title: Comparison between blood serum and salivary cortisol concentrations in horses using an adrenocorticotropic hormone challenge.
abstract: BACKGROUND
  In horses, serum cortisol concentration is considered to provide an indirect measurement of stress. However, it includes both free and bound fractions. The sampling method is also invasive and often stressful. This is not the case for salivary cortisol, which is collected using a more welfare-friendly method and represents a part of the free cortisol fraction, which is the biologically active form.
  
  
  OBJECTIVE
  To compare salivary and serum cortisol assays in horses, in a wide range of concentrations, using an adrenocorticotropic hormone (ACTH) stimulation test, in order to validate salivary cortisol for stress assessment in horse.
  
  
  METHODS
  In 5 horses, blood samples were drawn using an i.v. catheter. Saliva samples were taken using swabs. Cortisol was assayed by radioimmunoassay. All data were treated with a regression method, which pools and analyses data from multiple subjects for linear analysis.
  
  
  RESULTS
  Mean ± s.d. cortisol concentrations measured at rest were 188.81 ± 51.46 nmol/l in serum and 1.19 ± 0.54 nmol/l in saliva. They started increasing immediately after ACTH injection and peaks were reached after 96 ± 16.7 min in serum (356.98 ± 55.29 nmol/l) and after 124 ± 8.9 min in saliva (21.79 ± 7.74 nmol/l, P<0.05). Discharge percentages were also different (225% in serum and 2150% in saliva, P<0.05). Correlation between serum and salivary cortisol concentrations showed an adjusted r(2) = 0.80 (P<0.001). The strong link between serum and salivary cortisol concentrations was also estimated by a regression analysis.
  
  
  CONCLUSIONS
  The reliability of both RIAs and regression found between serum and salivary cortisol concentrations permits the validation of saliva-sampling as a noninvasive technique for cortisol level assessment in horses.
authors.affiliation: Faculté de Médecine Vétérinaire, Boulevard de Colonster, Liège, Belgium. marie.peeters@ulg.ac.be
authors.forename: M
authors.initials: M
authors.lastname: Peeters
authors.forename: J
authors.initials: J
authors.lastname: Sulon
authors.forename: J-F
authors.initials: JF
authors.lastname: Beckers
authors.forename: D
authors.initials: D
authors.lastname: Ledoux
authors.forename: M
authors.initials: M
authors.lastname: Vandenheede
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000008:administration & dosage; D000818:Animals; D005260:Female; D006736:Horses; D006854:Hydrocortisone / Q000097:blood / Q000378:metabolism*; D016014:Linear Models; D008297:Male; D011863:Radioimmunoassay / Q000662:veterinary; D012463:Saliva / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone