FREE SHIPPING over $40
OVER 9000 FIVE-STAR REVIEWS
5% OFF ALL SUBSCRIPTIONS
100% HAPPINESS GUARANTEE
Analyze Diet
0
Home / Equine Research Bank / J Vet Intern Med / Assessment of baseline adrenocorticotropic hormone and insul...
Journal of veterinary internal medicine2026; 40(1); aalaf056; doi: 10.1093/jvimsj/aalaf056

Assessment of baseline adrenocorticotropic hormone and insulin concentrations in healthy horses in Saskatchewan over a 1-year period.

Abstract: Endocrine disorders in horses, such as pituitary pars intermedia dysfunction and equine metabolic syndrome, rely on hormone testing for diagnosis, but seasonal and regional variabilities highlight the need for locally generated data. Objective: To characterize monthly blood concentrations of ACTH and insulin over 1 year in healthy horses in Saskatchewan. A secondary objective was to assess the association between these outcomes and the following factors: sex, age, breed, pregnancy status, level of exercise, body condition score, and cresty neck score. Methods: Sixty-eight clinically healthy, client- or university-owned horses. Methods: Prospective, observational study. Inclusion criteria: normal physical exams, no travel outside Saskatchewan, no ongoing endocrine or metabolic illness. Samples were collected monthly for 12 months. Blood concentrations of ACTH and insulin were determined by a chemiluminescence assay and associations with the explanatory variables were assessed using generalized estimating equations and generalized linear models. Results: The concentration of ACTH varied by age and month, with older horses showing greater seasonal fluctuations. Maximum ACTH concentration peaked in late summer and early fall, with the older horses and certain breeds showing higher concentrations. Insulin concentrations were highest in August and lowest in December, and consistently higher in Warmbloods than Quarter Horses. Conclusions: Our findings reveal month- and age-related effects on ACTH concentration, and month- and breed-related effects on insulin concentration in healthy horses. These findings support the need to consider temporal and signalment factors when interpreting endocrine test results.
© The Author(s) 2026. Published by Oxford University Press on behalf of the American College of Veterinary Internal Medicine.
Get Full Text
Publication Date: 2026-02-26 PubMed ID: 41742515PubMed Central: PMC12881943DOI: 10.1093/jvimsj/aalaf056Google Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
LinkedInCopy
  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study monitored the blood levels of two key hormones, ACTH and insulin, in healthy horses living in Saskatchewan throughout one year.
  • The goal was to understand how these hormone levels change with time and various horse characteristics to improve diagnosis of endocrine disorders.

Introduction

  • Endocrine disorders in horses, specifically pituitary pars intermedia dysfunction (PPID) and equine metabolic syndrome (EMS), are diagnosed by measuring hormones.
  • Hormone levels can vary by season and region, so local data is necessary for accurate diagnosis.
  • This study aimed to characterize monthly blood levels of ACTH (adrenocorticotropic hormone) and insulin in healthy Saskatchewan horses over one year.
  • A secondary aim was to explore how factors like sex, age, breed, pregnancy, exercise, body condition, and neck fat affect these hormone levels.

Materials and Methods

  • Sixty-eight clinically healthy horses, either client- or university-owned, were enrolled.
  • Selection criteria included thorough physical exams confirming health, no recent travel outside Saskatchewan, and no known endocrine or metabolic diseases.
  • Blood samples were collected monthly for 12 consecutive months.
  • ACTH and insulin concentrations were measured using a chemiluminescence assay, a sensitive laboratory method.
  • Statistical analyses involving generalized estimating equations and generalized linear models were used to test associations between hormones and horse characteristics.

Results

  • ACTH Concentrations:
    • ACTH levels changed depending on the month and the horse’s age.
    • Older horses showed larger seasonal fluctuations in ACTH.
    • ACTH concentrations peaked in late summer and early fall.
    • Certain breeds exhibited higher ACTH levels compared to others.
  • Insulin Concentrations:
    • Insulin levels were highest in August and lowest in December.
    • Warmblood horses consistently showed higher insulin levels than Quarter Horses.

Conclusions

  • The study found that ACTH levels in healthy horses vary by both season (month) and age.
  • Insulin levels vary by season and are influenced by breed.
  • These variations suggest that veterinarians should consider temporal (time of year) and signalment (horse-specific) factors such as age and breed when interpreting hormone test results.
  • Understanding these natural fluctuations aids in better diagnosis and management of endocrine disorders in horses living in Saskatchewan.

Cite This Article

APA
Viviani P, Ragno VM, Parker S, Montgomery JB. (2026). Assessment of baseline adrenocorticotropic hormone and insulin concentrations in healthy horses in Saskatchewan over a 1-year period. J Vet Intern Med, 40(1), aalaf056. https://doi.org/10.1093/jvimsj/aalaf056

Publication

Journal of veterinary internal medicine
ISSN: 1939-1676
NlmUniqueID: 8708660
Country: United States
Language: English
Volume: 40
Issue: 1
PII: aalaf056

Researcher Affiliations

Viviani, Paula
  • Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
  • Large Animal Teaching Hospital, Department of Clinical Sciences, Faculty of Veterinary Medicine, Universidad Nacional del Centro de la Provincia de Buenos Aires, Buenos Aires, Argentina.
Ragno, Valentina M
  • Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
  • Veterinary University Hospital, Faculty of Veterinary Medicine, University of Montreal, Quebec, Canada.
Parker, Sarah
  • Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
  • Center for Applied Epidemiology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Montgomery, Julia B
  • Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
  • Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK, United States.

Grant Funding

  • Townsend Equine Health Research Fund (TEHRF)

Conflict of Interest Statement

The authors declare no conflict of interest.

References

This article includes 57 references
  1. Frank N, Bailey S, Bertin FR. EEG recommendations for the diagnosis and management of equine metabolic syndrome (EMS).. Equine Endocrinology Group Guidelines 2022.
  2. Meyer JC, Hunyadi LM, Ordóñez-Mena JM. The accuracy of ACTH as a biomarker for pituitary pars intermedia dysfunction in horses: a systematic review and meta-analysis.. Equine Vet J 2022;54:457-466.
    doi: 10.1111/evj.13500pubmed: 34428330google scholar: lookup
  3. McFarlane D. Diagnostic testing for equine endocrine diseases.. Vet Clin North Am Equine Pract 2019;35:327-338.
    doi: 10.1016/j.cveq.2019.03.005pubmed: 31076223google scholar: lookup
  4. McGowan CM, Pinchbeck GP, McGowan CM. Prevalence, risk factors and clinical signs predictive for equine pituitary pars intermedia dysfunction in aged horses.. Equine Vet J 2013;45:74-79.
    doi: 10.1111/j.2042-3306.2012.00578.xpubmed: 22594955google scholar: lookup
  5. Durham AE, Frank N, McGowan CM. ECEIM consensus statement on equine metabolic syndrome.. J Vet Intern Med 2019;33:335-349.
    doi: 10.1111/jvim.15423pmc: PMC6430910pubmed: 30724412google scholar: lookup
  6. Carmalt JL, Waldner CL, Allen AL. Equine pituitary pars intermedia dysfunction: an international survey of veterinarians’ approach to diagnosis, management, and estimated prevalence.. Can J Vet Res Rev Can Rech Veterinaire 2017;81:261-269.
    pmc: PMC5644449pubmed: 29081583
  7. Rumfola E, Banse HE, Atkins M, McGowan CM, Ireland JL. Approaches to endocrinopathic laminitis in the field: results of a survey of veterinary practitioners in North America.. J Equine Vet Sci 2022;110:103856.
    doi: 10.1016/j.jevs.2021.103856pubmed: 34958881google scholar: lookup
  8. Tatum RC, McGowan CM, Ireland JL. Evaluation of the sensitivity and specificity of basal plasma adrenocorticotrophic hormone concentration for diagnosing pituitary pars intermedia dysfunction in horses: a systematic review.. Vet J 2021;275:105695.
    doi: 10.1016/j.tvjl.2021.105695pubmed: 34099343google scholar: lookup
  9. McFarlane D, Paradis MR, Zimmel D. The effect of geographic location, breed, and pituitary dysfunction on seasonal adrenocorticotropin and α-melanocyte-stimulating hormone plasma concentrations in horses.. J Vet Intern Med 2011;25:872-881.
    doi: 10.1111/j.1939-1676.2011.0745.xpubmed: 21745243google scholar: lookup
  10. Durham AE, Clarke BR, Potier JFN, Hammarstrand R, Malone GL. Clinically and temporally specific diagnostic thresholds for plasma ACTH in the horse.. Equine Vet J 2021;53:250-260.
    doi: 10.1111/evj.13292pubmed: 32470177google scholar: lookup
  11. Secombe CJ, Tan RHH, Perara DI, Byrne DP, Watts SP, Wearn JG. The effect of geographic location on circannual adrenocorticotropic hormone plasma concentrations in horses in Australia.. J Vet Intern Med 2017;31:1533-1540.
    doi: 10.1111/jvim.14782pmc: PMC5598888pubmed: 28661009google scholar: lookup
  12. Vaughn SA, Norton NA, Hart KA. Circulating hypothalamic-pituitary-adrenal axis hormones and insulin concentrations in horses and ponies.. J Equine Vet Sci 2022;111:103810.
    doi: 10.1016/j.jevs.2021.103810pubmed: 35219029google scholar: lookup
  13. Viviani P, Lavado RA, Chavarria NH, Ragno VM, Montgomery JB. Spring and fall blood concentrations of adrenocorticotropic hormone, insulin, and thyroxine in healthy horses in Saskatchewan.. Can Vet J Rev Veterinaire Can 2024;65:335-342.
    pmc: PMC10945457pubmed: 38562984
  14. Hart K, Bertin FR, Durham A. EEG recommendations on the diagnosis and management of pituitary pars intermedia dysfunction (PPID). Equine Endocrinology Group Guidelines 2023.
  15. Henneke DR, Potter GD, Kreider JL, Yeates BF. Relationship between condition score, physical measurements and body fat percentage in mares.. Equine Vet J 1983;15:371-372.
    doi: 10.1111/j.2042-3306.1983.tb01826.xpubmed: 6641685google scholar: lookup
  16. Carter RA, Geor RJ, Burton Staniar W, Cubitt TA, Harris PA. Apparent adiposity assessed by standardised scoring systems and morphometric measurements in horses and ponies.. Vet J 2009;179:204-210.
    doi: 10.1016/j.tvjl.2008.02.029pubmed: 18440844google scholar: lookup
  17. National Research Council. Nutrient Requirements for Horses. Washington, DC: National Academies Press; 2007.
  18. Copas VEN, Durham AE. Circannual variation in plasma adrenocorticotropic hormone concentrations in the UK in normal horses and ponies, and those with pituitary dysfunction.. Equine Vet J 2012;44:440-443.
    doi: 10.1111/j.2042-3306.2011.00444.xpubmed: 21848531google scholar: lookup
  19. Durham AE, Potier JF, Huber L. The effect of month and breed on plasma adrenocorticotropic hormone concentrations in equids.. Vet J 2022;286:105857.
    doi: 10.1016/j.tvjl.2022.105857pubmed: 35798232google scholar: lookup
  20. Horn R, Stewart AJ, Jackson KV, Dryburgh EL, Medina-Torres CE, Bertin F. Clinical implications of using adrenocorticotropic hormone diagnostic cutoffs or reference intervals to diagnose pituitary pars intermedia dysfunction in mature horses.. J Vet Intern Med 2021;35:560-570.
    doi: 10.1111/jvim.16017pmc: PMC7848300pubmed: 33368633google scholar: lookup
  21. Jacob SI, Geor RJ, Weber PSD, Harris PA, McCue ME. Effect of dietary carbohydrates and time of year on ACTH and cortisol concentrations in adult and aged horses.. Domest Anim Endocrinol 2018;63:15-22.
    doi: 10.1016/j.domaniend.2017.10.005pubmed: 29195115google scholar: lookup
  22. Place NJ, McGowan CM, Lamb SV, Schanbacher BJ, McGowan T, Walsh DM. Seasonal variation in serum concentrations of selected metabolic hormones in horses: seasonal variation in ACTH.. J Vet Intern Med 2010;24:650-654.
    doi: 10.1111/j.1939-1676.2010.0500.xpubmed: 20384949google scholar: lookup
  23. Corpas E, Harman SM, Blackman MR. Human growth hormone and human aging.. Endocr Rev 1993;14:20-39.
    doi: 10.1210/edrv-14-1-20pubmed: 8491152google scholar: lookup
  24. Forsling M, Montgomery H, Halpin D, Windle R, Treacher D. Daily patterns of secretion of neurohypophysial hormones in man: effect of age.. Exp Physiol 1998;83:409-418.
    doi: 10.1113/expphysiol.1998.sp004124pubmed: 9639350google scholar: lookup
  25. Peeters R. Thyroid hormones and aging.. Hormones 2008;7:28-35.
    doi: 10.14310/horm.2002.1111035pubmed: 18359742google scholar: lookup
  26. Born J, Ditschuneit I, Schreiber M, Dodt C, Fehm HL. Effects of age and gender on pituitary-adrenocortical responsiveness in humans.. Eur J Endocrinol 1995;132:705-711.
    doi: 10.1530/eje.0.1320705pubmed: 7788010google scholar: lookup
  27. Cappola AR, Auchus RJ, El-Hajj Fuleihan G. Hormones and aging: an endocrine society scientific statement.. J Clin Endocrinol Metab 2023;108:1835-1874.
    doi: 10.1210/clinem/dgad225pmc: PMC11491666pubmed: 37326526google scholar: lookup
  28. Donaldson MT, McDonnell SM, Schanbacher BJ, Lamb SV, McFarlane D, Beech J. Variation in plasma adrenocorticotropic hormone concentration and dexamethasone suppression test results with season, age, and sex in healthy ponies and horses.. J Vet Intern Med 2005;19:217-222.
    doi: 10.1111/j.1939-1676.2005.tb02685.xpubmed: 15822567google scholar: lookup
  29. Orth DN, Holscher MA, Wilson MG, Nicholson WE, Plue RE, Mount CD. Equine cushing’s disease: plasma immunoreactive proopiolipomelanocortin peptide and cortisol levels basally and in response to diagnostic tests*.. Endocrinology 1982;110:1430-1441.
    doi: 10.1210/endo-110-4-1430pubmed: 6277607google scholar: lookup
  30. Beech J, Boston RC, McFarlane D, Lindborg S. Evaluation of plasma ACTH, α-melanocyte–stimulating hormone, and insulin concentrations during various photoperiods in clinically normal horses and ponies and those with pituitary pars intermedia dysfunction.. J Am Vet Med Assoc 2009;235:715-722.
    doi: 10.2460/javma.235.6.715pubmed: 19751169google scholar: lookup
  31. Cravana C, Fazio E, Ferlazzo A, Medica P. Therapeutic riding horses: using a hypothalamic-pituitary-adrenal axis measure to assess the physiological stress response to different riders. J Vet Behav 2021;46:18-23.
    doi: 10.1016/j.jveb.2021.07.013google scholar: lookup
  32. Marc M, Parvizi N, Ellendorff F, Kallweit E, Elsaesser F. Plasma cortisol and ACTH concentrations in the warmblood horse in response to a standardized treadmill exercise test as physiological markers for evaluation of training status. J Anim Sci 2000;78:1936.
    doi: 10.2527/2000.7871936xpubmed: 10907837google scholar: lookup
  33. Arfuso F, Giannetto C, Bazzano M, Assenza A, Piccione G. Physiological correlation between hypothalamic–pituitary–adrenal axis, leptin, UCP1 and lipid panel in mares during late pregnancy and early postpartum period. Animals 2021;11:2051.
    doi: 10.3390/ani11072051pmc: PMC8300216pubmed: 34359179google scholar: lookup
  34. Hicks GR, Fraser NS, Bertin FR. Changes associated with the peri-ovulatory period, age and pregnancy in ACTH, cortisol, glucose and insulin concentrations in mares. Animals 2021;11:891.
    doi: 10.3390/ani11030891pmc: PMC8003915pubmed: 33804751google scholar: lookup
  35. Fazio E, Medica P, Ferlazzo A. Seasonal patterns of circulating β-endophin, adrenocorticotrophic hormone and cortisol levels in pregnant and barren mares. Bulg J Vet Med 2009;12:125-135.
  36. Ireland JL, Lester A, Banse HE. Factors affecting measurement of basal adrenocorticotropic hormone in adult domestic equids: a scoping review. Vet J 2024;304:106071.
    doi: 10.1016/j.tvjl.2024.106071pubmed: 38341024google scholar: lookup
  37. Borer-Weir KE, Menzies-Gow NJ, Bailey SR, Harris PA, Elliott J. Seasonal and annual influence on insulin and cortisol results from overnight dexamethasone suppression tests in normal ponies and ponies predisposed to laminitis. Equine Vet J 2013;45:688-693.
    doi: 10.1111/evj.12053pubmed: 23521139google scholar: lookup
  38. Hart KA, Wochele DM, Norton NA, McFarlane D, Wooldridge AA, Frank N. Effect of age, season, body condition, and endocrine status on serum free cortisol fraction and insulin concentration in horses. J Vet Intern Med 2016;30:653-663.
    doi: 10.1111/jvim.13839pmc: PMC4913614pubmed: 26860336google scholar: lookup
  39. Karikoski NP, Box JR, Mykkänen AK, Kotiranta VV, Raekallio MR. Variation in insulin response to oral sugar test in a cohort of horses throughout the year and evaluation of risk factors for insulin dysregulation. Equine Vet J 2022;54:905-913.
    doi: 10.1111/evj.13529pmc: PMC9545906pubmed: 34713928google scholar: lookup
  40. Lopes A, Huber L, Durham AE. The seasonality of serum insulin concentrations in equids and the association with breed, age, and sex. J Vet Intern Med 2025;39:e70089.
    doi: 10.1111/jvim.70089pmc: PMC11992590pubmed: 40219807google scholar: lookup
  41. Schreiber CM, Stewart AJ, Kwessi E. Seasonal variation in results of diagnostic tests for pituitary pars intermedia dysfunction in older, clinically normal geldings. J Am Vet Med Assoc 2012;241:241-248.
    doi: 10.2460/javma.241.2.241pubmed: 22765372google scholar: lookup
  42. Vaughn SA, Lemons MB, Hart KA. The effect of season and breed on hypothalamic–pituitary–adrenal axis hormones, metabolic hormones, and oxidative markers in ponies and horses. J Vet Intern Med 2025;39:e70047.
    doi: 10.1111/jvim.70047pmc: PMC11884412pubmed: 40048369google scholar: lookup
  43. Rapson JL, Schott HC, Nielsen BD, McCutcheon LJ, Harris PA, Geor RJ. Effects of age and diet on glucose and insulin dynamics in the horse. Equine Vet J 2018;50:690-696.
    doi: 10.1111/evj.12812pubmed: 29356053google scholar: lookup
  44. Pratt-Phillips S. Effect of exercise conditioning on countering the effects of obesity and insulin resistance in horses—a review. Animals 2024;14:727.
    doi: 10.3390/ani14050727pmc: PMC10931081pubmed: 38473112google scholar: lookup
  45. Conn VS, Koopman RJ, Ruppar TM, Phillips LJ, Mehr DR, Hafdahl AR. Insulin sensitivity following exercise interventions: systematic review and meta-analysis of outcomes among healthy adults. J Prim Care Community Health 2014;5:211-222.
    doi: 10.1177/2150131913520328pmc: PMC4393364pubmed: 24474665google scholar: lookup
  46. Lakka TA, Laaksonen DE. Physical activity in prevention and treatment of the metabolic syndrome. Appl Physiol Nutr Metab 2007;32:76-88.
    doi: 10.1139/h06-113pubmed: 17332786google scholar: lookup
  47. Way KL, Hackett DA, Baker MK, Johnson NA. The effect of regular exercise on insulin sensitivity in type 2 diabetes mellitus: a systematic review and meta-analysis. Diabetes Metab J 2016;40:253-271.
    doi: 10.4093/dmj.2016.40.4.253pmc: PMC4995180pubmed: 27535644google scholar: lookup
  48. Pratt-Phillips SE, Owens KM, Dowler LE, Cloninger MT. Assessment of resting insulin and leptin concentrations and their association with managerial and innate factors in horses. J Equine Vet Sci 2010;30:127-133.
    doi: 10.1016/j.jevs.2010.01.060google scholar: lookup
  49. Suagee JK, Corl BA, Crisman MV, Pleasant RS, Thatcher CD, Geor RJ. Relationships between body condition score and plasma inflammatory cytokines, insulin, and lipids in a mixed population of light-breed horses. J Vet Intern Med 2013;27:157-163.
    doi: 10.1111/jvim.12021pubmed: 23216530google scholar: lookup
  50. Box JR, McGowan CM, Raekallio MR, Mykkänen AK, Carslake H, Karikoski NP. Insulin dysregulation in a population of Finnhorses and associated phenotypic markers of obesity. J Vet Intern Med 2020;34:1599-1605.
    doi: 10.1111/jvim.15782pmc: PMC7379004pubmed: 32557899google scholar: lookup
  51. Van Den Wollenberg L, Vandendriessche V, Van Maanen K, Counotte GHM. Comparison of two diagnostic methods to detect insulin dysregulation in horses under field conditions. J Equine Vet Sci 2020;88:102954.
    doi: 10.1016/j.jevs.2020.102954pubmed: 32303301google scholar: lookup
  52. Fitzgerald DM, Anderson ST, Sillence MN, De Laat MA. The cresty neck score is an independent predictor of insulin dysregulation in ponies. PLoS One 2019;14:e0220203.
    pmc: PMC6655749pubmed: 31339945
  53. Ragno VM, Klein CD, Sereda NS. Morphometric, metabolic, and inflammatory markers across a cohort of client-owned horses and ponies on the insulin dysregulation spectrum. J Equine Vet Sci 2021;105:103715.
    doi: 10.1016/j.jevs.2021.103715pubmed: 34607688google scholar: lookup
  54. Carter RA, Treiber KH, Geor RJ, Douglass L, Harris PA. Prediction of incipient pasture-associated laminitis from hyperinsulinaemia, hyperleptinaemia and generalised and localised obesity in a cohort of ponies. Equine Vet J 2009;41:171-178.
    doi: 10.2746/042516408X342975pubmed: 19418747google scholar: lookup
  55. De Laat MA, Sillence MN, Reiche DB. Phenotypic, hormonal, and clinical characteristics of equine endocrinopathic laminitis. J Vet Intern Med 2019;33:1456-1463.
    doi: 10.1111/jvim.15419pmc: PMC6524085pubmed: 30697823google scholar: lookup
  56. Li FI, Spence RJ, de Laat MA. Association between insulin dysregulation and adrenocorticotropic hormone in aged horses and ponies with no clinical signs of pituitary pars intermedia dysfunction. Equine Vet J 2023;55:1003-1011.
    doi: 10.1111/evj.13925pubmed: 36641787google scholar: lookup
  57. Galinelli NC, Bamford NJ, Erdody ML. Effect of pergolide treatment on insulin dysregulation in horses and ponies with pituitary pars intermedia dysfunction. Equine Vet J 2025;57:1612-1622.
    doi: 10.1111/evj.14468pmc: PMC12508286pubmed: 39967360google scholar: lookup

Citations

This article has been cited 0 times.
Subscribe to our newsletter
Join 99,005 horse owners like you who receive our email updates on horse health and nutrition.