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Georgia Veterinary Scholars Program

GVSP Summer 2009 Scholars

Georgia Veterinary Scholar	Faculty Mentor
Tesse LeCuyer Washington State University Class of 2012	Dr. Michelle Barton Department of Large Animal Medicine UGA College of Veterinary Medicine

Endogenous Cortisol Secretion Patterns During Health and Illness in Horses and Foals

* Tessa E. LeCuyer, Kelsey A. Hart, Natalie Norton, Michelle H. Barton

Cortisol, the primary mammalian stress hormone, helps support physiologic responses to illness by maintaining blood pressure and regulating inflammation.  Transient cortisol insufficiency occurs frequently in critical illness, and is associated with shock, multiple organ failure, and death.  The purpose of this study was to compare cortisol production rates between healthy horses and foals, as well as between healthy and critically ill horses.  Four adult horses and four 2-4 day-old foals comprised the healthy groups. The sick adult horse group included three horses that met criteria for the systemic inflammatory response syndrome. Blood was collected every 20 minutes for 24 hours in healthy horses and foals and for 12 hours in sick horses for measurement of serum total cortisol concentration using a previously validated chemiluminescent immunoassay.  In healthy horses, mean cortisol concentration was 25.6±6.1 ng/ml and daily cortisol production rate was 0.374±0.09 mg/kg/day, in contrast to 20.1±0.8 ng/ml and 0.671±0.03 mg/kg/day, respectively, in healthy foals. Daily cortisol production rate was significantly higher (P=0.0008) in healthy foals than in adult horses despite comparable mean daily cortisol concentrations. Compared to healthy horses, sick horses had significantly increased (P=0.00003) daily cortisol production rates (1.674±0.152 mg/kg/day).  Daily cortisol production rate and clearance are greater in healthy foals and critically ill adult horses than in healthy adult horses.  Thus, compared to horses, foals with prolonged critical illness may be unable to maintain necessary levels of elevated cortisol synthesis, and may be at increased risk for development of critical illness related cortisol insufficiency and its associated sequelae.