Emotional Contagion in Human-Horse Interactions: Investigating the Role of Stress and Body Language in Emotional Transfer

1. Introduction

The intricate bond between humans and horses has long fascinated scientists, practitioners, and enthusiasts alike. Horses (Equus caballus) are highly social and perceptive animals, capable of forming complex relationships both within their species and with humans [1]. Research has consistently highlighted the ability of horses to detect and respond to subtle emotional and behavioral cues from humans [2,3,4]. Emotional contagion, the process by which an individual's emotional state influences another's, represents a pivotal dimension of human-horse interaction [5].

The concept of emotional contagion between humans and animals stems from the broader psychological and physiological mechanisms that underlie empathy and social synchronization [6]. Studies on emotional contagion have shown that animals, including horses, can mirror human emotional states through behavioral and physiological changes, such as heart rate variability variability and cortisol levels [1,7]. Horses have demonstrated sensitivity to human facial expressions, vocal tones, and body language, indicating their capacity to perceive and respond to emotional signals [3,8,9,10]. The study of emotional contagion in human-horse interactions has gained increasing attention due to its implications for equine welfare, training, and therapy. Horses are highly sensitive to human emotional states, with research demonstrating that their responses can be assessed through behavioral and physiological indicators such as heart rate variability and cortisol levels [11].

This study is anchored in the hypothesis that humans with elevated levels of emotional arousal, as quantified by heart rate variability monitoring and the State Anxiety Scale [12], are prone to transferring their emotional state to a horse during moments of approach and contact. The underlying premise is that horses, as prey animals, are evolutionarily adapted to detect and react to stress cues from their environment, including those emanating from human handlers [13]. This sensitivity to human emotional states has significant implications for equine welfare, training practices, and the safety of human-equine interactions [14].

The main objective of this research is to elucidate whether emotional contagion occurs from humans to horses during direct contact with stressed human subjects.

Specifically, the study aims to investigate whether this transfer is mediated through human body language and other nonverbal cues. Previous studies have indicated that horses can synchronize their physiological states with humans, particularly during emotionally charged interactions [15,16]. While much of this research has focused on bidirectional interactions, the current study narrows its focus to the unidirectional transfer of stress-related emotions from humans to horses.

Horses’ reactions to human stress can manifest in various ways, including changes in behavior, heart rate variability, and cortisol levels [4,7,17]. For instance, heightened stress in human handlers has been associated with increased heart rate variability and behavioral agitation in horses [15,18]. Body language is a critical medium through which stress and anxiety may be transmitted to horses. As noted by Birke [19], human posture, gestures, and movement patterns can significantly influence equine behavior. Stress-induced changes in body language, such as tense shoulders, abrupt movements, or inconsistent gait, may act as stressors for horses, triggering heightened vigilance or avoidance behaviors [4]. These interactions underscore the need for a deeper understanding of how horses perceive and interpret human nonverbal communication in emotionally charged contexts.

Furthermore, emotional contagion from humans to horses has practical implications for equine welfare and training. Stress in human handlers can compromise the horse’s ability to learn, adapt, and perform effectively [4]. For instance, a stressed handler may inadvertently escalate a horse’s fear response, thereby reducing training efficiency and potentially increasing the risk of accidents [18]. Enhanced understanding of horse–human interactions can contribute to optimizing equine welfare by considering factors such as sensory perception, cognition, and emotional states [20].

The research draws on methodologies that integrate physiological monitoring and behavioral analysis. Heart rate (HR) and heart rate variability (HRV) is used as a quantitative measure of physiological arousal in both humans and horses, providing insights into autonomic nervous system activity [21,22]. Concurrently, video analysis of human and horse interactions captures behavioral indicators of stress, such as ear position, tail movement, and locomotor activity in horses [23]. Facial expressions in horses are widely recognized as indicators of internal states, including pain and emotional responses, making them valuable tools for assessing welfare [24]. Horses can emotionally respond to observing positive and negative horse–human interactions in videos and apply this experience to real-life situations, demonstrating their ability to attribute valence to human experimenters [25].

In summary, this study addresses a critical gap in the literature on interspecies emotional dynamics by focusing on the unidirectional transfer of stress from humans to horses. By exploring the role of body language and physiological signals in mediating this transfer, the research aims to contribute to the growing body of knowledge on human-animal interactions. The findings have the potential to inform best practices in equine management, training, and welfare, ultimately fostering healthier and more harmonious relationships between humans and horses. The hypothesis of this study was that humans with a high level of emotional arousal (stress, anxiety, fear - quantified by an HRV monitor and the State Anxiety Scale) transfer their emotional state to a horse during approach/contact. This study aims to determine if this transfer occurs primarily through body language.

2. Materials and Methods

2.1. Study Design

• Participants and Setting:

This study examines 33 horse-human interactions across five facilities in Transylvania, Romania. The distribution of interactions is as follows: Faculty of Veterinary Medicine, Cluj-Napoca (n=17), Equestrian Center, Sălicea (n=10), Equestrian Center, Micești (n=6)

Human participants were recruited from volunteer students of the University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca and volunteers from equestrian centers. No alterations were made to the horses’ routine activities, such as diet, daily training, or interaction with humans and conspecifics, prior to the study.

To ensure consistency across interactions, all experiments were conducted in a controlled environment. The study took place in enclosed stable areas with minimal external disturbances. Environmental factors such as temperature, lighting, and background noise were monitored and kept within a stable range throughout the study. No other human observers, aside from the research team, were present during the interactions to prevent unintended influences. Horses were given time to acclimate before testing, and interactions were scheduled at similar times of the day to minimize variations in physiological responses due to circadian rhythms.

To reduce the potential influence of olfactory and auditory cues, all human participants were required to follow a standardized protocol before their interactions. Participants refrained from using perfumes, strong-smelling personal care products, or consuming substances that could alter body odor (e.g., caffeine, nicotine) at least 2 hours before testing. Additionally, participants remained silent during interactions to eliminate variations in vocal tone as a confounding factor. The presence of other horses or humans outside the test area was minimized to prevent auditory distractions, ensuring that equine responses were primarily influenced by the visual and tactile aspects of the interaction.

• Experimental Phases:

Preparation of Horses

Horses were placed on the aisle in an empty stable without visual or auditory contact with conspecifics and tied from both sides facing the exit to ensure immobility and human safety. Each horse was fitted with a heart rate variability (HR) monitor and given 30 minutes to acclimate to the environment.

Preparation of Human Participants

Human participants were fitted with a heart rate variability monitor and assessed by a psychologist using the State Anxiety Scale to determine their anxiety levels. Following the assessment, the participants were grouped in two categories: High-anxiety (HA) and Low-anxiety (LA). All participants chosen were unfamiliar with the horses they interacted with.

• Interaction styles:

Constrained Style (CS): Participants wore light sunglasses and a bandana covering the mouth, kept hands in pockets, and approached horses at a metronome-set pace.

The decision to include sunglasses and bandanas as part of the CS condition was based on the necessity to block the possibility of horses decoding human facial cues, which are known to play a significant role in interspecies emotional communication. Research has demonstrated that horses are highly sensitive to human facial expressions and can differentiate between emotional states such as fear, anger, and happiness [26]. By covering the eyes (a key component of emotional expression) with sunglasses and masking the mouth (a region associated with subtle muscle movements that convey affective states) with a bandana, we aimed to minimize visual access to these expressive features. This ensured that any observed differences in horse responses between Free-Style (FS) and Constrained Style (CS) conditions were more likely attributable to body posture and movement rather than facial expression cues. Additionally, previous studies have suggested that horses rely more on facial expressions than vocal cues for emotional recognition [27] further supporting the need to eliminate facial expressivity as a confounding factor.

Free-Style (FS): Participants were free to exhibit natural behaviors, approached at a self-chosen pace, and wore no sunglasses or masks.

• Inclusion and Exclusion Criteria:

For Human Participants

High-Anxiety (HA) Group: Included only if their State Anxiety Scale score was high and their HR was at least 20 bpm above their resting HR (measured 24 hours prior). Participants failing to meet both criteria were excluded.

Low-Anxiety (LA) Group: Included only if their State Anxiety Scale score was low and their HR remained within 2 bpm of their resting HR. Participants outside these parameters were excluded.

For Horses

Excluded if their heart rate did not stabilize within 30 minutes in the experimental stall. Excluded if they exhibited stress behaviors prior to interaction.

• Within-Subjects Approach Rationale:

A within-subjects design was employed to enhance statistical power by minimizing inter-horse variability. Each horse acted as its own control, allowing for direct comparison of responses to high-anxiety (HA) and low-anxiety (LA) interactions.

Sample Size and Counterbalancing: 33 horses

Randomization: Exposure to HA and LA conditions was counterbalanced using a Latin Square Design to control for order effects (Table 1).

2.2. Experimental Procedure

Phase 1: Baseline Measurement

Each horse was placed in the experimental setup for 15 minutes to stabilize HR and baseline HRV and behavioral observations (ethogram scores) were recorded for the last 2 minutes.

Phase 2: Emotional Contagion Experiment

Each horse experienced two experimental conditions in a randomized order:

Condition 1: Interaction with a High-Anxiety Human (HA)

The HA participant approached the horse using firs Free-Style (FS) and then Constrained-Style (CS). Interaction lasted 60 seconds. HRV and behavioral responses were recorded during and after the interaction.

Washout Period (30-60 Minutes)

The horse remained in a quiet stall until HR and behavior returned to baseline.

Condition 2: Interaction with a Low-Anxiety Human (LA)

The LA participant followed the same FS or CS approach. Interaction lasted 60 seconds.

HRV and behavioral responses were recorded during and after the interaction.

2.3. Ethogram

The ethogram categorizes twelve distinct behavioral indicators associated with anxiety in horses, each scored on an ordinal scale to reflect its intensity and duration (Table 2). The ethogram was developed based on previous research and methodologies outlined in the academic works of Kaiser et al. [28], Masko et al. [29], McGreevy et al. [30], Wathan et al. [31], and Dyson et al. [32,33].

3. Results

3.1. Free-Style vs. Constrained Style Comparison

The independent t-tests were conducted to compare the heart rate variability (HRV) and ethogram scores between the HA-FS (free-style) and HA-CS (constrained style) conditions (Table 3). The significant difference in Contact HRV suggests that horses in the HA-FS condition experienced a higher heart rate variability response during contact compared to those in HA-CS.

3.3. Ethogram Score Analysis

The Contact Ethogram Score was significantly different (p = 0.002), meaning that horses in the HA-FS condition exhibited stronger behavioral responses during contact than HA-CS horses. However, Resting Ethogram and Recovery Ethogram Scores were not significantly different, implying that horses behaved similarly at baseline and after recovery (Table 4).

Contact HRV and Contact Ethogram Score showed significant differences between HA-FS and HA-CS. This suggests that the Free-Style condition may have triggered a stronger physiological and behavioral response in the horses compared to the Constrained Style condition.

Resting and Recovery metrics (both HRV and Ethogram scores) were not significantly different, indicating that horses returned to similar physiological and behavioral states after interaction.

3.4. High Anxiety – Constrained Style (HA-CS) vs. Low Anxiety – Constrained Style (LA-CS) Comparison

The independent t-tests were conducted to determine whether the differences in heart rate variability (HRV) and ethogram scores between the interaction when the human participants were constrained by wearing mask, googles and paceing at a metronome in contact conditions (Table 5).

3.5. Low Anxiety – Free-Style (LA-FS) vs. Low Anxiety – Constrained Style (LA-CS) Comparison

The independent t-tests were conducted to determine whether the differences in heart rate variability (HRV) and ethogram scores between the interaction when the human participants/professional horsemen were interacting with horses either in a free-style or in a constrained style in contact conditions (Table 6).

A significant difference was found during contact in ethogram scores between HA-FS and HA-CS conditions (t=3.114, p=0.002) with a large effect size (d=0.81), suggesting that horses exhibited more pronounced behavioral responses when humans expressed stress freely. The difference in heart rate variability (HRV) between HA-FS and HA-CS was also statistically significant (p=0.029), with a moderate effect size (d=0.60). In contrast, comparisons between HA-CS and LA-CS conditions yielded small effect sizes (d=0.12 for HRV, d=0.17 for ethogram scores), indicating minimal differentiation when human body language was restricted.

4. Discussion

The findings of this study indicate that while horses exhibited slightly stronger behavioral responses when interacting with high-anxiety handlers (HA-CS) compared to low-anxiety handlers (LA-CS), these differences were not as pronounced as those observed in free-style (FS) interactions. This suggests that, although some degree of emotional transfer may still occur, the structured body language in controlled setting (CS) conditions serves to mitigate the intensity of behavioral reactions.

The minimal differences observed in heart rate variability (HRV) and ethogram scores during contact interactions suggest that CS interactions effectively reduce emotional transfer from humans to horses. Unlike FS interactions, where horses displayed significant physiological and behavioral changes in response to high-anxiety handlers, CS interactions create a more regulated environment in which horses are less influenced by human emotional states.

Physiologically, heart rate (HR) responses remained stable across HA-CS and LA-CS interactions, indicating that horses did not experience significant stress-related changes due to handler anxiety in CS conditions. Similarly, behavioral responses, as reflected in ethogram scores, showed only a slight increase in HA-CS interactions. However, this difference was minor, suggesting that while horses may still detect subtle cues from anxious handlers, the structured body language in CS conditions minimizes their impact.

Furthermore, CS interactions appear to be an effective method for reducing unintended emotional contagion, making them particularly valuable for handlers who may experience anxiety or nervousness. The absence of statistically significant differences in HRV and behavioral responses between HA-CS and LA-CS conditions further supports this claim. The controlled nature of body language in CS settings likely prevents stress transmission from humans to horses, thereby maintaining a stable physiological and behavioral state in equine participants.

The consistency of HRV responses across LA-FS and LA-CS interactions is also noteworthy. Given that LA participants were experienced horse handlers, it is likely that they naturally regulated their body language, even in FS conditions. This may explain the lack of significant differences in HRV between LA-FS and LA-CS. Experienced handlers tend to exhibit predictable and composed behavior, which likely contributes to stable physiological responses in horses. Additionally, it is plausible that horses had already become accustomed to experienced handling styles, leading to minimal variation in behavioral responses between LA-FS and LA-CS conditions.

These findings have significant implications for equine training, handling, and therapy programs. For equestrians, trainers, and handlers, the study emphasizes the importance of emotional regulation and body control when working with horses, particularly for individuals prone to anxiety. Teaching riders and handlers to adopt a more neutral posture and minimize involuntary stress cues can enhance equine welfare and reduce anxiety-induced behavioral responses. Additionally, equine-assisted therapy programs may benefit from integrating techniques that promote structured, low-expressivity interactions, ensuring that therapy horses do not unnecessarily absorb and reflect human distress.

Training equestrians and therapy practitioners to adopt controlled, predictable movements—similar to those of experienced horse handlers—could be an effective strategy to mitigate stress transfer. Implementing structured training programs that focus on emotional regulation may enhance horse-human interactions and reduce unintended emotional contagion.

Future research should explore additional physiological markers, such as cortisol levels, HRV analysis, and EEG studies, in both humans and horses to gain a deeper understanding of how emotional contagion occurs at a neurophysiological level. Investigating whether structured emotional regulation training for riders improves horse cooperation and reduces behavioral issues could provide further insights into best practices for equine training. Additionally, evaluating the effectiveness of different training methodologies designed to help handlers regulate their emotional expressions may inform future equestrian education and therapeutic interventions.

Practical applications for equine-assisted therapy could incorporate mindfulness techniques for therapy practitioners to prevent unintended stress transmission to therapy horses. Moreover, designing training modules that help therapy horses develop emotional resilience when working with highly stressed clients may improve both horse welfare and the effectiveness of therapy sessions.

These findings suggest that handler experience plays a crucial role in mitigating emotional contagion. Experienced handlers may unconsciously minimize stress cues, thereby reducing the likelihood of transferring anxiety to horses. This reinforces the notion that when humans behave in a consistent and expert manner, horses exhibit stable physiological and behavioral responses, even in less constrained interactions.

5. Conclusions

This study examined the phenomenon of emotional contagion between humans and horses, emphasizing the role of body language in transmitting stress and anxiety. By analyzing heart rate variability (HRV) and ethogram scores, we investigated equine responses to human emotional states in both free-style (FS) and constrained-style (CS) interactions. The findings highlight the significant impact of body language on emotional transfer between humans and horses, with clear differences observed between FS and CS approaches.

The results indicate a significant increase in both HRV and ethogram scores when horses interacted with high-anxiety individuals in the FS condition (HA-FS). This suggests that when humans are free to express emotions through body language, horses are more likely to detect and respond to these cues, leading to heightened physiological and behavioral activation. The increased stress response in horses during HA-FS interactions is consistent with previous research showing that equines, as prey animals, are highly attuned to environmental and social cues, including human emotions.

In contrast, interactions conducted in the CS approach, where human body language was restricted, showed no significant evidence of emotional contagion between humans and horses. Both HA-CS and LA-CS interactions resulted in statistically similar HRV and behavioral responses, indicating that horses did not experience increased stress or anxiety, regardless of the handler’s emotional state.

These findings underscore the importance of controlled and intentional movements when handling horses, suggesting that minimizing human expressiveness can prevent unintended emotional transfer. The structured nature of CS handling appears to act as a buffer against stress contagion, helping to maintain physiological and behavioral stability in horses.

The absence of significant differences between HA-CS and LA-CS conditions further reinforces the idea that horses primarily perceive and respond to human emotions through nonverbal cues rather than merely sensing stress or anxiety at a physiological level. Additionally, the lack of significant differences in HRV and ethogram scores between LA-FS and LA-CS is likely due to the experience level of LA participants. Experienced handlers naturally regulate their body language, even in FS conditions, which reduces variability in how horses perceive them. This explains the consistent physiological responses observed between these conditions.

It is possible that horses were already accustomed to experienced handling styles, leading to minimal behavioral variations between LA-FS and LA-CS. Moreover, experience appears to mitigate emotional contagion, as skilled handlers may unconsciously minimize stress cues. These findings suggest that handler expertise plays a more critical role than anxiety levels in shaping horse responses, acting as a natural buffer against stress transfer. When handlers interact with horses in a knowledgeable and controlled manner, their body language remains neutral across both FS and CS conditions. Emotional contagion is therefore most likely to occur in inexperienced individuals who exhibit uncontrolled body language under stress.