A retrospective study of morbidity and mortality in captive Przewalski’s horses (Equus przewalskii) between 1973 and 2021.

Overview

• This study analyzed health and death causes in captive Przewalski’s horses over nearly five decades, using necropsy reports to identify patterns in diseases and mortality factors.
• The goal was to better understand morbidity and mortality to improve management and conservation efforts for this endangered species.

Background and Importance

• Przewalski’s horses, once extinct in the wild by 1996, have been reintroduced into natural habitats starting in 1997, reestablishing free-ranging populations.
• Captive populations remain crucial as reservoirs for the species and support ongoing conservation and reintroduction programs.
• Despite their importance, there had been no systematic and comprehensive pathological analysis of captive Przewalski’s horses prior to this study.

Study Design and Methods

• This was a retrospective study examining necropsy (post-mortem) records of 64 captive Przewalski’s horses from European facilities, covering the years 1973 to 2021.
• Researchers reviewed pathology reports and recorded details such as:
  • Animal characteristics (age, sex)
  • Season of death
  • Whether the animal was euthanized or died naturally
  • Cause of death (COD) and aetiology (cause/origin of disease)
  • Organ systems affected by pathology
  • Incidental or secondary findings
• In total, 105 organ system lesions were identified, indicating multiple health issues in some horses.

Key Findings on Morbidity and Mortality

• Leading Causes of Death:
  • Infectious diseases accounted for 28.1% (18/64) of deaths.
  • Trauma was the next most common cause, contributing to 21.9% (14/64) of deaths.
• Most Frequently Affected Organ Systems:
  • The gastrointestinal (GI) tract was involved in 25.7% (27/105) of lesions, making it the most affected.
  • Musculoskeletal system lesions accounted for 15.2% (16/105) of recorded lesions.
  • Respiratory system lesions represented 13.3% (14/105) of lesions.
• Age- and Sex-related Patterns:
  • Geriatric (older) deaths were predominantly female horses.
  • Adult deaths were more common in males.
  • Euthanasia was performed more frequently on males.
  • Neonates were especially prone to respiratory system lesions.
  • Subadult horses showed higher vulnerability to external causes like intoxications (poisoning) and trauma.

Implications for Management and Conservation

• Main health concerns identified include infectious diseases, trauma, and gastrointestinal issues, highlighting key areas to target in captive care.
• Management factors believed to influence health outcomes include:
  • Peripartum hygiene (care around the time of birth)
  • Social dynamics within captive groups, which could affect stress and injury rates
  • Diet quality and appropriateness
  • Stress management
• Improving husbandry practices tailored to these factors could reduce morbidity and mortality.
• Health monitoring should be enhanced, including standardized pathological protocols, to track and respond to emerging health issues.
• Such improvements in captive population management are crucial to ensure the long-term viability of Przewalski’s horses, supporting future reintroductions and the species’ conservation.

Summary

• This study provides a valuable, comprehensive pathology-based overview of diseases and causes of death in captive Przewalski’s horses over nearly 50 years.
• It identifies infection, trauma, and GI disease as major health threats and reveals notable differences by age and sex.
• The findings emphasize the importance of targeted clinical care, management adaptations, and health surveillance to promote survival and fitness in captive populations.