Urinary corticosteroid excretion patterns in the okapi (Okapia johnstoni)

Area of Science:

• Veterinary Medicine
• Animal Physiology
• Endocrinology

Background:

• Stress significantly impacts animal behavior and reproduction, necessitating stress monitoring in captive species.
• Captive breeding programs, like those for okapi, require understanding their stress physiology.
• Noninvasive hormone sampling (urine, feces) is crucial for nondomestic species to avoid additional stress from blood collection.

Purpose of the Study:

• To investigate urinary corticosteroid excretion patterns in okapi.
• To determine the effect of adrenocorticotropic hormone (ACTH) analogue on okapi urinary cortisol levels.
• To establish baseline corticosteroid production and identify circadian rhythms in okapi.

Main Methods:

• Four okapi received saline, 200 IU, or 300 IU of an ACTH analogue via injection, with 24-hour urinary corticosteroid levels compared to baseline.
• Eight okapi were monitored for 5 days to establish normal corticosteroid production patterns.
• Urinary samples were analyzed to quantify corticosteroid levels and identify excretion patterns.

Main Results:

• ACTH analogue injections significantly elevated urinary corticosteroid levels compared to saline and baseline measurements.
• Individual okapi exhibited significant variations in mean corticosteroid levels.
• A distinct circadian pattern was observed, with cortisol levels peaking during daylight hours and declining at night, irrespective of individual or gender.

Conclusions:

• Urinary corticosteroid levels provide a reliable, noninvasive indicator of stress in okapi.
• ACTH analogue administration effectively stimulates corticosteroid excretion in okapi.
• Okapi exhibit a clear circadian rhythm in cortisol production, crucial for interpreting stress hormone data in captive management and conservation efforts.