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Bertin FR, Frank N, Breuhaus BA, Schott HC, Kritchevsky JE. Diagnosis and management of thyroid disorders and thyroid hormone supplementation in adult horses and foals. Equine Vet J 2024; 56:243-252. [PMID: 37533378 DOI: 10.1111/evj.13981] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2023] [Accepted: 07/13/2023] [Indexed: 08/04/2023]
Abstract
Equine thyroid disorders pose a diagnostic challenge in clinical practice because of the effects of nonthyroidal factors on the hypothalamic-pituitary-thyroid axis, and the horse's ability to tolerate wide fluctuations in thyroid hormone concentrations and survive without a thyroid gland. While benign thyroid tumours are common in older horses, other disorders like primary hypothyroidism or hyperthyroidism in adult horses and congenital hypothyroidism in foals are rare. There is a common misunderstanding regarding hypothyroidism in adult horses, especially when associated with the clinical profile of obesity, lethargy, and poor performance observed in dogs and humans. Low blood thyroid hormone concentrations are often detected in horses as a secondary response to metabolic and disease states, including with the nonthyroidal illness syndrome; however, it is important to note that low thyroid hormone concentrations in these cases do not necessarily indicate hypothyroidism. Assessing equine thyroid function involves measuring thyroid hormone concentrations, including total and free fractions of thyroxine (T4) and triiodothyronine (T3); however, interpreting these results can be challenging due to the pulsatile secretion of thyroid hormones and the many factors that can affect their concentrations. Dynamic testing, such as the thyrotropin-releasing hormone stimulation test, can help assess the thyroid gland response to stimulation. Although true hypothyroidism is extremely rare, thyroid hormone supplementation is commonly used in equine practice to help manage obesity and poor performance. This review focuses on thyroid gland pathophysiology in adult horses and foals, interpretation of blood thyroid hormone concentrations, and evaluation of horses with thyroid disorders. It also discusses the use of T4 supplementation in equine practice.
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Affiliation(s)
- François-René Bertin
- School of Veterinary Science at The University of Queensland, UQ Gatton Campus, Gatton, Queensland, Australia
| | - Nicholas Frank
- College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi, USA
| | - Babetta A Breuhaus
- College of Veterinary Medicine at North Caroline State University, Raleigh, North Carolina, USA
| | - Harold C Schott
- College of Veterinary Medicine at Michigan State University, East Lansing, Michigan, USA
| | - Janice E Kritchevsky
- College of Veterinary Medicine at Purdue University, West Lafayette, Indiana, USA
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Moss A, Leise B, Hackett E. Stress response as a contributing factor in horses with laminitis. J Vet Sci 2023; 24:e33. [PMID: 37012040 PMCID: PMC10071284 DOI: 10.4142/jvs.22039] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Revised: 01/31/2023] [Accepted: 02/03/2023] [Indexed: 03/16/2023] Open
Abstract
BACKGROUND Laminitis is a complex and debilitating disease of horses. Numerous predisposing factors contribute to laminitis development, however the exact pathogenesis remains undetermined. Serum T4, cortisol, and histamine are components of the innate stress response and could play a causative or contributory role. Stress hormone concentrations in laminitis are largely unknown. OBJECTIVE To evaluate parameters associated with stress response in horses with laminitis, and compare these to healthy horses and horses with gastrointestinal (GI) disease. METHODS Thirty-eight adult horses presenting for non-medical conditions, GI abnormalities, or clinical laminitis were prospectively enrolled. Horses were assigned to the appropriate disease group (healthy, GI disease, and laminitis) and had blood drawn on presentation to the hospital. Samples were analyzed for plasma endogenous adrenocorticotrophic hormone (eACTH), serum cortisol, serum thyroid hormone, and plasma histamine. RESULTS Stress hormone concentrations were significantly different between horses in the laminitis and GI disease groups. Plasma histamine levels were highest in horses with laminitis, compared with GI disease and controls. Both horses with laminitis and GI disease had increased plasma eACTH when compared to healthy horses. Horses with GI disease had higher serum cortisol concentrations than horses with laminitis or controls. Serum T4 was lower in horses with GI disease than in horses with laminitis and controls. CONCLUSIONS Horses with laminitis had relative increases in both plasma histamine and eACTH concentrations. Serum T4 and cortisol concentrations of horses with laminitis did not differ significantly when compared to healthy horses. The role of stress hormones in equine disease warrants further investigation.
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Affiliation(s)
- Alexandra Moss
- Department of Clinical Sciences, Colorado State University, Fort Collins, CO 80523, USA
| | - Britta Leise
- School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA
| | - Eileen Hackett
- Department of Clinical Sciences, Colorado State University, Fort Collins, CO 80523, USA
- Department of Clinical Sciences, Cornell University, Ithaca, NY 14853, USA
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Pasternak JA, MacPhee DJ, Lunney JK, Rowland RRR, Dyck MK, Fortin F, Dekkers JCM, Plastow GS, Harding JCS. Thyroid hormone suppression in feeder pigs following polymicrobial or porcine reproductive and respiratory syndrome virus-2 challenge. J Anim Sci 2021; 99:6420436. [PMID: 34734242 DOI: 10.1093/jas/skab325] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Accepted: 11/01/2021] [Indexed: 01/18/2023] Open
Abstract
Thyroid hormones are powerful regulators of growth, development, and basal metabolic rate and can be dysregulated under conditions of severe stress or illness. To understand the role of these hormones in porcine disease response, serum samples were obtained from three batches of nursery-aged pigs (n = 208) exposed to a natural polymicrobial disease challenge with an array of bacterial and viral pathogens. Levels of total thyroxin (T4) and triiodothyronine (T3) assessed in sera by radioimmunoassay, decreased significantly by 14 days post-exposure (DPE). Levels of T3 partially rebounded by 48 DPE, while T4 levels remain depressed. Post-exposure T3 and T4 levels were positively correlated with acute and long-term average daily gain (ADG). Cross-sectional sampling of animals maintained at the high health source farms, showed no equivalent change in either hormone when managed under standard industrial conditions. To further elucidate the effect of porcine reproductive and respiratory syndrome virus (PRRSV)-infection on thyroid hormone levels, archived sera over 42 days post inoculation (DPI) from nursery pigs (N = 190) challenged with one of two PRRSV2 strains by the PRRS Host Genetics Consortium were similarly assessed, with animals selected in a two-by-two design, to investigate biological extremes in ADG and viral load (VL). All animals showed a similar decrease in both thyroid hormones reaching a minimum at 7 DPI and returning to near pre-challenge levels by 42 DPI. Post-challenge T3 and T4 levels were significantly greater in high ADG groups, with no significant association with VL or strain. The results of this study demonstrate porcine susceptibility to thyroid disruption in response to disease challenge and demonstrate a relationship between this response and growth performance.
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Affiliation(s)
- J Alex Pasternak
- Department of Animal Sciences, Purdue University, West Lafayette, IN 47907, USA
| | - Daniel J MacPhee
- Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada
| | | | - Raymond R R Rowland
- College of Veterinary Medicine, University of Illinois, Urbana, IL 61802, USA
| | - Michael K Dyck
- Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB T6G 2R3, Canada
| | - Frédéric Fortin
- Centre de développement du porc du Québec Inc., Québec City, QC G1V 4M6, Canada
| | - Jack C M Dekkers
- Department of Animal Science, Iowa State University, Ames, IA 50011, USA
| | - Graham S Plastow
- Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB T6G 2R3, Canada
| | - John C S Harding
- Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada
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Gehlen H, Jaburg N, Merle R, Winter J. Can Endocrine Dysfunction Be Reliably Tested in Aged Horses That Are Experiencing Pain? Animals (Basel) 2020; 10:ani10081426. [PMID: 32824027 PMCID: PMC7459856 DOI: 10.3390/ani10081426] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Revised: 08/09/2020] [Accepted: 08/11/2020] [Indexed: 01/18/2023] Open
Abstract
Simple Summary Pituitary pars intermedia dysfunction (PPID) is an endocrine (secreting internally) disease of aged horses and ponies. An enlargement (hyperplasia) of the pars intermedia of the pituitary gland leads to an increased secretion of hormones, including adrenocorticotropic hormone (ACTH). The main tests for a diagnosis of PPID are the measurement of basal ACTH and the thyrotropin-releasing hormone (TRH) stimulation test, where TRH stimulates the secretion of ACTH. Since pain can also lead to elevated concentrations of ACTH, it is unclear whether horses with pain can be tested for PPID correctly. The aim of the present study was to find out whether pain caused a marked increase of ACTH can lead to a false positive result in the diagnosis of PPID. Therefore, we examined fifteen horses treated for different pain conditions, which also served as their own controls as soon as they were pain-free again. The ACTH and cortisol were measured before and after the TRH stimulation test. There was no significant difference in the ACTH concentration in horses with pain and the controls, between different pain intensities or between disease groups. Thus, measuring the basal ACTH concentration and performing the TRH stimulation test for the diagnosis of PPID seem to be possible in horses with a treated low to moderate pain condition. Abstract The aim of the present study was to evaluate (i) the effects of different intensities and types of treated pain on the basal concentrations of adrenocorticotropic hormone (ACTH) and cortisol, and (ii) the thyrotropin-releasing hormone (TRH) stimulation test, to determine whether treated pain caused a marked increase of ACTH, which would lead to a false positive result in the diagnosis of pituitary pars intermedia dysfunction (PPID). Methods: Fifteen horses with treated low to moderate pain intensities were part of the study. They served as their own controls as soon as they were pain-free again. The horses were divided into three disease groups, depending on their underlying disease (disease group 1 = colic, disease group 2 = laminitis, disease group 3 = orthopedic problems). A composite pain scale was used to evaluate the intensity of the pain. This pain scale contained a general part and specific criteria for every disease. Subsequently, ACTH and cortisol were measured before and after the intravenous application of 1 mg of TRH. Results: There was no significant difference in the basal or stimulated ACTH concentration in horses with pain and controls, between different pain intensities or between disease groups. Descriptive statistics, however, revealed that pain might decrease the effect of TRH on the secretion of ACTH. There was an increase of ACTH 30 min after TRH application (p = 0.007) in the treated pain group, but this difference could not be statistically confirmed. Measuring the basal ACTH concentration and performing the TRH stimulation test for the diagnosis of PPID seem to be possible in horses with low to moderate pain.
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Affiliation(s)
- Heidrun Gehlen
- Equine Clinic, Freie University of Berlin, 14163 Berlin, Germany; (N.J.); (J.W.)
- Correspondence:
| | - Nina Jaburg
- Equine Clinic, Freie University of Berlin, 14163 Berlin, Germany; (N.J.); (J.W.)
| | - Roswitha Merle
- Veterinary Department, Institute of Veterinary Epidemiology, Freie University Berlin, 14163 Berlin, Germany;
| | - Judith Winter
- Equine Clinic, Freie University of Berlin, 14163 Berlin, Germany; (N.J.); (J.W.)
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Costello J, Firshman AM, Brown JC, Maher M, Tadros EM. Response to thyrotropin-releasing hormone (TRH) in a horse with hyperthyroidism associated with a functional thyroid adenoma. THE CANADIAN VETERINARY JOURNAL = LA REVUE VETERINAIRE CANADIENNE 2019; 60:1189-1193. [PMID: 31692666 PMCID: PMC6805031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
A 16-year-old American Paint Horse gelding was presented for evaluation of weight loss and high serum thyroid hormone concentrations resulting from a functional thyroid adenoma. The horse showed no response to a thyrotropin-releasing hormone (TRH) stimulation test. Clinical signs resolved following surgical removal of the adenoma.
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Affiliation(s)
- Jillian Costello
- Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, 1365 Gortner Avenue, Saint Paul, Minnesota 55108, USA (Costello, Firshman, Brown, Maher); Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, 4125 Beaumont Road Lansing, Michigan 48910, USA (Tadros)
| | - Anna M Firshman
- Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, 1365 Gortner Avenue, Saint Paul, Minnesota 55108, USA (Costello, Firshman, Brown, Maher); Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, 4125 Beaumont Road Lansing, Michigan 48910, USA (Tadros)
| | - Jennifer C Brown
- Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, 1365 Gortner Avenue, Saint Paul, Minnesota 55108, USA (Costello, Firshman, Brown, Maher); Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, 4125 Beaumont Road Lansing, Michigan 48910, USA (Tadros)
| | - Michael Maher
- Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, 1365 Gortner Avenue, Saint Paul, Minnesota 55108, USA (Costello, Firshman, Brown, Maher); Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, 4125 Beaumont Road Lansing, Michigan 48910, USA (Tadros)
| | - Elizabeth M Tadros
- Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, 1365 Gortner Avenue, Saint Paul, Minnesota 55108, USA (Costello, Firshman, Brown, Maher); Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, 4125 Beaumont Road Lansing, Michigan 48910, USA (Tadros)
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Bertin FR, Eichstadt Forsythe L, Kritchevsky JE. Effects of high doses of levothyroxine sodium on serum concentrations of triiodothyronine and thyroxine in horses. Am J Vet Res 2019; 80:565-571. [DOI: 10.2460/ajvr.80.6.565] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Breuhaus BA. Thyroid Hormone and Thyrotropin Concentrations and Responses to Thyrotropin-Stimulating Hormone in Horses with PPID Compared with Age-Matched Normal Horses. J Equine Vet Sci 2019; 75:35-40. [PMID: 31002090 DOI: 10.1016/j.jevs.2019.01.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Revised: 12/31/2018] [Accepted: 01/14/2019] [Indexed: 12/01/2022]
Abstract
Glucocorticoids are known to exert inhibitory action on the hypothalamic-pituitary-thyroid axis. With recent evidence that free plasma cortisol and urinary excretion of cortisol metabolites may be increased in horses with pituitary pars intermedia dysfunction (PPID), it is important to further examine thyroid function in horses with PPID. To test the hypothesis that serum thyrotropin (TSH) concentrations are decreased in horses with PPID, baseline serum thyroid hormone and TSH concentrations, and responses to TSH-releasing hormone (TRH), were compared between 12 horses diagnosed as having PPID and 14 age-matched normal horses. Horses with PPID had resting serum concentrations of free thyroxine by equilibrium dialysis (fT4D) and TSH that were significantly lower than serum concentrations of fT4D and TSH in age-matched normal horses. Serum concentrations of total T4 and total and free triiodothyronine (T3) were also lower in horses with PPID compared with normal horses, but the differences did not reach statistical significance. Thyroid hormone and TSH responses to TRH administration were not different between horses with PPID and normal horses. In conclusion, serum fT4D concentrations are decreased in horses with PPID without an appropriate increase in serum TSH concentrations. Normal serum thyroid hormone and TSH concentration responses to exogenous TRH administration support the theory that increased glucocorticoid activity in horses with PPID may exert prolonged tonic suppression, but not complete inhibition, of TRH and subsequent TSH release, similar to what has been observed in other species.
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Affiliation(s)
- Babetta A Breuhaus
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, 1060 William Moore Drive, Raleigh, NC.
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Breuhaus BA. Serum Thyroid Hormone and Thyrotropin Concentrations in Adult Horses as They Age. J Equine Vet Sci 2018; 68:21-25. [PMID: 31256883 DOI: 10.1016/j.jevs.2018.04.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Revised: 04/21/2018] [Accepted: 04/23/2018] [Indexed: 10/17/2022]
Abstract
With more horses remaining active longer in life, it is important to characterize changes that occur normally with aging, so that these can be differentiated from development of disease. The objective of the study was to test the hypotheses that geriatric horses have lower circulating concentrations of thyroid hormones and/or higher serum thyrotropin (TSH) concentrations compared to younger horses. Serum thyroid hormone and TSH concentrations from 71 normal, healthy horses that had participated in prior research projects were analyzed for effects of age, sex, and season when samples were obtained. All samples had been assayed in the same previously validated radioimmunoassays. There were no differences in serum concentrations of thyroid hormones or TSH by sex or season. Serum total thyroxine (T4) was greater in 3- to 6-year-old horses compared to all other age groups and was negatively correlated with age. There were no differences among age groups for free T4 and total and free tri-iodothyronine (T3). Serum TSH concentration was significantly greater in old horses (≥15 or ≥20 years) compared to young (3-10 years) and intermediate (11-14 years) age groups. Serum TSH was positively correlated with age. There were no significant differences in thyroid hormone responses to thyrotropin releasing hormone (TRH) among young, intermediate, or old horses. However, the TSH response to TRH was significantly different in both groups of older horses compared to intermediate and young horses. Serum total thyroxine concentrations decrease and serum TSH concentrations increase in horses as they age, with no changes in free T4 or T3.
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Affiliation(s)
- Babetta A Breuhaus
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC.
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Lester SJ, Mollat WH, Bryant JE. Overview of Clinical Pathology and the Horse. Vet Clin North Am Equine Pract 2015. [DOI: 10.1016/j.cveq.2015.04.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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Breuhaus BA. Thyroid function and dysfunction in term and premature equine neonates. J Vet Intern Med 2014; 28:1301-9. [PMID: 24934827 PMCID: PMC4857961 DOI: 10.1111/jvim.12382] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 03/27/2014] [Accepted: 04/23/2014] [Indexed: 11/28/2022] Open
Abstract
Background This study was performed to compare thyroid function of premature foals to term foals. Hypothesis Premature foals are more markedly hypothyroxinemic than expected for their severity of illness alone. Animals Twenty clinically normal term foals; 28 sick, hospitalized term foals; 24 sick, hospitalized premature foals. Methods Thyroid hormones (TH) and thyrotropin (TSH) were measured, both at rest and in response to thyrotropin‐releasing hormone (TRH), in the 3 groups of foals. Clinical and clinicopathologic data were recorded. Results Normal foals had high TH at birth, which decreased over the first month into the normal reference range for adult horses. TSH was within the normal adult reference range soon after birth, and did not change over time. At 24–36 hours of age, triiodothyronine (T3) was significantly lower in both premature and term hospitalized foals compared to normal foals; premature foals were not different from term hospitalized foals. Thyroxine (T4) was not different between normal and term hospitalized foals, but was significantly lower than in premature foals of both of these groups. TSH was not different among the 3 groups. TRH stimulation tests identified significant differences in T4 among all 3 groups of foals, whereas T3 was similar in premature and term hospitalized foals and different from normal foals. TSH response to TRH was significantly higher in premature foals compared to normal foals. Conclusions and Clinical Importance The hypothalamic‐pituitary‐thyroid axis is different in foals compared to adult horses. Sick foals exhibit nonthyroidal illness syndrome. Premature foals are more markedly hypothyroxinemic than can be accounted for by their severity of illness alone.
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Affiliation(s)
- B A Breuhaus
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC
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