Abstract

Pituitary pars intermedia dysfunction (PPID), also known as equine Cushing’s disease, is widely reported in middle-aged to older domestic equids, but to date only reported in one non-domestic equid, the onager (Equus hemionus onager).¹ This case series reports clinical, hematologic and pathologic findings consistent with PPID in two additional equid species: one Chapman’s zebra (Equus quagga chapmani) and five Przewalski’s horses (Equus ferus przewalskii). The case series reports basal adrenocorticotropic hormone (ACTH) testing as a method to diagnose and monitor PPID in zoologic equids, and the use of pergolide mesylate at domestic equid doses to reduce basal ACTH concentration and reduce clinical signs associated with PPID. Gross and histopathologic examinations of the pituitary gland in four of these cases revealed either pars intermedia adenomas, or adenomatous hyperplasia, similar to pathologic findings in domestic equids affected by PPID. These findings suggest that clinicians working with non-domestic equids should be aware of this condition and consider screening for it routinely, particularly given that improvements in management and veterinary care for exotic animals are resulting in a more aged captive population. Early diagnosis and treatment of PPID may prevent the development of painful clinical sequelae and therefore improve the welfare of zoo equids.

Acknowledgments

The authors would like to thank Andy Durham, Victoria Copas (Liphook Equine Hospital), David Rendle (Rainbow Equine Hospital) and Boehringer Ingelheim for advice regarding pergolide treatment regimens and possible side effects. The authors thank the veterinary department of the Aspinall Foundation, Kent, UK and are grateful to the keeping staff, veterinary nurse, nutritionists and curatorial team at Marwell Wildlife and Ross Eager, equine farrier. Funding for these veterinary investigations was provided by Marwell Wildlife as part of the clinical veterinary department budget. The authors declare no conflicts of interest.

Literature Cited

1.  Peel AJ, Bouts T, Flach E, Rivers S, Routh A. Pituitary pars intermedia dysfunction (equine Cushing’s disease) in an onager (Equus hemionus onager). J Zoo Wildl Med. 2009;40(4):773–780.