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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
14
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
Chapter 2 (Review on movement disorders in the horse)
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
Chapter 2 (Review on movement disorders in the horse)
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
Chapter 2 (Review on movement disorders in the horse)
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).
Chapter 2 (Review on movement disorders in the horse)
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
Chapter 2 (Review on movement disorders in the horse)
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
Chapter 2 (Review on movement disorders in the horse)
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
Chapter 2 (Review on movement disorders in the horse)
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
Chapter 2 (Review on movement disorders in the horse)
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).
Chapter 2 (Review on movement disorders in the horse)
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
Chapter 2 (Review on movement disorders in the horse)
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.
Chapter 2 (Review on movement disorders in the horse)
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.
Chapter 2 (Review on movement disorders 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
Chapter 2 (Review on movement disorders in the horse)
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.
Chapter 2 (Review on movement disorders in the horse)
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
Chapter 2 (Review on movement disorders in the horse)
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.
Chapter 2 (Review on movement disorders in the horse)
31
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Levine, J.M., Scrivani, P.V., Divers, T.J., Furr, M., Mayhew, I.J., Reed, S., Levine, G.J., Foreman, J.H., Boudreau, C., Credille, B.C., Tennent-Brown, B., Cohen, N.D., 2010. Multicenter case-control study of signalement, diagnostic features, and outcome associated with cervical vertebral malformation-malarticulation in horses. Journal of the American Veterinary Medical Association 237, 812-822.
Mayhew, I.G., De Lahunta, A., Whitlock, R.H., Krook, L., Tasker, J.B., 1978. Spinal cord disease in the horse. Cornell Veterinarian 68 (Supplements 6), 13, 30.
Mayhew, I.G., 1989. Large animal neurology (A handbook for veterinary clinicians). Lea & Febiger, Philadelphia / London, p. 250.
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33
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.
Chapter 2 (Review on movement disorders in the horse)
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.
Chapter 2 (Review on movement disorders in the horse)
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
36
37
Chapter 3
38
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
Chapter 3 (Movement evaluations in mare performance tests)
40
Chapter 3 (Movement evaluations in mare performance tests)
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.
Chapter 3 (Movement evaluations in mare performance tests)
42
43
Chapter 4
44
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
Chapter 4 (Genetic analyses of new movement traits)
46
Chapter 4 (Genetic analyses of new movement traits)
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.
48
49
Chapter 5
50
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
54
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
Chapter 6 (General discussion)
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
Chapter 6 (General discussion)
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
Chapter 6 (General discussion)
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
Chapter 6 (General discussion)
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
Chapter 6 (General discussion)
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.
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63
Chapter 7
64
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.
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69
Chapter 8
70
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
Chapter 8 (Zusammenfassung)
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
Chapter 8 (Zusammenfassung)
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
Chapter 8 (Zusammenfassung)
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
Chapter 8 (Zusammenfassung)
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
Chapter 8 (Zusammenfassung)
76
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.
77
Chapter 9
78
Chapter 9 (List of publications)
79
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
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Chapter 10 (Acknowledgement)
83
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.