Effectiveness of animal-assisted interventions for children and adults with post-traumatic stress disorder symptoms: a systematic review and meta-analysis

Figures & data

Figure 1. Flow chart of study selection

Table 1. Characteristics and results of the 8 included controlled studies on PTSD symptom or depression severity

First author, Publication year	Study design	N analysed (AAI/control)	Gender	Age (range, M, SD)	Type of experienced trauma	Participating animals	Treatment provider	AAI terminology	Control intervention	Co-treatment	SMD (95% CI) at end of treatment^a
Bergen-Cico (2018)	Control	48 (34/14)	NR	M = 42, SD = 11.5	War	Dogs	Dog trainer	Therapeutic dog ownership and training	Waiting for service dog and engaging in social programmes (volunteering in a peer support programme)	NR	PTSD: −0.33 (−0.97 to 0.30)
Burton (2019)	Control	20 (11/9)	16m/4f	33–63, M = 47, SD = 14	War	Horses	Occupational therapist, EAGALA-certified with professional horse handler	Equine- assisted psychotherapy	Ongoing PTSD therapy	Ongoing PTSD therapy	PTSD: −0.33 (−1.22 to 0.55)
Dietz (2012)	Control	153 (121/32)	10m/143f	7–17	Sexual abuse	Dogs	Licenced and master’s level clinicians (social work, trained psychologists, counselling)	Animal-assisted therapy	Group PTSD therapy	NR	PTSD: −0.31 (−0.70 to 0.08)
Johnson (2018)	RCT	19 (19/13)	32m/6f^b	29–73, M = 54.35, SD = 12.85	War	Horses	Occupational therapists and PATH-certified riding instructors	Therapeutic horseback riding	Waitlist	NR	PTSD: −0.82 (−1.56 to −0.08)
Mueller (2017)	Control	54 (25/29)	45m/9f	10–18	Physical, sexual, emotional abuse and neglect	Horses	Licenced clinical social worker	Equine-facilitated psychotherapy	Continuation with trauma-focused cognitive behavioural therapy	NR	PTSD: −0.14 (−0.67 to 0.40)
O’Haire (2018)	Control	141 (75/66)	110m/31f	M = 37.1, SD = 8.3	War	Dogs	NA	Service dog	Waiting for service dog; ongoing usual care	Unrestricted access to usual care	PTSD: −0.65 (−0.99 to −0.31)
Whittlesey-Jerome (2014)	Control	13 (6/7)	0m/13f	28–64, M = 43.75	In abusive relationship	Horses	Mental health professional or licenced professional counsellor credentialed by EAGALA	Equine-assisted psychotherapy	Ongoing regular traditional group therapy	Regular traditional group therapy	Depression: −0.32 (−1.42 to 0.78)
Woolley (2004)	Control	21 (11/10)	11m/10f	11–17	Abuse, maltreatment	Farm animals	Staff person or volunteer	Animal-assisted therapy	Conventional psychotherapy	Conventionalpsychotherapy	Depression: −0.03 (−0.88 to 0.83)

N: number of analysed participants in the study; M: mean; SD: standard deviation; SMD: standard mean difference, CI: confidence interval; NR: not reported; m: male; f: female; NA: not applicable; AAI: animal-assisted intervention; RCT: randomized controlled trial; PTSD: post-traumatic stress disorder; EAGALA: equine-assisted growth and learning association; PATH: Professional Association of Therapeutic Horsemanship; ^anegative values indicate superiority of AAI over the comparator; ^bsome studies report gender only for included participants and not for the number of analysed participants.

Table 2. Main results for AAI compared with standard PTSD psychotherapy or waitlist at baseline and at the end of treatment

Treatment effects Comparison & outcome	Number of comparisons	Group difference SMD (95% CI)	P-value for group difference	Heterogeneity (I^2)	Tau^2	P-value for heterogeneity
AAI vs. standard PTSD psychotherapy: PTSD symptom severity
Baseline	3	−0.16 (−0.60 to 0.28)	0.479	50.6%	0.1	0.132
End of treatment	3	−0.26 (−0.56 to 0.04)	0.087	00.0%	0.0	0.865
AAI vs. waitlist: PTSD symptom severity
Baseline	1	−0.04 (−0.68 to 0.60)	0.900	NA	NA	NA
End of treatment	1	−0.82 (−1.56 to −0.98)	0.029	NA	NA	NA
AAI vs. standard PTSD psychotherapy: depression
Baseline	2	−0.48 (−1.16 to 0.19)	0.162	00.0%	0.0	0.875
End of treatment	2	−0.14 (−0.82 to 0.54)	0.687	00.0%	0.0	0.677
Sensitivity analysis Baseline	1	−0.53 (−1.40 to 0.35)	0.238	NA	NA	NA
Sensitivity analysis end of treatment	1	−0.03 (−0.88 to 0.83)	0.951	NA	NA	NA
Getting service dog vs. waiting for service dog: PTSD symptom severity
Baseline	2	−0.08 (−0.38 to 0.21)	0.572	00.0%	0.0	0.934
End of treatment	2	−0.58 (−0.88 to −0.28)	< 0.001	00.0%	0.0	0.390
Drop-outs Comparison
AAI vs. standard PTSD psychotherapy	5	1.99 (0.46 to 8.55)	0.1354	22.8%	0.67	0.269
AAI vs. waitlist	1	10.8 (1.16 to 100.43)	0.036	NA	NA	NA
Getting service dog vs. waiting for service dog	2	3.14 (0.35 to 28.46)	0.310	00.0%	0.0	0.904

AAI: animal-assisted intervention; N: number of included studies; SMD: standard mean difference, OR: odds ratio.

Table 3. Characteristics and results of the 28 studies with pre-post and pre-follow-up effect sizes of AAI regarding PTSD symptom and/or depression severity

First author, Publication year	Study design	N analysed	Gender	Age (range, M, SD)	Type of experienced trauma	Participating animals	Treatment provider	AAI terminology	Pre-post SMC (95% CI) at end of treatment^a	Pre-follow-up SMD (95% CI) at end of treatment^a
Bergen-Cico (2018)	Control	34	NR	M = 42, SD = 11.5	War	Dogs	Dog trainer	Therapeutic dog ownership and training	PTSD: −0.43 (−0.66 to −0.21)	NA
Burton (2019)	Control	11	16m/4f^c	33–63M = 47, SD = 14	War	Horses	Occupational therapist, EAGALA-certified with professional horse handler	Equine-assisted psychotherapy	PTSD: −1.03 (−1.60 to −0.46)	NA
Craven (2013)	Pre-post	5	4m/2f^c	26–66, M = 44, SD = 15.4	War, sexual abuse	Horses	Clinical psychologist/equine specialist, counsellor, equine specialist	Equine-assisted psychotherapy	PTSD: −4.28 (−6.98 to −1.58)	NA
Dietz (2012)	Control	121	10m/143f^c	7–17	Sexual abuse	Dogs	Licenced and master’s level clinicians (social work, trained psychologists, counselling)	Animal-assisted therapy	PTSD: −0.59 (−0.71 to −0.46)	NA
Earles (2015)	Pre-post	16	4m/12f	33–62, M = 51.25, SD = 9.99	Various traumas	Horses	NR	Equine-assisted therapy	PTSD: −0.78 (−1.17 to −0.39) Depression: −0.33 (−0.63 to −0.03)	NA
Faye (2003)	Pre-post	3	6m/7f^c	7–11, M = 9.18, SD = 1.40	Nature	Dolphins	Psychologist	Dolphin interaction	PTSD: −0.94 (−1.94 to 0.05)	NA
Gómez (2016)	Pre-post	5	6m/2f^c	46–76, M = 58, SD = 9.85	War	Horses	Certified PATH International therapeutic riding instructor and certified therapeutic recreation specialist	Equine therapy	PTSD: −0.44 (−1.00 to 0.13)	PTSD: -0.58 (−1.31 to 0.15)
Hamama (2011)	Pre-post^b	9	0m/9f	14–16,M = 14.9, SD = 1.5	Physical or sexual abuse	Dogs	Social work students and professional animal-assisted therapist	Dog-assisted therapy	PTSD: −0.69 (−1.18 to −0.20) Depression: −0.47 (−0.89 to −0.04)	NA
Johnson (2018)	RCT	19	32m/6f^c	29–73, M = 54.35, SD = 12.85	War	Horses	Occupational therapists and PATH-certified riding instructors	Therapeutic horseback riding	PTSD: −0.73 (−1.07 to −0.39)	NA
Kemp (2014)	Pre-post	30	6m/24f	Children: 8–11, M = 9.8, SD = 1.3 Adolescents: 12–17, M = 15.5, SD = 0.8	Physical or sexual abuse, neglect	Horses	Counsellors	Equine-facilitated therapy	PTSD: −3.73 (−4.70 to −2.76) Depression: −1.31 (−1.70 to −0.92)	NA
Kloep (2017)	Pre-post	12	9m/4f^c	Cohort 1: 26–70, M = 44, SD = 15.4 Cohort 2:23–53, M = 36, SD = 13	War	Dogs	NR	Animal-assisted therapy	PTSD: −4.31 (−6.06 to −2.56) Depression: −2.76 (−3.91 to −1.61)	PTSD: −3.92 (−5.67 to −2.17)
Lanning (2013)	Pre-post	7	10m/3f^c	29–52, M = 35.5, SD = 6.9	War	Horses	Veteran volunteers	Equine-assisted activities	Depression: −0.50 (−0.99 to −0.00)	NA
Lanning (2017)	Pre-post	39	33m/18f^c	22–57, M = 36.8, SD = 11.26	War	Horses	Volunteers	Therapeutic horseback riding	PTSD: −0.79 (−1.07 to −0.51)	PTSD: −0.52 (−0.81 to −0.22)
Malinowski (2018)	Pre-post	7	6m/1f	31–68, M = 58, SD = 13.14	War	Horses	Licenced therapist and certified equine specialist	Equine-assisted activities and therapies	PTSD: −1.16 (−1.90 to −0.42)	NA
McCullough (2011)/McCullough (2015)	Pre-post	11	6m/5f	10–18, M = 13.73 SD = 2.83	Physical, sexual, emotional abuse and neglect	Horses	Psychotherapist	Equine-facilitated psychotherapy	PTSD: −0.47 (−0.86 to −0.08)	NA
Mueller (2017)	Control	25	45m/9f^c	10–18	Physical, sexual, emotional abuse and neglect	Horses	Licenced clinical social worker	Equine-facilitated psychotherapy	PTSD: −0.38 (−0.63 to −0.14)	NA
Naste (2018)	Pre-post	2	0m/3f	10–12, M = 11, SD = 1	Sexual abuse, neglect	Horses	Registered mental health practitioner	Equine-facilitated therapy	PTSD: 0.54 (−0.40 to 1.49)	NA
O’Haire (2018)	Control	75	110m/31f^c	M = 37.1, SD = 8.3	War	Dogs	NA	Service dog	PTSD: −1.00 (−1.21 to −0.80)	NA
Romaniuk (2018)	Pre-post	42	30m/17f^c	26–72, M = 46.46, SD = 12, 46	War	Horses	EEA facilitators, certified in the Equine Psychotherapy Institute, accompanied by a psychologist	Equine-assisted therapy	PTSD: Couples: −0.61 (−0.91 to −0.32) Individual: −0.79 (−1.14 to −0.44) Depression: Couples −1.04 (−1.42 to −0.65) Individual −1.18 (−1.57 to −0.78)	PTSD: Couples −0.85 (−1.20 to −0.50) Individual 0.23 (−0.21 to 0.69) Depression: Couples −0.78 (−1.23 to −0.32) Individual 0.30 (−0.27 to 0.87)
Schramm (2015)	Pre-post	6	NR	21–64, M = 47.67, SD = 16.06	Not specified	Sheep	Psychotherapist	Animal-assisted mindfulness training	Depression: −0.10 (−1.72 to −0.27)	NA
Shambo (2010)	Pre-post	6	0m/6f	NR (older than 18)	Interpersonal violence	Horses	NR	Equine-facilitated psychotherapy	Depression: −2.94 (−4.66 to −1.22)	PTSD: −3.22 (−4.94 to −1.50)
Sheade (2015)	Pre-post	3	3m/1f^c	32–67	War	Horses	Principal investigator, Licenced Professional Counsellor (LPC) also PATH certified equine specialist	Relational equine-partnered counselling	PTSD: – 1.64 (−3.11 to −0.18)	NA
Signal (2013)	Pre-post	44	6m/38f	Children: 8–11, M = 9.8, SD = 1.3 Adolescents: 12–17, M = 15.5, SD = 0.8 Adults: 19–50, M = 37	Sexual abuse	Horses	EAGALA counsellors	Equine-facilitated therapy	Depression: Children: −1.82 (−2.53 to −1.11) Youth: −1.31 (−1.85 to −0.76) Adult: −2.19 (−3.05 to −1.33)	NA
Signal (2017)	Pre-post	20	12m/8f	5–12, M = 8.0, SD = 2.0	Sexual abuse	Dogs	Dog handler/owner and specialized RSPCA education officer in conjunction with PH staff	Animal-assisted therapy	PTSD: −0.87 (−1.23 to −0.50)	NA
Steele (2018)	Pre-post	85	60m/25f	22–72, M = 42.94, SD = 11.63	War	Horses	Mental health professional and equine professional	Equine-assisted psychotherapy	PTSD: −0.70 (−0.86 to −0.54) Depression: −0.84 (−1.01 to −0.67)	NA
Vincent (2017)	Pre-post	15	15m/5f^c	31–61+	War	Dogs	Dog trainers/NA	Service dog	PTSD: −1.10 (−1.59 to −0.61) Depression: −0.74 (−1.13 to −0.35)	NA
Whittlesey-Jerome (2014)	Control	6	0m/13f	28–64, M = 43.75	In abusive relationship	Horses	Mental health professional (licenced professional counsellor), or LPC credentialed by EAGALA	Equine-assisted psychotherapy	Depression: −0.37 (−0.84 to −0.09)	NA
Woolley (2004)	Control	11	11m/10f^c	11–17	Abuse, maltreatment	Farm animals	Staff person or volunteer	Animal-assisted therapy	Depression: 0.01 (−0.33 to 0.34)	NA

N: number of analysed participants in the AAI group; M: mean; SD: standard deviation; SMD: standard mean change, CI: confidence interval; NR: not reported; NA: not applicable; AAI: animal-assisted intervention; ^anegative values indicate symptom improvement from beginning to end of treatment; ^bmatching group with no symptoms is not considered as control group, ^csome studies report gender only for included participants and not for the number of analysed participants.

Table 4. Characteristics and results of the 13 studies included only in the narrative review

First author, Publication year	Study design	N analysed (AAI/control)	Gender	Age (range, M, SD)	Type of experienced trauma	Participating animals	Treatment provider	AAI terminology	Results
Balluerka (2014)^a	Control	46 (21/25)	32m/14f	12–17, M = 15.41, SD = 1.65	Not specified	Dogs, horses, farm animals	Psychologist, specialized in AAT	Animal-assisted psychotherapy	Higher attachment security* after AAI compared to before treatment but no effect on other attachment dimensions; no difference between AAI and control group
Balluerka (2015)^a	Control	63 (39/24)	42m/25f^e	12–17, M = 15.27, SD = 1.63	Not specified	Dogs, horses, farm animals	Psychologist, specialized in AAT	Animal-assisted psychotherapy	No difference in clinical symptoms between AAI and control; subscale adaptive skills rated by teachers higher* in AAI compared to control but no difference in other subscales
Beck (2012)	Control	24 (12/12)	17m/7f	AAT: M = 37.08, SD = 11.79 CG: M = 35.5, SD = 9.19	War	Dogs	Dog handler	Animal-assisted therapy	No differences in mood, perceived stress, fatigue, functioning, and participation in everyday activities from pre- to post-assessment but decreased psychological function*, higher work performance* and higher quality of interaction*, no differences between AAI and control group.
Gehrke (2018)	Pre-post	17	NR	NR	War	Horses	Wranglers and counsellors	Equine therapy	Decreased low frequency/high frequency (LF/HF) ratio* in heart rate variability; Improvement in affect* (increase in self-esteem, reduction in irritability and anxiety)
Krause-Parello (2014)^b	RCT	42 (19/23)	2m/40f	5–14, M = 8.91, SD = 2.33	Sexual abuse	Dogs	Therapist, dog and its handler	Animal-assisted intervention	Interaction effect* of dog and interview length on alpha amylase; trend of reduced immunoglobulin A with dog; interaction effect* of dog, age of child and interview length on heart rate
Krause-Parello (2015)^b	RCT	42 (19/23)	2m/40f	5–14, M = 8.91, SD = 2.33	Sexual abuse	Dogs	Therapist, dog and its handler	Animal-assisted intervention	No differences regarding diastolic and systolic blood pressure and heart rate values for both the intervention and control groups; lower cortisol levels after intervention for control group* but not for AAI; no differences in immunoglobulin A before and after intervention or between AAI and control
Krause-Parello (2018)	Control	25 (25/25)	21m/4f	33–86, M = 65.32, SD = 12.26	War	Dog	Psychologist	Animal-assisted intervention	Therapy dog and psychologist both reduce cortisol and heart rate *; no effect on blood pressure, alpha amylase and immunoglobulin A between before and after control or treatment
Kruger (2012)	Pre-post	15	11m/4f	7–17, M = 11.13, SD = 3.11	Not specified	Horses	Licenced mental health professionals	Trauma-focused equine-assisted psychotherapy	Decrease in functional impairment* (increase in subscales school behaviour*, home behaviour*, behaviour towards others*, community behaviour* and moods/emotions*; no change in subscales self-harmful behaviour scale and the problem thinking)
Miller (2018)	Pre-post	31	31m/0f	25–66, M = 41.23, SD = 11.86	Not specified	Dogs	NA	Service animal	Canine presence was not a predictor of reports of nightmares and disturbed dreaming; elevated respiratory event index and lower prior-night sleep respiratory sinus arrhythmia predicted nightmares and disturbed dreams.
Murrow (2013)	Pre-post	9	3m/6f	4–12	Physical or sexual abuse, domestic violence	Dogs	Therapist (not specified) and researcher (dog handler)	Animal-assisted therapy	Change in behaviour towards dog* (some more, some less approach behaviour towards dog); no change in relationship skills
Nevins (2013)	Pre-post	1	1m/0f	52	War	Horses	Certified trainer	Intervention (Saratoga WarHorse Connection method)	Reduced PTSD symptomatology (clinically significant); improvements in depression, resilience, life satisfaction and social support
Rodriguez (2018)^c	Control	73 (45/28)	59m/14f	M = 37.08, SD = 7.81	War	Dogs	NA	Psychiatric service dog	Higher cortisol awakening response*; better health status*; no effect on sleep quality
Woodward (2017)^d	Pre-post	18	18m/0f	M = 39, SD = 13	War	Dogs	NA	Service canine	Attenuated attentional bias towards images of aversive emotive scenes* or angry faces*
Woodward (2017)^d	Pre-post	23	23m/0f	M = 39, SD = 13	War	Dogs	NA	Service dog	Lower sleep heart rate* and greater morning restedness* in presence of the service dog
Wortman (2018)	Pre-post	1	NR	NR	War	Seals	Representative from the VMARC (Veteran and Military Affiliated Research Center)	human–animal interaction	Reduced PTSD symptomatology (clinically significant)
Yarborough (2017)	Pre-post	20	NR	23–67, M = 42, SD = 12	War	Dogs	NA	Service dog	Reduced PTSD symptomatology*; improvements in VR-12 mental component summary*; BASIS depression/functioning subscale*; emotional lability subscale*; activity level*; happiness score* and quality of life*; moderate effect sizes for BASIS substance abuse and interpersonal relationships subscales
Yorke (2013)	Pre-post	4	NR	8–10	Not specified	Horses	NR	human–animal interaction	Mild to moderate symmetry between child-horse pairs

N: number of analysed participants in the study; M: mean; SD: standard deviation; NR: not reported; NA: not applicable; AAI: animal-assisted intervention; AAT: animal-assisted therapy; ^a,b,dboth publications refer to the same study; ^csame study as O’Haire et al. (2015); ^esome studies report gender only for included participants and not for the number of analysed participants; * statistically significant.

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Data availability statement

The data that support the findings of this study are openly available from the Dataverse database at: https://doi.org/10.7910/DVN/MAJSJZ