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Animals : an open access journal from MDPI2025; 15(19); 2779; doi: 10.3390/ani15192779

Physiological and Behavioral Responses of Stabled Horses (Equus caballus) to Three Types of Environmental Enrichment.

Abstract: Small stalls and regulated feedings restrict horses' natural foraging and locomotion, increasing risks to welfare. Environmental enrichment may promote more naturalistic behavioral time budgets, yet little is known about how enrichment type or timing affects physiology and behavior. This study examined nine stabled Quarter Horses provided with hay feeders, activity balls, or mirrors across randomized trials. Each trial included 30 min observations, four times per day, with enrichment removed between sessions and 5-day washouts between trials. Nightwatch Smart Halters™ recorded heart and respiration rates, while behaviors were video-scored using instantaneous scan sampling. Observers were not blind to the treatments. Enrichment effects, item type, time of day, and possible interactions for each variable were tested using a GLMM; Tukey's HSD multiple comparison procedure was used for post hoc comparisons (at ≤ 0.05). Enrichment significantly increased heart rate compared with the control ( = 0.03), indicating heightened arousal, with hay feeders producing the strongest effects. Respiration rate was unaffected. Mirrors reduced evening heart rates compared with other times ( = 0.02). Across treatments, enrichment increased foraging ( = 0.01) and locomotion ( = 0.03), while reducing frustration behaviors ( = 0.03). Hay feeders produced time budgets most similar to wild horses, suggesting greater effectiveness at meeting behavioral needs. Effects were most pronounced at 12:00 h and 16:00 h, outside routine meals. Overall, enrichment may improve physiological and behavioral outcomes, supporting its role in promoting welfare for stabled horses. Larger studies are needed to assess item-specific and long-term impacts.
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Publication Date: 2025-09-23 PubMed ID: 41096375PubMed Central: PMC12523708DOI: 10.3390/ani15192779Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Objective Summary

  • This study investigated how different types of environmental enrichment (hay feeders, activity balls, and mirrors) affect the physiological and behavioral responses of stabled horses.
  • It aimed to determine which enrichment types best support natural behaviors and improve the welfare of horses confined in small stalls.

Background and Rationale

  • Horses kept in small stalls experience restricted movement and feeding opportunities, which can negatively impact their welfare.
  • Environmental enrichment is used to stimulate more natural behaviors, potentially reducing stress and improving overall well-being.
  • Little prior research exists on how different enrichment types and timing influence both physiology (heart rate, respiration) and behavior in stabled horses.

Subjects and Experimental Design

  • Subjects: Nine Quarter Horses were used in the study.
  • Enrichment Types Tested:
    • Hay feeders – designed to encourage natural foraging behavior.
    • Activity balls – objects for physical and mental stimulation.
    • Mirrors – visual stimuli thought to reduce loneliness or boredom.
  • Study Design:
    • Randomized trials were conducted including provision of each enrichment type.
    • Observations were made four times per day, each for 30 minutes.
    • Enrichment items were removed between sessions.
    • Five-day washout periods occurred between trials to prevent carryover effects.

Measurements and Data Collection

  • Physiological Metrics:
    • Heart rate and respiration rates were continuously recorded using Nightwatch Smart Halters™.
  • Behavioral Metrics:
    • Behaviors were video-recorded and scored using instantaneous scan sampling methods.
    • Behaviors of interest included foraging, locomotion, and frustration-related behaviors.
  • Observers were aware of treatment types (not blinded).

Statistical Analysis

  • Generalized Linear Mixed Models (GLMMs) tested effects of:
    • Enrichment presence vs. control (no enrichment).
    • Type of enrichment item.
    • Time of day (when enrichment was provided and observations were made).
    • Interactions between these factors.
  • Post hoc comparisons were made using Tukey’s HSD procedure at a significance threshold of ≤ 0.05.

Key Findings

  • Heart Rate:
    • Enrichment significantly increased heart rate compared to control (p = 0.03), indicating heightened arousal.
    • Hay feeders elicited the strongest increase in heart rate, suggesting greater engagement or stimulation.
    • Mirrors uniquely reduced evening heart rates (p = 0.02), possibly indicating a calming effect during that time.
  • Respiration Rate:
    • No significant effect of enrichment on respiration rate.
  • Behavior:
    • Enrichment increased time spent foraging (p = 0.01) and locomotion (p = 0.03), behaviors closer to those seen in wild horses.
    • Enrichment decreased frustration-related behaviors (p = 0.03), indicating potential reduction of stress or boredom.
    • Hay feeders were most effective at producing naturalistic time budgets, aligning horses’ activity more closely with their species-typical behaviors.
    • Behavioral effects were most pronounced at midday and late afternoon (12:00 and 16:00), times outside routine meal schedules.

Interpretation and Implications

  • Increased heart rate suggests that enrichment elicits physiological arousal, which, combined with increased natural foraging and locomotion, may reflect positive engagement rather than stress.
  • The hay feeder’s effectiveness highlights the importance of providing feeding methods that mimic natural foraging to improve welfare.
  • Reduced frustration behaviors suggest enrichment helps alleviate behavioral signs of poor welfare often seen in stabled horses.
  • The calming effect of mirrors at night could be useful for managing horse stress during low activity periods.
  • The timing of enrichment matters; providing enrichment outside routine feeding times appears most beneficial.

Limitations and Future Directions

  • Small sample size (nine horses) limits generalizability; larger studies are needed to confirm findings.
  • Observers were not blinded, which could introduce bias in behavior scoring.
  • Study focused on short-term effects; long-term impact of enrichment on welfare requires further examination.
  • More detailed comparisons of specific enrichment items and their combinations could optimize welfare protocols.

Conclusions

  • Environmental enrichment, particularly with hay feeders, promotes physiological and behavioral changes consistent with improved welfare in stabled horses.
  • Providing enrichment can help horses express more natural behaviors, reducing stress and frustration linked to confinement.
  • Strategically timed enrichment enhances effectiveness, indicating that modifying management practices can benefit horse well-being.
  • This study supports incorporation of environmental enrichment as a standard welfare practice in horse management.

Cite This Article

APA
Brauns M, Ali A, Berger J, McLean A. (2025). Physiological and Behavioral Responses of Stabled Horses (Equus caballus) to Three Types of Environmental Enrichment. Animals (Basel), 15(19), 2779. https://doi.org/10.3390/ani15192779

Publication

Animals : an open access journal from MDPI
ISSN: 2076-2615
NlmUniqueID: 101635614
Country: Switzerland
Language: English
Volume: 15
Issue: 19
PII: 2779

Researcher Affiliations

Brauns, Miranda
  • Animal Biology Department, University of California Davis, Davis, CA 95616, USA.
Ali, Ahmed
  • Animal and Veterinary Sciences Department, Clemson University, Clemson, SC 29634, USA.
Berger, Jeannine
  • Sacramento Veterinary Behavior Services, Vacaville, CA 95688, USA.
McLean, Amy
  • Animal Science Department, University of California Davis, Davis, CA 95616, USA.

Conflict of Interest Statement

The authors declare no conflicts of interest. The funders had no role in the design of this study; in the collection, analyses, or interpretation of the data; in the writing of this manuscript; or in the decision to publish the results.

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