Pituitary pars intermedia dysfunction (Equine Cushing’s disease) in an onager (Equus hemionus onager).

The research article reports on a notable case of Pituitary pars intermedia dysfunction (PPID), commonly known as Equine Cushing’s disease, observed in a non-domestic equid – a 13-year-old onager at the Zoological Society of London Whipsnade Zoo.

What is the research about?

• The research investigates a case of Pituitary pars intermedia dysfunction (PPID), or Equine Cushing’s disease, in a 13-year-old onager at the Zoological Society of London’s Whipsnade Zoo. Typical hosts of this disease are older horses and ponies, making this specific case unusual considering the onager’s age and non-domestic status.
• The zookeepers noticed symptoms suggestive of PPID such as abnormal hair growth (hirsutism), weight loss, fat redistribution, chronic infections, and laminitis, a painful condition affecting the hooves of the horse-like onager.
• In-depth post-mortem examinations confirmed PPID and identified adenomatous hyperplasia and microadenoma in the pars intermedia region of the onager’s pituitary gland while other potential causes for the observed symptoms were also discussed.

How was the research conducted?

• In order to confirm the suspected diagnosis of PPID, a dexamethasone suppression test was conducted on the onager displaying clinical signs of the disease. This test is typically used to diagnose Cushing’s disease in horses.
• Further post-mortem examinations were also performed, during which the adenomatous hyperplasia and microadenoma in the pars intermedia were detected.

What were the research findings?

• The confirmed diagnosis of PPID in a non-domestic equid like the onager is a significant finding, considering the fact that prior to this, there had not been any reported cases of PPID in captive, non-domestic equids.
• The report brings attention to the possibility that pituitary changes in onagers, like those in older domestic equids, may be positively correlated to age. The authors have suggested that this may be the case although further research is required to confirm such a correlation.
• The study likewise addresses the pituitary gland enlargement observed in three onagers, based on the subjective assessment of an experienced wildlife pathologist, thus indicating an overall prevalence rate of enlargement of 83.3%.
• Researchers also found possible evidence of the condition in the mother of the primary onager, even though she had shown no clinical signs of PPID. Post-mortem examination revealed adenomatous hyperplasia in her pars intermedia region as well, suggesting a plausible occurrence of the disease in her case too.

Research Implications

• The unusual occurrence of PPID in a non-domestic equid signifies the potential reach of the disease across unusual hosts and the need for more comprehensive research and monitoring.
• This research emphasizes the importance of regular veterinary check-ups and timely detection and diagnosis of PPID in captive, non-domestic equids.
• The study’s findings suggest the possible correlation between age and hyperplastic pituitary changes, which necessitates further research.