title: Effect of Age, Season, Body Condition, and Endocrine Status on Serum Free Cortisol Fraction and Insulin Concentration in Horses.
abstract: BACKGROUND
  Increased free cortisol fraction is associated with insulin dysregulation (ID) in people with Metabolic Syndrome and Cushing's Disease. Free cortisol has not been investigated in equine endocrine disorders.
  
  
  OBJECTIVE
  (1) In healthy horses, sex, age, body condition score (BCS), and season impact free cortisol; (2) free cortisol is increased in horses with Pituitary Pars Intermedia Dysfunction (PPID) or Equine Metabolic Syndrome (EMS).
  
  
  METHODS
  Fifty-seven healthy horses; 40 horses and ponies with PPID (n = 20) or EMS (n = 20).
  
  
  METHODS
  Prospective study. Serum collected seasonally from healthy animals and archived serum from PPID and EMS animals was analyzed for insulin, total and free cortisol concentrations, and free cortisol fraction (FCF). Linear mixed models were used to determine effects of age, sex, season, and BCS on hormones in controls. Hormone measurements were compared between disease groups and age- and season-matched controls with t-tests. EMS and hyperinsulinemic PPID animals were combined in an ID (hyperinsulinemia) group.
  
  
  RESULTS
  Free cortisol concentrations were increased in overweight/obese controls (0.3 ± 0.1 μg/dL) compared to lean controls (0.2 ± 0.1 μg/dL; P = .017). Mean FCF was significantly higher in animals with PPID (8.8 ± 5.8 μg/dL, P = .005) or ID (8.8 ± 10.2 μg/dL, P = .039) than controls (5.0 ± 0.9 μg/dL), but total cortisol concentrations were similar (P ≥ .350) (PPID: 4.2 ± 4.3 μg/dL; ID: 5.0 ± 4.5 μg/dL; controls: 4.6 ± 1.7 and 5.1 ± 2.1 μg/dL).
  
  
  CONCLUSIONS
  Increased FCF is associated with obesity in healthy horses and with ID (hyperinsulinemia) in horses and ponies with endocrine disease. Decreased plasma cortisol-binding capacity could be a component of these endocrine disorders in horses.
authors: University of Georgia College of Veterinary Medicine, Athens, GA.
authors: K A
authors: KA
authors: Hart
authors: University of Georgia College of Veterinary Medicine, Athens, GA.
authors: D M
authors: DM
authors: Wochele
authors: University of Georgia College of Veterinary Medicine, Athens, GA.
authors: N A
authors: NA
authors: Norton
authors: Oklahoma State College of Veterinary Medicine, Stillwater, OK.
authors: D
authors: D
authors: McFarlane
authors: Auburn University College of Veterinary Medicine, Auburn, AL.
authors: A A
authors: AA
authors: Wooldridge
authors: Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA.
authors: N
authors: N
authors: Frank
mesh_terms: D000375:Aging / Q000097:blood*; D000818:Animals; D001823:Body Composition / Q000502:physiology*; D016022:Case-Control Studies; D005260:Female; D006734:Horse Diseases / Q000097:blood* / Q000378:metabolism; D006736:Horses; D006854:Hydrocortisone / Q000097:blood*; D007328:Insulin / Q000097:blood*; D008297:Male; D024821:Metabolic Syndrome / Q000097:blood / Q000378:metabolism / Q000662:veterinary; D010900:Pituitary Diseases / Q000097:blood / Q000378:metabolism / Q000662:veterinary; D012621:Seasons
chemical_list: D007328:Insulin; D006854:Hydrocortisone
keywords: Equine; Equine Metabolic Syndrome; Insulin resistance; Obesity; Pituitary pars intermedia dysfunction; Steroid