Effect of dietary carbohydrates and time of year on ACTH and cortisol concentrations in adult and aged horses.
Abstract: Diagnosis of equine pituitary pars intermedia dysfunction (PPID) remains a challenge as multiple factors (stress, exercise, and time of year) influence ACTH and cortisol concentrations. To assess endocrine status in a study designed to evaluate the effects of age and diet on glucose and insulin dynamics, we performed thyrotropin-releasing hormone (TRH) stimulation tests and overnight dexamethasone suppression tests in March, May, August, and October on 16 healthy Thoroughbred and Standardbred mares and geldings. Horses were grouped by age: adult (mean ± SD; 8.8 ± 2.9 yr; n = 8) and aged (20.6 ± 2.1 yr; n = 8). None of the horses showed clinical signs (hypertrichosis, regional adiposity, skeletal muscle atrophy, lethargy) of pituitary pars intermedia dysfunction. Horses were randomly assigned to groups of 4, blocked for age, and fed grass hay plus 4 isocaloric concentrate diets (control, starch-rich, fiber-rich, and sugar-rich) using a balanced Latin square design. Data were analyzed using a multivariable linear mixed regression model. Baseline ACTH was significantly higher in aged horses (mean ± standard error of the mean; 60.0 ± 10.7 pg/mL) adapted to the starch-rich diet compared to adult horses (15.7 ± 12.0 pg/mL) on the same diet (P = 0.017). After controlling for age and diet, baseline ACTH concentrations were significantly increased in October (57.7 ± 7.1 pg/mL) compared to March (13.2 ± 7.1 pg/mL; P < 0.001), May (12.4 ± 7.1 pg/mL; P < 0.001), and August (24.2 ± 7.1 pg/mL; P < 0.001), whereas post-TRH ACTH was higher in August (376.6 ± 57.6 pg/mL) and October (370.9 ± 57.5 pg/mL) compared to March (101.9 ± 57.3 pg/mL; P < 0.001) and May (74.5 ± 57.1 pg/mL; P < 0.001). Aged horses had significantly higher post-dexamethasone cortisol on the starch-rich diet (0.6 ± 0.1 μg/dL) compared to the sugar-rich diet (0.2 ± 0.1 μg/dL; P = 0.021). Post-dexamethasone cortisol was significantly higher in October (0.6 ± 0.1 μg/dL) compared to March (0.3 ± 0.1 μg/dL; P = 0.005), May (0.2 ± 0.1 μg/dL; P < 0.001), and August (0.3 ± 0.1 μg/dL; P = 0.004). Breed did not influence ACTH or cortisol measurements. In conclusion, in addition to age and time of year, diet is a potential confounder as animals on a starch-rich diet may be incorrectly diagnosed with pituitary pars intermedia dysfunction.
Copyright © 2017 Elsevier Inc. All rights reserved.
Publication Date: 2017-11-01 PubMed ID: 29195115DOI: 10.1016/j.domaniend.2017.10.005Google Scholar: Lookup
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- Journal Article
- Randomized Controlled Trial
- Research Support
- Non-U.S. Gov't
- Adrenocorticotropic Hormone (ACTH)
- Adult Horses
- Age Factors
- Carbohydrates
- Cortisol
- Diagnostic Technique
- Dietary Supplements
- Endocrine System
- Equine Diseases
- Equine Health
- Geriatric Horses
- Glucose
- Horses
- Insulin
- Pituitary Pars Intermedia Dysfunction
- Seasonal Variation
- Standardbred Horses
- Stress
- Thoroughbreds
- Veterinary Medicine
Summary
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This study examines the effect of diet and different times of the year on levels of ACTH and cortisol in adult and older horses, and how this might influence diagnoses of equine pituitary pars intermedia dysfunction (PPID). Results suggest that age, time of year, and diet, particularly a starch-rich diet, all influence these hormone levels and could potentially result in misdiagnoses of this equine condition.
Objective and Design of the Research
- The research aimed to investigate how dietary carbohydrates, age, and different periods of the year would affect ACTH (adrenocorticotropic hormone) and cortisol levels in horses.
- This influence has implications for diagnosing equine pituitary pars intermedia dysfunction (PPID), a condition better understood through the study of these hormones.
- The researchers used both thyrotropin-releasing hormone (TRH) stimulation and overnight dexamethasone suppression tests at several yearly intervals on 16 Thoroughbred and Standardbred healthy horses.
- Horses were grouped by age into adult and aged categories and assigned to four dietary groups consisting of control, starch-rich, fiber-rich, and sugar-rich diets. This was done using a balanced Latin square design.
Key Results
- Baseline ACTH was found to be significantly higher in older horses adapted to a starch-rich diet compared to the adult horses on the same diet.
- ACTH levels were significantly elevated in October compared to other times of the year, while post-TRH ACTH levels were higher in August and October compared to March and May,
- Older horses on a starch-rich diet had significantly higher post-dexamethasone cortisol levels compared to when they were on a sugar-rich diet.
- Post-dexamethasone cortisol levels were found to be significantly elevated in October compared to March, May, and August.
- The breed of the horse did not appear to influence either ACTH or cortisol measurements.
Conclusion
- Results suggest that the diagnosis of pituitary pars intermedia dysfunction in horses can potentially be affected by age, time of year, and diet. Specifically, a starch-rich diet may lead to incorrect diagnoses due to its influence on ACTH and cortisol levels.
Cite This Article
APA
Jacob SI, Geor RJ, Weber PSD, Harris PA, McCue ME.
(2017).
Effect of dietary carbohydrates and time of year on ACTH and cortisol concentrations in adult and aged horses.
Domest Anim Endocrinol, 63, 15-22.
https://doi.org/10.1016/j.domaniend.2017.10.005 Publication
Researcher Affiliations
- Michigan State University College of Veterinary Medicine, 736 Wilson Road, East Lansing, MI 48824, USA. Electronic address: jacobs67@msu.edu.
- Massey University College of Sciences, Private Bag 11222, Palmerston North 4442, New Zealand.
- Michigan State University College of Veterinary Medicine, 736 Wilson Road, East Lansing, MI 48824, USA.
- Equine Studies Group, WALTHAM Centre for Pet Nutrition, Freeby Lane, Leicestershire, UK.
- University of Minnesota College of Veterinary Medicine, 1365 Gortner Avenue, St. Paul, MN 55108, USA.
MeSH Terms
- Adrenocorticotropic Hormone / blood
- Adrenocorticotropic Hormone / metabolism
- Aging / physiology
- Animal Feed / analysis
- Animals
- Diet / veterinary
- Dietary Carbohydrates
- Female
- Horses / blood
- Horses / physiology
- Hydrocortisone / blood
- Hydrocortisone / metabolism
- Male
- Pituitary Gland, Intermediate / drug effects
- Pituitary Gland, Intermediate / physiology
- Seasons
Citations
This article has been cited 13 times.- Holtby AR, McGivney BA, Browne JA, Katz LM, Murphy KJ, Hill EW. Variation in salivary cortisol responses in yearling Thoroughbred racehorses during their first year of training. PLoS One 2023;18(4):e0284102.
- Drozdzewska K, Gehlen H. Markers for internal neoplasia in the horse. Vet Med Sci 2023 Jan;9(1):132-143.
- Kirkwood NC, Hughes KJ, Stewart AJ. Prospective Case Series of Clinical Signs and Adrenocorticotrophin (ACTH) Concentrations in Seven Horses Transitioning to Pituitary Pars Intermedia Dysfunction (PPID). Vet Sci 2022 Oct 17;9(10).
- Kirkwood NC, Hughes KJ, Stewart AJ. Pituitary Pars Intermedia Dysfunction (PPID) in Horses. Vet Sci 2022 Oct 10;9(10).
- Thane K, Uricchio C, Frank N. Effect of early or late blood sampling on thyrotropin releasing hormone stimulation test results in horses. J Vet Intern Med 2022 Mar;36(2):770-777.
- 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 Sep;54(5):905-913.
- Kam YN, McKenzie K, Coyle M, Bertin FR. Repeatability of a thyrotropin-releasing hormone stimulation test for diagnosis of pituitary pars intermedia dysfunction in mature horses. J Vet Intern Med 2021 Nov;35(6):2885-2890.
- 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 (Basel) 2021 Mar 20;11(3).
- Satué K, Fazio E, Muñoz A, Medica P. Endocrine and Electrolyte Balances during Periovulatory Period in Cycling Mares. Animals (Basel) 2021 Feb 17;11(2).
- Horn R, Stewart AJ, Jackson KV, Dryburgh EL, Medina-Torres CE, Bertin FR. 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 Jan;35(1):560-570.
- Gardela J, Carbajal A, Tallo-Parra O, Olvera-Maneu S, Álvarez-Rodríguez M, Jose-Cunilleras E, López-Béjar M. Temporary Relocation during Rest Periods: Relocation Stress and Other Factors Influence Hair Cortisol Concentrations in Horses. Animals (Basel) 2020 Apr 8;10(4).
- 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 Mar-Apr;39(2):e70047.
- Galinelli NC, Bamford NJ, Erdody ML, Mackenzie SA, Warnken T, Harris PA, Sillence MN, Bailey SR. Effect of pergolide treatment on insulin dysregulation in horses and ponies with pituitary pars intermedia dysfunction. Equine Vet J 2025 Nov;57(6):1612-1622.
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