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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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Fazio E, Lindner A, Cravana C, Wegener J, Medica P, Hart-Mann U, Ferlazzo A. Effects of standardized exercise tests on plasma thyroid hormones' kinetics in Standardbred racehorses. J Equine Vet Sci 2021; 110:103853. [PMID: 34968655 DOI: 10.1016/j.jevs.2021.103853] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 12/17/2021] [Accepted: 12/20/2021] [Indexed: 11/26/2022]
Abstract
This study examined how a standard exercise test (SET) affected (1) thyroid hormones (THs) of horses and (2) the relationship between the VLa4 of horses and TH responses to the exercise in trained Standardbred racehorses (VLa4 is the velocity run at defined conditions at which a blood lactate concentration of 4 mmol/L is determined). 12 trained Standardbred racehorses (six stallions and six mares) performed SETs until the horses' blood lactate concentration was at or above 4 mmol/L. The horses were divided into three age groups (2, 3 and 4 years old); each group consists of 4 horses respectively (2 male and 2 female), to evaluate the effects of age and sex on hormonal responses to SET. During each SET, blood samples were taken at rest and after each interval and at the end of SET. Blood was analysed for total and free triiodothyronine (T3, fT3) as well as total and free thyroxine (T4, fT4). The statistical model included three fixed factors (SET, sex and age) and their main interactions. ANOVA analysis revealed that T3 and fT3 were significantly influenced by SETs. Plasma T3 and fT3 concentrations were higher in 4-year-old horses compared to the other age groups. All plasma THs concentrations were higher in mares than in stallions. Correlations revealed that a higher VLa4 was negatively related to all THs responses in 2-year-old Standardbred mares only. The SET used to determine VLa4 increased selected THs (T3, fT3); these increases were inversely related to VLa4 and affected by age and sex of the horses. The correlation of VLa4 with thyroid exercise' response might provide some additional information for performance evaluation of Standardbred racehorses, especially for evaluating training adaptation, according to sex and age. Further studies are necessary to provide support on the value of measuring THs in Standardbred racehorses of different sex and age.
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Affiliation(s)
- Esterina Fazio
- Department of Veterinary Sciences, Veterinary Physiology Unit, Polo Universitario Annunziata, Viale Palatucci 13, 98168 Messina, Italy
| | | | - Cristina Cravana
- Department of Veterinary Sciences, Veterinary Physiology Unit, Polo Universitario Annunziata, Viale Palatucci 13, 98168 Messina, Italy
| | | | - Pietro Medica
- Department of Veterinary Sciences, Veterinary Physiology Unit, Polo Universitario Annunziata, Viale Palatucci 13, 98168 Messina, Italy.
| | - Ulrich Hart-Mann
- Institute of Movement and Training Science; Faculty of Sport Science, 04109 Leipzig, Germany
| | - Adriana Ferlazzo
- Department of Veterinary Sciences, Veterinary Physiology Unit, Polo Universitario Annunziata, Viale Palatucci 13, 98168 Messina, Italy
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Kritchevsky J, Olave C, Tinkler S, Tropf M, Ivester K, Forsythe L, Couetil L. A randomised, controlled trial to determine the effect of levothyroxine on Standardbred racehorses. Equine Vet J 2021; 54:584-591. [PMID: 34101895 DOI: 10.1111/evj.13480] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Revised: 04/19/2021] [Accepted: 05/27/2021] [Indexed: 02/02/2023]
Abstract
BACKGROUND The use of thyroid supplement is pervasive in athletic horses although its effects on measures of performance are not known. OBJECTIVES One purpose of this study was to determine whether supra-physiologic doses of levothyroxine affect the velocities at which blood lactate was greater than 4 mmol/L (VLa4 ) and heart rate was over 150 (V150 ) and 200 (V200 ) beats per minute respectively. Additionally, a survey of post-race blood samples was also conducted to determine whether high thyroxine concentrations were common in racehorses. STUDY DESIGN A randomised, crossover, trial was performed in six healthy Standardbred racehorses. METHODS Study 1: T4 was determined in 50 post-race samples from a single Standardbred meet. Study 2: Research horses were trained to fitness and then randomised to one of three treatments: carrier, 0.1 mg/kg thyroxine or 0.25 mg/kg thyroxine for 2 weeks. Horses completed a standardised exercise treadmill test (SET) to fatigue on the last day of treatment. Serum free and total thyroxine and triiodothyronine were determined on the day of SET testing. Blood lactate and ECG data were collected during the SET at 6, 8, 10, 11, and 12 m/s and during recovery. The effect of treatment and SET on heart rate and blood lactate was examined using generalised linear mixed models. Post hoc analysis was adjusted for multiple comparisons using Tukey's Test. Data were expressed as mean ± standard deviation and P < .05 was considered significant. RESULTS Study 1: The median T4 value in this population of horses was 2.00 µg/dL (laboratory's normal range 1.5-4.5 µg/dL) and 3 of 50 racehorses had values above the laboratory reference range. Study 2: Levothyroxine at 0.25 mg/kg resulted in higher heart rates during SET (199 ± 30, 223 ± 17 and 239 ± 9 bpm at 6, 8 and 10 m/s respectively) and recovery (144 ± 20 and 119 ± 15 at 5 and 15 min) as compared to placebo (176 ± 18, 203 ± 10 and 219 ± 6 bpm at 6, 8, and10 m/s and 126 ± 5, 102 ± 11 at 5-15 minutes respectively). Three of six horses developed cardiac arrhythmias including atrial fibrillation. MAIN LIMITATIONS A relatively small number of animals were used and a SET is not identical to actual racing conditions. CONCLUSIONS Supra-physiologic thyroxine supplementation caused a decreased V200 during a standard exercise test and may result in cardiac arrhythmias.
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Affiliation(s)
- Janice Kritchevsky
- Department of Veterinary Clinical Sciences, Purdue University College of Veterinary Medicine, West Lafayette, IN, USA
| | - Carla Olave
- Department of Veterinary Clinical Sciences, Purdue University College of Veterinary Medicine, West Lafayette, IN, USA
| | - Stacy Tinkler
- Department of Veterinary Clinical Sciences, Purdue University College of Veterinary Medicine, West Lafayette, IN, USA
| | - Melissa Tropf
- Department of Veterinary Clinical Sciences, Purdue University College of Veterinary Medicine, West Lafayette, IN, USA
| | - Kathleen Ivester
- Department of Veterinary Clinical Sciences, Purdue University College of Veterinary Medicine, West Lafayette, IN, USA
| | - Lauren Forsythe
- Davis School of Veterinary Medicine, University of California, Davis, CA, USA
| | - Laurent Couetil
- Department of Veterinary Clinical Sciences, Purdue University College of Veterinary Medicine, West Lafayette, IN, USA
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Ferlazzo A, Cravana C, Fazio E, Medica P. The different hormonal system during exercise stress coping in horses. Vet World 2020; 13:847-859. [PMID: 32636578 PMCID: PMC7311877 DOI: 10.14202/vetworld.2020.847-859] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 04/03/2020] [Indexed: 12/19/2022] Open
Abstract
The review discusses the hormonal changes during exercise stress. The exercise generally produces a rise of adrenaline (A), noradrenaline (NA), adrenocorticotropic hormone (ACTH), cortisol, glucagon, growth hormone, arginine vasopressine, etc., and a drop of insulin. The hormonal events during reestablishment of homeostasis due to exercise stress can be divided into a catabolic phase, with decreased tolerance of effort, and reversible biochemical, hormonal and immunological changes, and an anabolic phase, with a higher adaptive capacity, and enhanced performance. The two main hormonal axes activated in the catabolic phase are sympathetic–adrenal–medullary system and hypothalamic-pituitary-adrenal (HPA) axis, while in the anabolic phase, growth hormone-insulin-like factor I axis, and gonadal axes. The hormonal responses during exercise and recovery can be regarded as regulatory and integrated endocrine responses. The increase of catecholamines and ACTH is dependent on the intensity of exercise; a marked increase in plasma A occurs during exercises with high emotional content. The response of cortisol is correlated with the duration of exercise, while the effect of exercise duration on b-endorphin changes is highly dependent on the type of exercise performed. Cortisol and b-endorphin changes usually occur in phase, but not during exercises with high emotional content. Glucocorticoids and iodothyronines are involved in meeting immediate energy demands, and a model of functional interactions between HPA axis and hypothalamic-pituitary-thyroid axis during exercise stress is proposed. A modulation of coping responses to different energy demanding physical activities required for sport activities could be hypothesized. This review supports the proposed regulation of hypophysiotropic TRHergic neurons as metabolic integrators during exercise stress. Many hormonal systems (ghrelin, leptin, glucose, insulin, and cortisol) are activated to control substrate mobilizations and utilization. The cardiovascular homeostasis, the fluid and electrolyte balance during exercise are highly dependent on vasoactive hormones (antidiuretic hormone, atrial natriuretic peptide, renin–angiotensin–aldosterone, and prostaglandins) control.
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Affiliation(s)
- Adriana Ferlazzo
- Department of Veterinary Sciences, Unit of Veterinary Physiology, Polo Universitario Annunziata, Messina University, 98168 Messina, Italy
| | - Cristina Cravana
- Department of Veterinary Sciences, Unit of Veterinary Physiology, Polo Universitario Annunziata, Messina University, 98168 Messina, Italy
| | - Esterina Fazio
- Department of Veterinary Sciences, Unit of Veterinary Physiology, Polo Universitario Annunziata, Messina University, 98168 Messina, Italy
| | - Pietro Medica
- Department of Veterinary Sciences, Unit of Veterinary Physiology, Polo Universitario Annunziata, Messina University, 98168 Messina, Italy
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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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Ferlazzo A, Cravana C, Fazio E, Medica P. Is There an Interplay Between the Hypothalamus-Pituitary-Thyroid and the Hypothalamus-Pituitary-Adrenal Axes During Exercise-Stress Coping in Horses? J Equine Vet Sci 2018. [DOI: 10.1016/j.jevs.2017.08.018] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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Tangyuenyong S, Nambo Y, Nagaoka K, Tanaka T, Watanabe G. Sensitive radioimmunoassay of total thyroxine (T4) in horses using a simple extraction method. J Vet Med Sci 2017; 79:1294-1300. [PMID: 28603213 PMCID: PMC5559379 DOI: 10.1292/jvms.17-0133] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Most thyroid hormone determinations in animals are based on immunoassays adapted from those used to test human samples, which may not reflect the actual values of thyroid hormone in horses because of the presence of binding proteins. The aims of the present study were i) to establish a novel radioimmunoassay (RIA) using a more simple and convenient method to separate binding proteins for the measurement of total thyroxine (T4) in horses and ii) to validate the assay by comparing total T4 concentrations in yearling horses raised in different climates. Blood samples were collected from trained yearlings in Hokkaido (temperate climate) and Miyazaki (subtropical climate) in Japan and from adult horses in estrus and diestrus. T4 was extracted from both serum and plasma using modified acid ethanol cryo-precipitation and sodium acetate ethanol methods. Circulating total T4 concentrations were determined by RIA. T4 concentration by sodium acetate ethanol was appropriately detectable rather than sodium salicylate method and was the same as for acid ethanol method. Furthermore, this sodium acetate ethanol method required fewer extraction steps than the other methods. Circulating T4 concentrations in yearlings were 225.98 ± 20.89 ng/ml, which was higher than the previous reference values. With respect to climate, T4 levels in Hokkaido yearlings tended to be higher than those in Miyazaki yearlings throughout the study period. These results indicated that this RIA protocol using a modified sodium acetate ethanol separation technique might be an appropriate tool for specific measurement of total T4 in horses.
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Affiliation(s)
- Siriwan Tangyuenyong
- Department of Basic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan.,Laboratory of Veterinary Physiology, Cooperative Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan
| | - Yasuo Nambo
- Department of Basic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan.,Department of Clinical Veterinary Science, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-0834, Japan
| | - Kentaro Nagaoka
- Department of Basic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan.,Laboratory of Veterinary Physiology, Cooperative Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan
| | - Tomomi Tanaka
- Department of Basic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan.,Laboratory of Veterinary Reproduction, Cooperative Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan
| | - Gen Watanabe
- Department of Basic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan.,Laboratory of Veterinary Physiology, Cooperative Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan
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Fazio E, Medica P, Cravana C, Pellizzotto R, Fragalà S, Ferlazzo A. Dynamics of Total and Free Iodothyronines of Jumping Horses on the Responses to Competition and Transport. J Equine Vet Sci 2015. [DOI: 10.1016/j.jevs.2014.11.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Ferlazzo A, Fazio E, Cravana C, Medica P. Changes of Circulating Total and Free Iodothyronine in Horses After Competitive Show Jumping With Different Fence Height. J Equine Vet Sci 2014. [DOI: 10.1016/j.jevs.2014.03.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Mendoza FJ, Perez-Ecija RA, Toribio RE, Estepa JC. Thyroid hormone concentrations differ between donkeys and horses. Equine Vet J 2012; 45:214-8. [PMID: 22909401 DOI: 10.1111/j.2042-3306.2012.00622.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
REASONS FOR PERFORMING STUDY Reference intervals for thyroid hormones (TH) concentrations have not been previously established for donkeys, leading to potential misdiagnosis of thyroid disease. OBJECTIVES To determine the normal values of TH in healthy adult donkeys and compare them to TH values from healthy adult horses. METHODS Thirty-eight healthy Andalusian donkeys and 19 healthy Andalusian horses from 2 different farms were used. Donkeys were divided into 3 age groups: <5, 5-10 and >11 years and into 2 gender groups. Serum concentrations of fT3, tT3, rT3, fT4 and tT4 were quantified by radioimmunoassay. All blood samples were collected the same day in the morning. None of the animals had received any treatment for 30 days prior to sampling or had any history of disease. Both farms were in close proximity and under similar management. Differences between groups were determined using a one-way ANOVA analysis followed by Fisher's LSD test. P<0.05 was considered significant. RESULTS Serum TH concentrations were higher in donkeys than in horses (P<0.01). Donkeys <5 years had higher serum rT3, fT4 and tT4 concentrations than donkeys >5 years (P<0.05). Furthermore, older donkeys (>11 years) had lower serum fT3 and tT3 concentrations than younger donkeys' groups (<5 and 5-10 years, P<0.05). TH concentrations were not different between genders (fT3: P = 0.06; tT3: P = 0.08; rT3: P = 0.15; fT4: P = 0.89; and tT4: P = 0.19). CONCLUSIONS Thyroid hormone concentrations are different between healthy adult donkeys and horses. POTENTIAL RELEVANCE Establishing species-specific TH reference ranges is important when evaluating clinicopathologic data in equids in order to avoid the misdiagnosis of thyroid gland dysfunction. Further studies to elucidate the physiological mechanisms leading to these differences are warranted.
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Affiliation(s)
- F J Mendoza
- Department of Animal Medicine and Surgery, Universidad of Cordoba, Spain.
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Jose-Cunilleras E, Viu J, McKenzie E. Science in brief: Clinical news from the 8th ICEEP conference 2010: What more can we learn from haematology and serum biochemistry in athletic horses? Equine Vet J 2012; 44:130-2. [DOI: 10.1111/j.2042-3306.2011.00460.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Cravana C, Medica P, Prestopino M, Fazio E, Ferlazzo A. Effects of competitive and noncompetitive showjumping on total and free iodothyronines, β-endorphin, ACTH and cortisol levels of horses. Equine Vet J 2011:179-84. [PMID: 21059003 DOI: 10.1111/j.2042-3306.2010.00264.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
REASONS FOR PERFORMING STUDY Limited knowledge exists about the differentiated effects of competitive and noncompetitive showjumping on thyroid function and relationships with hypothalamic-hypophysis-corticoadrenal hormones. OBJECTIVES To obtain preliminary data about differentiated effects of competitive and noncompetitive showjumping on total and free iodothyronines, β-endorphin, ACTH and cortisol of horses. MATERIAL AND METHODS Five trained healthy jumper horses were studied during competitive and noncompetitive showjumping, performed in the same circuit design over 10 fences of 1.10 m. Hormone levels before, 5 and 30 min post exercise were recorded. Serum iodothyronines and cortisol concentrations were measured in duplicate utilising EIA kits. Serum ACTH and plasma β-endorphin concentrations were analysed in duplicate utilising RIA kits. Two-way RM ANOVA was applied to test for effects of interaction between different type of session and time. Significant differences between post exercise and basal values were established using Bonferroni's multiple comparison test. A linear correlation analysis (Pearson's method) was performed to analyse the relationships between total and free iodothyronines and between iodothyronines and β-endorphin, ACTH and cortisol. RESULTS In sampling times adopted no statistical different effects of type of session were recorded on hormone variables. Sampling time affected ACTH (F = 4.25; P < 0.02) and T(4) (F = 4.43; P < 0.02) post exercise changes. During the noncompetitive session, significant correlations existed between T(4) and β-endorphin (r = -0.56), ACTH (r = -0.65), between β-endorphin and ACTH (r = 0.52) and between T(3) and fT(3) (r = 0.72); during competition between β-endorphin and T(3) (r = -0.67), fT(3) (r = -0.59). CONCLUSIONS These preliminary results could demonstrate correlations between thyroid hormones and β-endorphin response to showjumping, although no definitive conclusion can be produced concerning the relationships between HPA and thyroid function during exercise.
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Affiliation(s)
- C Cravana
- Department of Morphology, Unit of Veterinary Physiology, Faculty of Veterinary Medicine, Polo Universitario Annunziata, University of Messina, Messina, Italy.
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Ferlazzo A, Medica P, Cravana C, Fazio E. Effects of fence height on total and free iodothyronine changes in horses after experimental show jumping sessions. Equine Vet J 2011:110-5. [PMID: 21058991 DOI: 10.1111/j.2042-3306.2010.00252.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
REASONS FOR PERFORMING STUDY Involvement of thyroid function on performance warrants further investigation as limited data exists on the effects of showjumping on the dynamics of total and free iodothyronines. OBJECTIVES To investigate the response of circulating total and free iodothyronines in horses to experimental showjumping sessions and compare with the effects normally induced by competition and determine if fence height has any effect. MATERIALS AND METHODS Using a randomised crossover study design 6 trained horses were studied during experimental showjumping sessions over 10 fences of different height: 1.00 m (Session 1), 1.10 m (Session 2), 1.20 m (Session 3). Hormone levels were recorded before, after warm-up, 5 and 30 min post exercise. T(3), T(4), fT(3), fT(4) concentrations were analysed by ELISA/competition using streptavidin technology. RM-ANOVA was applied to test for any differences in basal and warm-up values of different sessions. Two way RM-ANOVA was applied to test for any effects of interaction between fence height and time. The differences between individual means over time were assessed using a post hoc multiple comparison test (Bonferroni). RESULTS Basal T(4) changes over the sessions (P < 0.05) were recorded. After warm-up, T(4) concentration results were lower than basal in Session 1 (P < 0.05). Higher than basal values were recorded 30 min post exercise for T(3) (P < 0.001), T(4) and fT(4) (P < 0.01) in Session 2 and for T(4) (P < 0.05) and fT(4) (P < 0.01) in Session 3. The interaction fence height/time results were significant on T(3) (P < 0.03) and fT(4) (P < 0.03); sampling time on T(3) (P < 0.0007), T(4) (P < 0.001) and fT(4) (P < 0.002) post exercise changes. CONCLUSION Showjumping over the highest fences induced a release of T(3) from skeletal muscle, probably due to 5'-desiodase activity and increase of fT(4), due to thyroid stimulation and/or changes in capacity to bind iodothyronines.
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Affiliation(s)
- A Ferlazzo
- Department of Morphology, Biochemistry, Physiology and Animal Production, Unit of Veterinary Physiology, Faculty of Veterinary Medicine, Polo Universitario Annunziata, University of Messina, Messina, Italy.
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LELEU C, HAENTJENS F. Morphological, haemato-biochemical and endocrine changes in young Standardbreds with ‘maladaptation’ to early training. Equine Vet J 2010:171-8. [DOI: 10.1111/j.2042-3306.2010.00273.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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