Seasonal variation in serum concentrations of selected metabolic hormones in horses.
BACKGROUND
Determination of adrenocorticotropic hormone (ACTH) concentration is a commonly used test in the evaluation of endocrine causes of equine laminitis, but the concentration in healthy horses can be high at certain times of year, which alters the specificity of the ACTH test.


OBJECTIVE
To determine if circulating concentrations of ACTH, cortisol, glucose, insulin, and thyroxine vary month to month in healthy horses and in horses with equine metabolic syndrome (EMS).


METHODS
Nine healthy adult horses were studied on their farm/stable over the course of 1 year. After the diagnosis of EMS, 10 laminitic horses residing at the same farm/stable were also studied.


METHODS
Prospective study of healthy and laminitic horses. Plasma/serum samples were analyzed for concentrations of hormones and glucose.


RESULTS
ACTH was the only analyte to show a discrete seasonal pattern, with concentrations in healthy and EMS horses frequently outside of the reference range (9-35 pg/mL) in August through October. Insulin was elevated (>40 microIU/mL) in EMS horses during most months and median serum glucose was generally higher in EMS horses (100 mg/dL, range, 76-163 mg/ dL) than in controls (94 mg/dL, range, 56-110 mg/dL), but no seasonal patterns for insulin or glucose were found.


CONCLUSIONS
An increased ACTH concentration in horses in late summer or autumn should be interpreted with caution. In contrast, insulin concentration is maintained within the reference range throughout the year in healthy horses, thus an increased insulin concentration at any time of year should raise suspicions of EMS, ECD, or both.
Place
N J
NJ
Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, NY 14851, USA. njp27@cornell.edu
McGowan
C M
CM
Lamb
S V
SV
Schanbacher
B J
BJ
McGowan
T
T
Walsh
D M
DM
D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000818:Animals; D001786:Blood Glucose; D005534:Foot Diseases / Q000097:blood / Q000378:metabolism; D006724:Hoof and Claw / Q000473:pathology; D006734:Horse Diseases / Q000097:blood* / Q000378:metabolism; D006736:Horses; D006854:Hydrocortisone / Q000097:blood*; D007328:Insulin / Q000097:blood*; D024821:Metabolic Syndrome / Q000097:blood / Q000662:veterinary; D012621:Seasons; D013974:Thyroxine / Q000097:blood*; D013995:Time
D001786:Blood Glucose; D007328:Insulin; D000324:Adrenocorticotropic Hormone; D013974:Thyroxine; D006854:Hydrocortisone