Sleep architecture and lying behavior in horses across age groups and two housing systems: an overnight non-invasive EEG study.

Overview

• This study examined how different housing environments and age affect sleep patterns and resting behavior in horses using a non-invasive EEG device.
• It highlighted the impact of stable type on sleep architecture and suggested age-related differences, with implications for horse welfare and management.

Research Objectives and Design

• To investigate equine sleep architecture and lying behavior across different housing systems and age groups.
• To utilize a novel, non-invasive EEG mask to record sleep stages in horses without causing disruption.
• To explore potential stress indicators related to housing conditions using heart rate variability (HRV) and fecal cortisol metabolite (FCM) measurements.
• The study involved 10 horses from a university teaching herd observed over four consecutive nights in two housing systems: a large communal stable and two adjacent individual stalls.

Methods and Data Collection

• Electroencephalography (EEG) was employed using a novel, non-invasive mask system to classify sleep stages in real-time.
• Video monitoring facilitated behavioral analysis, particularly focusing on lying behavior such as frequency, duration, and posture.
• Electrocardiography (ECG) was used to assess heart rate variability (HRV), providing objective data on autonomic nervous system activity as a stress indicator.
• Fecal samples were collected to measure cortisol metabolites (FCMs), another physiological marker of stress.

Key Findings: Effects of Housing Systems

• Significant differences in sleep architecture were observed between communal stabling and individual stalls.
• In the individual stalls, horses showed an increase over time in:
  • REM sleep duration
  • The frequency of lying down
• In the large communal stable, horses had:
  • Longer individual lying episodes
  • These findings suggest adaptive behavioral responses dependent on housing environment.
• The results imply that individual stalls may promote more frequent but shorter rest episodes, whereas communal stables result in more prolonged lying bouts.

Key Findings: Age-Related Differences

• Younger horses displayed:
  • Greater amounts of REM sleep and light sleep phases (N1 and N2 stages)
  • More complete and consolidated sleep cycles
  • Longer lying episodes
• Older horses showed reduced quantities of these sleep parameters, indicating age-associated changes in sleep quality and duration.
• These findings highlight the importance of considering age as a factor in equine sleep assessment and care.

Stress and Well-being Indicators

• HRV analysis indicated trends toward increased parasympathetic activity, often associated with relaxation or low stress, especially as horses adapted to their housing conditions.
• Fecal cortisol metabolite levels did not show significant variations, suggesting that housing changes did not markedly increase physiological stress in this sample.
• These outcomes suggest that while housing affects sleep and behavior, it may not provoke acute stress responses detectable by cortisol metabolites.

Implications for Equine Management and Welfare

• Housing environment clearly affects sleep behavior, thus it should be carefully considered in horse management practices to optimize rest.
• Age-related differences in sleep highlight the need for age-specific welfare strategies to ensure adequate sleep quality across life stages.
• The non-invasive EEG mask proved to be a promising tool for monitoring equine sleep without disrupting natural behavior.
• Given that sleep is essential for health and welfare, the study underscores the importance of management approaches that promote sufficient rest.
• Still, normative values for equine sleep stages and validation of EEG protocols in clinical and research settings are needed.
• Further research should also explore how sleep, stress physiology, and overall well-being are interconnected in various housing and environmental contexts.