How Endocrine Disorders Impact Equine Athletes

Endocrine disorders affect a large number of equids, with pituitary pars intermedia dysfunction (PPID) affecting 20% of horses older than 20 and equine metabolic syndrome (EMS)/insulin dysregulation (ID) affecting roughly 16% of ponies, with likely a similar percentage in horses (1,2). While traditionally the main concern with these conditions in our equine athletes has been the development of laminitis, concurrent disorders are becoming more clinically apparent (3). 

Joint and tendon issues associated with endocrine disorders have been identified in humans, and we are just starting to recognize them in horses as well. The similar pathophysiology between the two species lends itself to a One-Health approach (4). Other effects of endocrine disorders on equine athletes include suspensory ligament injury, obesity, exercise intolerance, insulin dysregulation, dyslipidemia, osteoarthritis, osteochondrosis, placental dysfunction, cardiac disease, and muscle atrophy.  

Endocrine Disorders’ Effects on the Musculoskeletal System 

The effects of endocrine disorders impact equine athletes in several ways, including:  

• Cushing’s in humans has been linked to Achilles tendon injury (5). Similarly, PPID has been linked to suspensory ligament disorders independent of age-related change (6). 

• Obesity and insulin resistance can cause a metabolic phenotype in humans and possibly horses (7). In humans with metabolic syndrome, their insulin and glucose dynamics are disrupted after intra-articular steroid injections (8), and we have seen similar insulin spikes post-steroid injections in even metabolically normal horses (9). Likewise, PPID horses have similar spikes to normal horses, and new data show ID horses have higher spikes than either normal or PPID horses. Horses don’t have the compensatory adiponectin mechanism that humans have in response to steroids, making them more at risk for laminitis. 

Endocrine Disorders and Other Body Systems 

Endocrine disease impacts many other body systems in addition to the musculoskeletal system. For example, PPID can affect the immune system, respiratory system, skin, and teeth. EMS/ID can affect adipose, the vasculature, and the reproductive system. Mare obesity/EMS/ID has effects on placental health and is associated with the development of osteochondrosis in their offspring (10). Diet and exercise play large roles in managing EMS/ID. Past medical therapies have included metformin and thyro-L, while current and future options informed by human medicine include supplements such as resveratrol and amino acids (11) and also SGLT2 inhibitors (12, 13, 14). 

While diagnosis in the past was based on clinical signs and a high baseline fasted insulin or ACTH concentration, current, more sensitive dynamic tests evaluate responses to either oral (Karo Syrup, oral sugar test to assess for EMS/ID) or TRH stimulation (ACTH pre- and 10 minutes post-injection to assess for PPID) so we don’t miss subclinical cases. In conclusion, early identification and proper management of equine endocrine disease can improve the health and welfare of our performance horses. 

References 

1. Al-Ansari AS, Golding E, Walshe N, Mooney CT, Duggan V. Obesity and obesity-associated metabolic disease conditions in Connemara ponies in Ireland. Equine Vet J. 2023 Nov 20. doi: 10.1111/evj.14029. Epub ahead of print. PMID: 37985219.2 

2. Ireland JL, McGowan CM. Epidemiology of pituitary pars intermedia dysfunction: A systematic literature review of clinical presentation, disease prevalence and risk factors. Vet J. 2018 May;235:22-33. doi: 10.1016/j.tvjl.2018.03.002. Epub 2018 Mar 8. PMID: 29704935. 

3. Manfredi JM, Jacob S, Norton E. A one-health lens offers new perspectives on the importance of endocrine disorders in the equine athlete. J Am Vet Med Assoc. 2023 Jan 2;261(2):153-164. doi: 10.2460/javma.22.11.0485. PMID: 36595370. 

4. Manfredi JM, Jacob SI, Boger BL, Norton EM. A one-health approach to identifying and mitigating the impact of endocrine disorders on human and equine athletes. Am J Vet Res. 2022 Dec 27;84(2):ajvr.22.11.0194. doi: 10.2460/ajvr.22.11.0194. PMID: 36563063. 

5. Batisse M, Somda F, Delorme JP, Desbiez F, Thieblot P, Tauveron I. Spontaneous rupture of Achilles tendon and Cushing’s disease. Case report. Ann Endocrinol (Paris). 2008 Dec;69(6):530-1. doi: 10.1016/j.ando.2008.06.003. Epub 2008 Sep 6. PMID: 18774551. 

6. Hofberger S, Gauff F, Licka T. Suspensory ligament degeneration associated with pituitary pars intermedia dysfunction in horses. Vet J. 2015 Mar;203(3):348-50. doi: 1016/j.tvjl.2014.12.037. Epub 2015 Jan 6. PMID: 25641552. 

7. Sampath SJP, Venkatesan V, Ghosh S, Kotikalapudi N. Obesity, Metabolic Syndrome, and Osteoarthritis-An Updated Review. Curr Obes Rep. 2023 Sep;12(3):308-331. doi: 10.1007/s13679-023-00520-5. Epub 2023 Aug 14. PMID: 37578613. 

8. Choudhry MN, Malik RA, Charalambous CP. Blood Glucose Levels Following Intra-Articular Steroid Injections in Patients with Diabetes: A Systematic Review. JBJS Rev. 2016 Mar 22;4(3):e5. doi: 10.2106/JBJS.RVW.O.00029. PMID: 27500431. 

9. Boger BL, Manfredi JM, Loucks AR, Salamey MZ, Kapeller LE, Fricano AG, Winkler A, Yob C, Colbath AC. Intra-articular triamcinolone acetonide injection results in increases in systemic insulin and glucose concentrations in horses without insulin dysregulation. Equine Vet J. 2023 Sep 13. doi: 10.1111/evj.14003. Epub ahead of print. PMID: 37705233 

10. Robles M, Nouveau E, Gautier C, Mendoza L, Dubois C, Dahirel M, Lagofun B, Aubrière MC, Lejeune JP, Caudron I, Guenon I, Viguié C, Wimel L, Bouraima-Lelong H, Serteyn D, Couturier-Tarrade A, Chavatte-Palmer P. Maternal obesity increases insulin resistance, low-grade inflammation and osteochondrosis lesions in foals and yearlings until 18 months of age. PLOS One. 2018 Jan 26;13(1):e0190309. doi: 10.1371/journal.pone.0190309. PMID: 29373573; PMCID: PMC5786290. 

11. Manfredi JM, Stapley ED, Nadeau JA, Nash D. Investigation of the Effects of a Dietary Supplement on Insulin and Adipokine Concentrations in Equine Metabolic Syndrome/Insulin Dysregulation. J Equine Vet Sci. 2020 May;88:102930. doi: 10.1016/j.jevs.2020.102930. Epub 2020 Jan 22. PMID: 32303322. 

12. Kellon EM, Gustafson KM. Use of the SGLT2 inhibitor canagliflozin for control of refractory equine hyperinsulinemia and laminitis. Open Vet J. 2022 Jul-Aug;12(4):511-518. doi: 10.5455/OVJ.2022.v12.i4.14. Epub 2022 Aug 7. PMID: 36118716; PMCID: PMC9473365. 

13. Meier A, Reiche D, de Laat M, Pollitt C, Walsh D, Sillence M. The sodium-glucose co-transporter 2 inhibitor velagliflozin reduces hyperinsulinemia and prevents laminitis in insulin-dysregulated ponies. PLoS One. 2018 Sep 13;13(9):e0203655. doi: 10.1371/journal.pone.0203655. PMID: 30212530; PMCID: PMC6136744. 

14. Lindåse S, Nostell K, Forslund A, Bergsten P, Bröjer J. Short-term effects of canagliflozin on glucose and insulin responses in insulin dysregulated horses: A randomized, placebo-controlled, double-blind, study. J Vet Intern Med. 2023 Nov-Dec;37(6):2520-2528. doi: 10.1111/jvim.16906. Epub 2023 Oct 21. PMID: 37864426; PMCID: PMC10658518. 

About Dr. Jane Manfredi 

Jane Manfredi, DVM, MS, PhD, DACVS-LA, DACVSMR (Equine), PGDIP Vet Med Ed, is the Mary Anne McPhail Dressage Chair in Equine Sports Medicine and an associate professor in the Department of Large Animal Clinical Sciences at Michigan State University’s College of Veterinary Medicine, in East Lansing. Additionally, she graduated from the Atlantic Veterinary College, in Prince Edward Island, Canada, did an internship at Mississippi State University, in Starkville, and spent time in a private mixed large animal private practice and at two Chicago racetracks before completing a large animal surgical residency at the University of Minnesota, in Saint Paul. 

Dr. Manfredi completed a PhD at Michigan State in Comparative Medicine and Integrative Biology and became boarded in equine sports medicine and rehabilitation before joining the faculty. Her research interests include the intersection of endocrine disorders and osteoarthritis, sports medicine and rehabilitation of the performance horse, and rider/horse/tack interactions. She has a passion for teaching and has been awarded the MSU Teacher Scholar Award as well as being named an Academy of Veterinary Educators Distinguished Expert. Additionally, Dr. Manfredi is an FEI-level dressage rider. 

Related Reading

• Effects of Pasture and Obesity on ID and Adiponectin in Horses
• Equine Endocrinopathies: Is it ID, PPID, or Both?
• How to Feed Horses Prone to Endocrinopathic Laminitis

Stay in the know! Sign up for EquiManagement’s FREE weekly newsletters to get the latest equine research, disease alerts, and vet practice updates delivered straight to your inbox.