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Int. J. Environ. Res. Public Health 2020, 17, 5661; doi:10.3390/ijerph17165661 www.mdpi.com/journal/ijerph
Review
Psychodynamic Based Equine—Assisted
Psychotherapy in Adults with Intertwined
Personality Problems and Traumatization:
A Systematic Review
Géza Kovács
1,2,
*, Annemiek van Dijke
3
and Marie-Jose Enders-Slegers
1
1
Faculty of Psychology, Open University, Valkenburgerweg 177, 6419 AT Heerlen, The Netherlands;
Marie-Jose.Enders@ou.nl
2
SPEL Psychologen Putten, Garderenseweg 158, 3881 NE Putten, The Netherlands;
g.kovacs@spelpsychologenputten.nl
3
Online poli’s I-psy psyQ Brijder, Parnassia Group, Schipholpoort 20, 2034 MA Haarlem, The Netherlands;
A.vanDijke@psyq.nl
* Correspondence: g.kovacs@spelpsychologenputten.nl
Received: 8 June 2020; Accepted: 31 July 2020; Published: 5 August 2020
Abstract: The growing field of equine-assisted psychotherapy (EAP), a subfield of animal-assisted
psychotherapy (AAP), needs theoretically-based clinical studies. This systematic review examines
the existing clinical studies in adult populations on psychodynamic psychotherapy combined with
equine-assisted psychotherapy. An electronic database search was divided in two studies to identify
publications on 1) EAP combined with psychodynamic psychotherapy and 2) EAP combined to
personality problems and traumatization in order to compile studies by population, intervention,
outcome and therapeutic assets. Study 1 revealed no relevant clinical studies on EAP with a
psychodynamic background with an adult population. Study 2 revealed 12 publications to review
predominantly addressing veterans with PTSD. The methodological limitations of most of the
studies restrain the overall findings on outcome. However, overall positive effects for EAP,
specifically on its experiential features and on finding interpersonal trust for patients, can be
discerned. There is an apparent need for clinical studies meeting methodological standards on
psychodynamic underpinned EAP methodologies in adults with intertwined personality problems
and traumatization.
Keywords: equine-assisted psychotherapy; psychodynamic psychotherapy; personality problems;
traumatization; systematic review
1. Introduction
1.1. Psychodynamic Psychotherapy
Psychodynamic psychotherapy, both time-limited (short-term psychodynamic psychotherapy,
STPP) and open-ended psychodynamic psychotherapy (PPT), is a well-researched treatment
modality and applicable for various mental problems [1–4]. Psychodynamic psychotherapy is an
intersubjective treatment in which the active ingredients are considered to be the enhancement of
mentalization and internalization of a new attachment object through the interpretation of
transference and countertransference experiences between therapist and patient [5]. Enhancing
corrective emotional experiences processed in relation to the therapist entails much of the therapeutic
work [5]. Corrective emotional experience is: “reexperiencing the old, unsettled conflict but with a
Int. J. Environ. Res. Public Health 2020, 17, 5661 2 of 18
new ending”. The emphasis is on the importance of working through painful emotional conflicts by
experiencing new and more adaptive feelings within the therapeutic relationship. For example when
the patient feels anger towards the therapist because the patient feels abandoned due to an upcoming
vacation of the therapist, a corrective emotional experience could be that the patient feels comfortable
to express his anger withstanding the risk from earlier experiences with an important other (usually
the parents) that didn’t accept his anger and the patient was forced to an inadequate coping of the
event.
The use of experiential interventions in order to acquire insight into the underlying patterns
related to patients’ complaints from an interpersonal and intrapersonal perspective is prominent in
the psychodynamic- and to the psychodynamic psychotherapy related schema-focused-
psychotherapy [6]. Meta-analysis on psychodynamic psychotherapy [7] suggests equal efficacy to
other psychotherapies, in addition Town et al. [8] found STPP had robust and persistent effects in
patients with personality disorders.
1.2. Animal-Assisted Psychotherapy
Although seemingly different, animal assisted psychotherapy also focuses on interactions
between individual patient, therapist and in this case animals. Worldwide, a development can be
observed in which animal-assisted interventions can be distinguished within various forms of
assistance [9]. In this paper we explore Animal Assisted (Psycho)therapy (AAP) as defined in the White
Paper of The International Association of Human-Animal Interaction Organizations (IAHAIO; 2014).
Animal-assisted psychotherapy conveys several human-animal interaction theories explaining the
animal-human relationship. It includes biophilia- (emotional connection to other living beings), adult
attachment- (a bi-directional connectivity between humans and animals) and social support theory
(being cared for and loved, and being a member of a network of mutual obligations) in direct relation
to the mutual, embodied attunement of behavior between humans and animals [10].
1.3. Equine-Assisted Psychotherapy
A subcategory of animal-assisted psychotherapy is equine-assisted psychotherapy (EAP) in
which the horse serves as a supporter of psychotherapeutic interventions and as a mediator between
psychotherapist and patient. The horse could be introduced in the psychotherapy as a non-verbal
reciprocal transference- and transitional object in order to find corrective emotional experiences for
the patient. A therapeutic triad is formed in which the animal supports the psychotherapeutic
relationship and psychotherapeutic techniques for patients’ intra- and inter- psychological processes.
Possible useful features of the horse are their social-relational aspects, sensory-intentional aspects,
capability of carrying a person, their vulnerability and power. The explicit features of the horse could
therefore elicit attachment—and mentalization themes on a cognitive-emotional—and bodily-
emotional level next to influencing muscle-motor activity in patients, resembling ‘mother-child
interactions’ [11]. Therefore, in EAP the horse functions as an intersubjective, accessible, safe Other
(Other is used here in the psychodynamic meaning and therefore written with a capital) next to the
psychotherapist through which the patient can learn to understand Others’ minds as well as their
own [12,13]. EAP focuses beside the cognitive level more on the physical and emotional level by the
nonverbal embodied hence experiential approach.Thus facilitating the psychotherapeutic process of
the patient to learn to regulate affects and stress, to enhance self-direction and resilience, essential for
instance in traumatized patients. [14–16].
The observable overlap between the targets proposed in psychodynamic psychotherapy and
those in EAP might suggest that, since psychodynamic psychotherapy is well described and studied,
it could form a fundamental theory for AAP including but not limited to EAP. Earlier conducted
systematic reviews on animal-assisted therapy concluded that there is some evidence for the
effectiveness of AAP but they call the need for comparative studies on AAP and other
psychotherapies, studies that address the psychotherapeutic process in order to understand the
working mechanism, and the development of theories on AAP [17–21].
Int. J. Environ. Res. Public Health 2020, 17, 5661 3 of 18
The growing field of AAP needs questions answered about the efficacy and effectivity and on
how the animal can assist the patient and the therapist during their therapeutic trajectory. To further
the EAP-field, knowledge has to be shared with and about well-defined treatment methods based on
a solid theoretical background. Therefore, we conducted a systematic review to examine the state of
rigorous studies on psychodynamic-based equine-assisted therapies. This examination should be
satisfied if a substantial amount of articles could be retrieved to shed light on psychotherapeutic
assets and clinical relevance of equine-assisted psychotherapy in order to find relevant future
directions for research.
2.
Method
2.1. Existing Clinical Studies on Psychodynamic Based Equine-Assisted Psychotherapy
2.1.1. Study 1: Method
An online search using MedLine and Pre-MedLine (PubMed alike), EMBASE and PsycINFO
search systems was undertaken simultaneously, using the following terms: (equine assisted
psychotherapy OR animal-assisted psychotherapy) AND (psychodynamic psychotherapy OR short-
term psychodynamic psychotherapy). Search terms within each of the categories were linked with
“or,” and larger categories were linked with “and” to capture studies that included at least one search
term from all of the categories.
2.1.2. Inclusion Criteria
Interventions or programs were included if they:
1) Were animal-assisted psychotherapeutic interventions with an emphasis on equine-assisted
therapy with a psychodynamic characteristic for adults 18 years and over and currently
experiencing symptoms or meeting criteria for a mental health condition.
2) Had been published (as journal articles) between 2015 and 2020.
3) Employed an experimental study design with a control or comparison condition, including
randomized trials, matched group designs, and designs in which the sample served as their
own control.
4) Included data on clinical effectiveness (e.g., changes in: interpersonal conflict and
relationships, adaptive functioning, global functioning score, quality of life score, social
skills, in stress response, ability to perform activities of daily living, ability to attend
work/school/volunteering, changes in symptoms like PTSS symptoms, depression, mood,
affect, illness perception).
2.1.3. Exclusion Criteria
Studies were excluded if they did not have a specific focus on adult mental health, did not have
a comparison or control group, or if the intervention did not involve animals (e.g., simulated or
virtual animals).
See Figure 1 for the search history and results following the PRISMA paradigm [22]. Eligibility
assessment was performed independently in unblinded standardized manner by 2 reviewers. The
reviewers had to find consensus about the eligibility of the article. To summarize study outcomes,
the results of each study will be subsequently organized by the most commonly reported outcomes,
such as effect sizes, reported means and standard deviations.
3. Results
No studies were retrieved in this search on rigorous studies on (Short Term) Psychodynamic
Psychotherapy combined with equine-assisted psychotherapy for patients in mental health care who
underwent equine-assisted psychotherapies. In addition no studies were found in this search on
Int. J. Environ. Res. Public Health 2020, 17, 5661 4 of 18
rigorous studies on (Short Term) Psychodynamic Psychotherapy in general combined with animal-
assisted psychotherapy for patient who underwent animal-assisted psychotherapy (AAP).
Figure 1. Flow diagram of the selection process.
3.1. Existing Clinical Studies on Trauma and Personality in Relation to Equine-Assisted Psychotherapy
The lack of results in the first examination warrants a further exploration of the target population
for EAP and psychodynamic psychotherapy. Psychotherapy indication for EAP is often related to
patient reports of a history of psychological trauma and personality problems.
3.1.1. Study 2: Target Population
The proposed target population for psychodynamic psychotherapy and EAP, considering its
overlap, are patients reporting Chronic Early Trauma (CET) in which trauma and personality
problems are intertwined. CET means the harmful psychological, biological and social consequences
of a combination of stressful and potentially traumatic events during childhood. These events are
persistent, long-term, within the interpersonal context and with disruption of developmental stages
Int. J. Environ. Res. Public Health 2020, 17, 5661 5 of 18
resulting in unsafe attachment representations making it difficult for these patients to trust another
person, for example a therapist. While to understand others’ minds as well as their own is important
to process in psychotherapy for patients who suffered traumatization during the developmental
years. The trauma reports have a linear relation to a complexity of commonly associated psychiatric
disorders, ranging from attachment problems, (complex) posttraumatic stress disorder (PTSD),
dissociative disorders, anxiety disorders, alcohol and drug addiction to depression, eating disorders,
somatization disorders, schizophrenia/psychotic episodes and personality disorders (PD) e.g., [23–
28]. Patients with personality disorders are characterized by a rigid pattern of internal experiences
and behavior reflected on cognitive- and inter-personal functioning and on affect-and selfregulation
abilities [29].
3.1.2. Psychodynamic Based EAP with Intertwined Trauma and Personality Problems
The psychodynamic- and to the psychodynamic psychotherapy related schema-focused-
psychotherapy are considered as most applicable for traumatized patients and PD patients. It has an
intensive focus on attachment, problematic mentalization and relational aspects. To acquire insight
into the underlying patterns related to patients’ complaints from an interpersonal- and intrapersonal
perspective the use of experiential interventions is advocated [3,6,23]. The benefits of experiential
interventions for PD patients [6] and the importance of embodied affect-and stress regulation for
traumatized patients, among others namely introduced by Levine [30] and Porges [14], has its place
in the psychodynamic approach. From this perspective equine-assisted psychotherapy could fit this
paradigm. Several theoretical outlines of EAP have been published in which theoretical foundations
are described with reference to psychodynamic-, trauma- attachment- and interpersonal focused
treatment e.g., [11,13,31,32].
Therefore, in the second study we want to investigate the existing clinical studies on trauma
reports/ traumatization and personality problems in relation to equine-assisted psychotherapy to
obtain the state of the amount of research, the populations involved, the form of the EAP intervention,
outcomes and on the therapeutic assets and clinical relevance of equine-assisted psychotherapy. This
examination should be satisfied if a substantial amount of articles could be retrieved to shed light on
therapeutic assets and clinical relevance of studies on trauma reports/ traumatization and personality
problems in relation to equine-assisted psychotherapy in order to find relevant future directions for
research.
3.2. Method
An additional online search (see Figure 2) using Medline and Pre-Medline (PubMed alike),
EMBASE and PsycINFO search systems was undertaken simultaneously, using the same in/exclusion
criteria as in the first study and using the following terms: (animal-assisted psychotherapy OR
equine-assisted psychotherapy) AND (Personality problems OR Traumatization).
Int. J. Environ. Res. Public Health 2020, 17, 5661 6 of 18
Figure 2. Flow diagram of the selection process.
4. Results
We found two articles eligible for review [33,34]. A manual search revealed four more articles
for review [35–38]. Due to their interesting abstracts we added six articles, five which lack control
conditions [39–43] and one article involving adolescents [44]. Table 1 lists the 12 studies included in
this review.
4.1. Population
This review encompasses seven articles (58%) with a patient populations of war veterans with
PTSD [33,37–39,41,43], one article on pain patients
[34], one article on women with social anxiety [35],
one article on substance abuse [36], one article on traumatization in general [42] and one article on
childhood traumatization in adolescents [44].
4.2. Design
Three studies (25%) incorporated a randomized control trial [33–35]. Three studies used a quasi-
randomization to compare the experimental condition with TAU an EAP added or without EAP
[36,38,44]. Six studies used a pre-post test design [37,39–43].
4.3. Intervention
In three studies horseback riding or therapeutic riding was involved [33,36,43]. Three studies
described equine activities as the EAP condition [35,36,40]. One study used activities combined with
mounted work [36]. Three studies explicitly mentioned a psychotherapy orientation, respectively
CBT [35], Attachment-based psychotherapy [44] and Gestalt Therapy (here without psychodynamic
reference to developmental issues) [37]. Three studies incorporated the Eagala model (no mounted
work) [38,41,42]. Body-orientation and herd observation is mentioned in two articles [36,44]. The
duration differed, five articles mentions a 6 week program [33,35,38,41,42], two articles described a 5
day program [37,40], one study used a 8 weeks program [43], in one study a 12 session program is
described [36], one study investigated a 6 months weekly program [39] and one a 12 weekly 2 days
program is mentioned [44].
Int. J. Environ. Res. Public Health 2020, 17, 5661 7 of 18
4.4. Outcome
All articles mention a significant decline in symptoms. Out of the studies with a randomized
control design one article elicits a significant decrease in PTSD symptoms [33], one article describing
significant pain reduction [34], one article mentions a significant reduction of social anxiety [35] and
one study found a significant stronger motivation to stay in therapy for substance abuse [36]. One
study found no significant reduction in PTSD symptoms [38]. Significant increase of resilience was
mentioned in three articles [38,41,44]. All the non-randomized, predominantly pre-post designed,
studies found significant decrease in symptoms, except for one study who found no significant
reduction of PTSD symptoms at 3 months follow up [37]. One study found a significant decrease of
interpersonal sensitivity and phobic complains [40]. Two studies found a decrease in hyperarousal
[40,44] and 1 study found significant improvements on vitality, social functioning and limitations
due to emotional problems over time [43]. One article mentions no effect on respiration rate and
systolic or diastolic blood pressure was found in war veterans with PTSD [40]. One study found no
significant effect of the treatment on physical health, proactive coping, self-efficacy, social support,
or life satisfaction [42].
4.5. Limitations
Overall, a low quantity of identified relevant articles was identified. Five of the total 12 articles
incorporated a randomization and/or control condition, besides there was a lack of information on
the long term effects. There was no blinding strategy involved in the selected articles.
Int. J. Environ. Res. Public Health 2020, 17, 5661 8 of 18
Table 1. Articles included in the review.
Journal Population Design Intervention Outcome and Limitation
Clinical Relevance/
Therapeutic Asset
1. Alfonso, L.,
Llabre, M.,
Fernandez,I. 2015
[35]
The Journal of Science and
Healing, 11/2015, V. 11, 6
Social anxiety
in young
women, N = 12
Randomly assigned to
experimental or a no-
treatment condition.
Pre-post and follow up.
combining equine-assisted
activities and cognitive-
behavioral strategies to reduce
symptoms of social anxiety
Experimental condition
significantly greater
reductions in social anxiety
scores from baseline to
immediate-post and from
baseline to follow-up.
-success experiences
-teambuilding
-bonding with horse
-trust in others
-safe haven to explore
emotions
2. Balluerka,
N., Nekane, M.,
Muela, C., 2015
[44]
Child Abuse & Neglect,
2015, V.50 2015, pp. 193-
205.
adolescents in
residential care
suffered
traumatic
childhood
experiences
with mental
health
problems. N =
63
Sequential two-armed
design, N = 39(19 female
and 20 male; mean age =
15.03) EAP+ TAU and a
control group of 5
female and 19 male;
mean age = 15.67 TAU
EAP involves an ongoing
treatment with clearly
established goals, 12 weeks of
2 days consecutive.
Attachment-based
psychotherapy combined to
EAP. Six thematic blocks: (1)
establishing a secure base, (2)
identification, understanding
and verbalization of emotions,
(3) emotional regulation, (4)
Interpersonal relationships, (5)
self-esteem and self-
competence, and (6) close.
EAP compared TAU:
sign.reduction
hyperactivity, large ES;
adaptive skills sign
improved, large ES;
Sign.improved social
adaption, moderate ES.
Pre-post EAP condition:
sign reduction symptoms
and depression, resp.
moderate and large ES;
improved social skills,
large ES; Interpersonal and
self-esteem, moderate ES
-no randomization,
sequential assignment
-relatively small N
-secure attachment,
relations
-coping skills
- touching and being
touched: reciprocity and
synchrony
- The horse as a mirror of
emotions and behaviors
- Response to success and
failure, resilience
-six clear blocks (structure)
- internal working models
and defense mechanisms.
- the natural environment
generated a sense of
security
-presence of other animals
(i.e., dogs)
3. Bolden L.;
Bentley D.;
Adkins S.;
Jagielski C.;
Schwebel D, 2017
[34]
Archives of Physical
Medicine and
Rehabilitation. 94th
Annual Conference of the
American Congress of
Rehabilitation Medicine,
ACRM 2017. USA. 98
(10) (pp e117), 2017.
Perceived pain
of patients with
spinal cord
injury (SCI). N
= 25
A randomized control
trial. Experimental
condition n = 11
No information on the
intervention
the average pre to post
NRS score decreased for
participants in the
intervention group, but
increased for participants
in the control group
No information on the
intervention
Int. J. Environ. Res. Public Health 2020, 17, 5661 9 of 18
Table 1. Cont.
4. Burton L.,
Burge, M., 2015
[41]
Journal of Investigative
Medicine. Conference:
American Federation for
Medical Research
Western Regional
Meeting, AFMR 2015.
Carmel, CA USA, 63 (1)
(pp 165), 2015
War veterans, N = 10 with
PTSD
Pre-post, 6 weeks
design;
PTSD and resilience
6 weeks EAGALA
sessions, no riding
Reduced PTSD-related
symptoms and increased
adaptive coping skill of
Resilience.
-no control
-small N
-brief intervention reduces
symptoms
-no information on long
term effects
5. Burton, L.,
Qeadan, F.,
Burge M., 2019
[38]
Journal of Integrated
Medicine 2019;17(1):1419
War veterans, N = 20;
experimental condition n =
10, control n = 10
a sequentially
assigned, two-arm
parallel group trial
comparing 6 weeks
of EAP with
standard, previously
established, ongoing
PTSD therapy
Eagala; group;
ground-work
focusing on
metaphors an
awareness of
emotions
Significant decrease PTSD,
increase resilience both
groups. No significant
difference in PTSD,
resilience and salivary
cortisol compared to
control. Low N, no
information on control
condition, short program
-decrease PTSD symptoms
-increase resilience
-experiencing stress relieve
and improved self esteem
-use of metaphors
-use of a group
6. Earles, J.,
Vernon, L., Yetz,
J.,2015
[42]
Journal of Traumatic
Stress. Vol.28(2), 2015,
pp. 149-152
PTSD symptoms
following accident,
physical or sexual assault,
life-threatening illness or
injury and sudden, violent
death. N = 16
Pre-post design; 6
weekly 2-h sessions
measuring:
Posttraumatic stress;
Trauma emotion;
Generalized anxiety;
Depression; Alcohol
use; Physical health;
Mindfulness;
Proactive coping;
Self-efficacy;
Social support; Life
satisfaction;
Optimism
Eagala, no riding;
individual
therapy in group
PTSD symptoms,
emotional distress, anxiety
symptoms, depression
symptoms, and alcohol use
decreased significantly,
increase in mindfulness.
No significant changes in
physical health, proactive
coping, general perceived
self-efficacy, social support,
life satisfaction, or
optimism.
-no control
-no follow up
-less intensive outpatient
program potential to be
effective in reducing
symptoms of anxiety and
depression.
-passive group might have
effects
-non verbal, mindfulness
elements, creating safe
place, setting boundaries
and non critical self-
awareness might be
important ingredients
Int. J. Environ. Res. Public Health 2020, 17, 5661 10 of 18
Table 1. Cont.
7. Johnson et al.,
2018 [33]
Military Medical Research.
5(1):3, 2018
veterans diagnosed
with (PTSD) and/or
traumatic brain
injury (TBI), N = 29
randomized waiting-
list (resp.n = 15, n =
14) controlled design
with repeated
measures
a 6-week therapeutic horseback
riding (THR) program for
decreasing PTSD symptoms and
increasing coping self-efficacy,
emotion regulation, social and
emotional loneliness
significant decrease in
PTSD scores and
loneliness. Coping, self-
efficacy, emotion
regulation trended to
improve. Outcome effects
caused by longer program.
-low N
-short intervention, no
follow up
-not clear to be considered
as psychotherapy
-less PTSS
-bodily
interaction
with horse
-self efficacy
likely to
improve
8. Kern-Godal, A.,
Arnevik, E.,
Walderhaug, E.,
Ravndal, E., 2015
[36]
Addiction science & clinical
practice, 10/2015, V. 10, 1
young hospitalized
substance users N =
107
An intention-to-treat
design, to compare
treatment as usual (n
= 43) with treatment
as usual plus HAT (n
= 65).
EAT as complementary to TAU.
Activity and mounted work, herd
observation and body-oriented
EAT supports motivation
to stay longer in treatment
-therapeutic
alliance
-different
environment
-physical
activity
-individual
attention
-comorbidity
9. Lanning, B.,
Wilson, A., Krenek,
N., Alexander
Beaujean, A., 2017
[43]
Occupational Therapy in
Mental Health, 2017, V.
33, 3
War veterans with
PTSD, N = 51
Pre-post design N =
51; 8-week
therapeutic riding
program
therapeutic riding program
significant decrease in
PTSD symptoms with large
ES, improved social
functioning, vitality, less
interference of emotions on
daily activities, and
increased participation
with large ES.
-no control
-no follow up
-interaction
with horse
-participation
in activities
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Table 1. Cont.
10. Malinowski, K.
et al. 2018 [40]
Journal of Equine
Veterinary Science. 64:17-
26, 2018
PTSD in
Veterans. N = 7 Pre-post design 5 days EAA, involves
equine activities
BSI inventory significantly
reduced except for
interpersonal sensitivity
and phobic anxiety.
Significant reductions
Hyperarousal Symptoms of
PTSD.
HR was significantly
reduced on day 2 involving
grooming and petting in
contrast to more physical
activity other days. No
effect on respiration rate
and systolic or diastolic
blood pressure.
-no information about the
intervention.
-short program
-activities is not therapy
-grooming reduced heart
rate
11. Romaniuk,
Evans, Kidd, 2018
[37]
PLOS ONE, 09/2018,
V.13, 9
Defense Force
veterans and
their partners;
domains of
depression,
anxiety, stress,
PTSD, happiness,
quality of life. N
= 47
A non-controlled,
within-subjects
longitudinal design
(pre- post-interven-
tion and 3 months
follow-up).
Individual and
Couples programs
between subjects
comparison
equine-assisted
therapy (non riding) in
residential program of
5 days Relational
Gestalt Therapy:
exploration of issues,
challenges, and
behaviours and
awareness of
responses e.g., fear,
anxiety, danger.
equine-assisted therapy
useful in the reduction of
depression, anxiety, stress,
PTSD symptoms and the
improvement of happiness
and quality of life. Gains
short-term unless partners
are integrated into the
intervention.
-no explanation about the
effects
-no control
-small N
-short program
-reduction of symptoms
short term
-partners’ secure
attachment conveys a form
of resilience in adversity.
-intervention without
explanation/processing
developmental issues
might influence
sustainability of effects.
12. Shelef, A.,
Brafman, D., Rosing,
T., Weizman, A.,
Stryjer, R., Barak Y.,
2019 [39]
Military Medicine, 2019,
06
Patients with
PTSD (veterans)
N = 13;
measuring PTSD
on daily
functioning and
work
open case series pre-
post design, 6
months
Riding and
groundwork group
therapy, weekly 3
months.
significant improvement in
daily functioning and work
after 6 months.
-no control
-low N
-improvement in
performing daily tasks and
work/study.
-locus of control and trust
through structured
exercises in relation to the
horse.
Int. J. Environ. Res. Public Health 2020, 17, 5661 12 of 18
All studies had a relative small sample size, possibly influencing the external validity, except for
the Kern et al. [36] study with N = 108. Most of the outcomes reported were based on subjective
questionnaires which may create a risk for bias (in either direction depending on the perceptions and
expectations of the participants and clinicians involved), except the studies by Burton et al. [38] who
examined more objective items as cortisol and saliva and likewise Malinowski [40] on respiration rate
and blood pressure. All studies reported p-values to indicate statistical significance, two studies by
Balluerka et al. [44] and Lanning et al. [43] also reported effect sizes.
4.6. Clinical Relevance/Therapeutic Asset
All articles report relatively short programs whether or not as part of ongoing therapy trajectory.
Four articles mention the bodily interaction [33,36,40,44], two in relation to horsebackriding [33,43]
not EAP. Attachment and bonding with horses was mentioned by three studies [35,43,44]. One study
mentioned the attachment between client and involved partner [37]. Providing safe-haven was
reported by two articles [35,42]. The concept of trust/secure adult attachment and therapeutic alliance
was mentioned in five articles [35,36,39,42,44]. The concept of resilience was mentioned by four
articles [37,38,41,44]. The presence of a passive group of clients during EAP was mentioned in one
study [42].
5. Discussion of Studies 1 and 2 in Unison
The growing field of AAP needs questions answered on how the animal assists the patient and
the psychotherapist during their psychotherapy trajectory (mechanisms of change). EAP fits the
psychodynamic psychotherapy realm conveying themes as insecure adult attachment, problematic
mentalization, and experiential interventions considered important to be processed for
psychologically traumatized persons. Therefore with this systematic review we wanted to investigate
the existing studies with adult mental health patients who underwent equine-assisted
psychotherapies with a psychodynamic approach. This examination was satisfactory if a substantial
amount of articles could be retrieved to shed light on psychotherapeutic assets and clinical relevance
of equine-assisted psychotherapy in order to find relevant future directions for research. This goal is
not met.
5.1. Study 1
Our first study of this systematic review revealed no studies on EAP with a psychodynamic
theoretical foundation. On one hand this could be considered fair in the light of the “Dodo-effect”
considering the equal efficacy of all regular psychotherapies [45] implying an irrelevance of
psychotherapeutic school, on the other hand it shows a gap in the light of the benefits of well
described and researched methodologies, not in the least to train and inform psychotherapists (or
other stakeholders) well [46,47].
5.2. Study 2
The second study, in which we reviewed clinical studies on adult patients on trauma and
personality problems in relation to equine-assisted psychotherapy, revealed more eligible studies of
which 50% incorporated a control condition. This examination was satisfactory if a substantial
amount of articles could be retrieved to shed light on psychotherapeutic assets and clinical relevance
of studies on trauma and personality problems in relation to equine-assisted psychotherapy in order
to find relevant future directions for research. This goal is partially met. Much of the studies involved
war veterans with PTSD of which it was unclear whether early childhood trauma was involved. Also
no information on personality disorders or style could be retrieved. The assessment whether PTSD
complaints are rooted in earlier developmental stages of the patient is important in order to define
the route to recovery [25]. We expected more studies with an adult population related to early
childhood trauma given the supposed utility of EAP for this group. The Balluerka et al. [44] and the
Int. J. Environ. Res. Public Health 2020, 17, 5661 13 of 18
Earles et al. [42] publications were the only ones who dealt with a population that could be considered
CET patients, eliciting the need for more studies on EAP and CET population.
Although RCT designs are considered as the golden standard, also non-RCT-designs found in
this review elicit useful research topics even if tentative conclusions, due to the study design, short
programs or overall small sample size, are reported. Specially within the naturalistic social science
and more so in researching animal-assisted psychotherapy blinding procedures run up against
ethical issues, therefore other designs must be taken into account [48]. In line with the literature on
psychotherapy research [48], also research on AAP should emanate from the complexity of clinical
practice, which focuses on the psychotherapeutic process and is driven by theoretical concepts. In
this context, more attention should go to single-case research, systematic observations, clinical
experience and subjective changes in the patient, because it is precisely this the clinician is working
with.
Also in the second study no articles align with/match the psychodynamic psychotherapy realm,
except for the article by Balluerka et al. [44] although it dealt with adolescents. In this study
attachment-based theory was combined to EAP explicitly in which inclusion of the horse
complemented the attachment-based approach [44]. An inclusion criterion in this review was an
adult population, while more studies on AAP and EAP with a population under 18 years of age were
available. It would be interesting to examine the effect of AAP and EAP on the early onset of
traumatization and personality problems.
Overall the studies didn’t show a clear rationale on how and why the horse is included in the
psychotherapy and in some studies one could question whether the intervention could be defined as
psychotherapy.
Remarkable is the relative short duration/low number of sessions of most of the interventions
and with that it is unclear how and if the EAP is embedded in an ongoing treatment trajectory. Since
CET has persistent and long-term consequences one could not assume that for example a 6 weeks
program could elicit adequate recovery for these patients. The results of these very short
interventions [33,35–38,40–42] could only be interpreted as a possible positive impulse for recovery.
The review did show the bodily interaction, physicality and bonding with the horse, possibly
enhancing trust and the psychotherapeutic alliance, as psychotherapeutic assets [33,36,40,44]. In line
with a study by Bamelis et al. [6] who found the involvement of experiential techniques highly
beneficial in psychotherapy for PD, the benefits of equine-assisted psychotherapy could lie in the
embodied experiences which relate to the attachment theory. The severe consequences of adverse
childhood experiences on mental health patients [26,49] and for some possible insufficient alignment
to the more cognitively oriented (and protocol-based) therapy methods [50–52], justify the expansion
of treatment modalities. Different patients may benefit from different approaches or may benefit
through different routes [53], specifically for adults with insecure attachment with traumatization
originating in early (preverbal) development.
With due observance of the limitations of the retrieved studies, a positive trend in outcomes in
favor of EAP can still be observed. Equine-assisted psychotherapy could be an applicable alternative
for hard to reach patients considering its therapeutic asset on trusting others and establishing a
fruitful psychotherapeutic alliance as several studies in this review mentioned [35,36,39,42,44].
For instance, Luyten et al. [1] state that ruptures in the psychotherapeutic alliance are inevitable
with all patients, and that it is the extent to which both psychotherapist and patient manage these
disruptions which relate to psychotherapeutic outcome. The challenge here is to restore epistemic
trust in which experiences of interpersonal relatedness (mutuality and understanding) and self-
definition (separateness) synergistically interact in a mutual facilitating process [1]. The inclusion of
an animal in the psychotherapeutic process could help the restoring of this epistemic trust, crucial for
therapeutic change [2]. Restored epistemic trust helps the patient to reflect in different ways about
him-her self and others, opening the patient up to a social learning process outside the consulting
room, possible with the perceived non-judgmental animal as a means of practice in relation to the
psychotherapist and to the outside world.
Int. J. Environ. Res. Public Health 2020, 17, 5661 14 of 18
5.3. Limitations and Strengths
There are some limitations to be addressed in this review. First, due to the remarkably zero
retrieved studies in the first study, which urged us to add a second search, it might have led to a
heterogeneous search. Although the addressed search items can be considered to be interrelated.
Secondly, the search was restricted to English-language publications, it might be that eligible studies
could be found in other languages. Thirdly, one has to consider the possibility of a publication bias
due to the fact that clinical trials are more likely to be published if the results are statistically
significant, omitting crucial information on non-significant results. Applicability of this review might
be affected by the stringent inclusion criteria which did not deliver many results. However, adding
an additional search with EAP and/or AAP and/or trauma and/or personality brought up studies
with implicit psychodynamic key-aspects shedding light on therapeutic assets and clinical relevance
of equine-assisted psychotherapy. Furthermore, one could consider the strength of this review lying
in the fact that it clearly shows the lack of relevant efficacy studies combining psychodynamic- and
equine-assisted psychotherapy.
6. Conclusions and Recommendations
The conclusions are two-fold. Firstly, in this rather new field of equine-assisted psychotherapy
there are only a few published studies. Most of the literature about equine-assisted psychotherapy
reports about therapies of all kind (by physiotherapists, nurses, social workers, psychologists)
however seldom about equine-assisted psychodynamic psychotherapies. It shows that the AAP and
EAP field is still in its infancy, so it is understandable that there are no relevant efficacy studies
published combining psychodynamic- and equine-assisted psychotherapy between 2015 and 2020
for adult patients.
Therefore, in line with earlier systematic reviews on animal-assisted psychotherapy the
expressed need for theoretical underpinned methodologies studied with comparative designs is still
apparent. The body on evidence on the existing (classical) psychotherapies should form a basis for
research in the field of animal-assisted psychotherapy. We consider animal-assisted psychotherapy
as an (add-on) intervention building on the knowledge of the existing classical psychotherapy
models. Especially considering the advances in neurobiology connected to psychoanalytical thinking,
among others studied by Solms [54], studies on equine-assisted psychotherapy could contribute to
this line of research due to the imposed non-verbal self-regulation strategies [11]. Consistent with
other studies on the mechanisms of change in psychotherapy [47], which findings suggest that
adherence (and competency) to technique and the psychotherapeutic alliance are interdependent and
interrelated in predicting the success of psychotherapy, the establishing of a clear base (here a
psychodynamic approach) is necessary. It helps the psychotherapist to be able to carefully scrutinize
when, why and how specific techniques can be utilized in clinical practice [46]. For that matter also
other theoretical-evidenced based psychotherapies, such as cognitive-behaviour therapy,
complemented by animal-assisted psychotherapy could elicit the development of more personalized
forms of interventions.
Secondly, this review shows that the experiential character of equine-assisted psychotherapy
could be a beneficial factor for patients with intertwined trauma and personality problems. Possibly,
EAP is influencing trust and the psychotherapeutic alliance positively. Also, stronger motivation to
stay in psychotherapy and increase of resilience was associated with EAP. This is relevant as patients
with intertwined trauma and personality problems tend to drop out of psychotherapy and have low
expectations of treatment.
Future Directions
In order to establish EAP as a feasible treatment modality for vulnerable patients, like CET and
to further the field of AAP and EAP, we suggest five future directions. Firstly, as already mentioned,
establishing a clear outline of procedures of an integrated equine-assisted psychodynamic orientation
in clinical studies. A proposed outline should avoid a protocol-based approach but should preferably
Int. J. Environ. Res. Public Health 2020, 17, 5661 15 of 18
enhance the personal approach to psychotherapy. Secondly, to conduct empirical clinical studies
comparing classical psychodynamic orientated psychotherapy to an integrated equine-assisted
psychodynamic psychotherapy for CET patients. Thirdly, focusing on the mechanism of change from
a psychodynamic- and attachment-based view like establishing epistemic trust, embodied affect- and
stress regulation, inter-and intrapersonal deficits such as self-efficacy and resilience in traumatized
patients as several reviewed studies elicited. Fourthly, next to quantitative studies, qualitative
studies, whether or not as part of a mixed model, could draw insight in mechanisms of change from
a patient perspective. Fifthly, we recommend to gain insight in the personality characteristics of
patients who choose EAP allowing for a more transdiagnostic approach of comorbid
symptomatology in order to explore ‘what works for whom’ [46,55].
Author Contributions: G.K., conceptualized and designed the study, analyzed and interpreted data, and wrote
manuscript; A.D., contributed to data collection, analysis and interpretation of data and writing of manuscript;
M.E., provided intellectual support in various steps of the study and contributed to the writing of the
manuscript. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Conflicts of Interest: The authors declare no conflicts of interest.
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