAAP, 23 to 27 August 2010 in Heraklion, Greece

Ann-Christin Becker, Kathrin Friederike Stock, Ottmar Distl (2011) Genetic Analysis of movement traits in German Warmblood horses. 62th Annual meeting of the EAAP, 29th of August to 2nd of September in Stavanger, Norway

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Chapter 10

Chapter 10 (Acknowledgement)

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10 Acknowledgements

First of all I would like to thank my supervisor Prof. Dr. Dr. habil. Ottmar Distl for his academic guidance, support and some interesting conversations during the preparation of my thesis.

My deepest gratitude goes to Dr. Kathrin Stock, who became an important confidant and who never lost her optimistic attitude towards my academic skills. I would like to thank her for her patience during the statistical analysis, for her important advices, for her general guidance through the pitfalls of the scientific and everyday life and for many cheering phone calls and conversations at her place.

I would also like to thank Dr. Schulze-Schleppinghoff, Mrs. Katrin Burger, Dr. Hahn and Mr. Wilhelm Weerda of the Verband der Züchter des Oldenburger Pferdes e.V. for making possible this study in the first place, for providing me with everything I needed to perform my thesis and for an educational and wonderful summer with you in 2009.

Very special thanks to my parents and my entire family who always believed in me and my dreams. I would not be where I am today without you and your endless love and support. Thank you so much!

Many thanks go to my dear friends, first and foremost Wenke and Kathi, for their friendship and many wonderful hours, unfortunately happening much too rarely.

My utmost gratitude belongs to my beloved one. I cannot express in words what you mean to me and I am thankful for every single day with you. I would have never reached so far without you, your unconditional support and your infinite love.

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