Hypothyroidism in the foal.
Abstract: Hypothyroidism in the foal occurs as two entities because of the separate actions of thyroid hormones in regulation of metabolic rate and in cell differentiation. The hypometabolic state which results in inadequate thermogenesis and lethargy, occurs concurrently with a period when thyroid hormone secretion is inadequate. Also the severity of the concurrent symptoms is related to the degree of hormone inadequacy as measured by plasma concentrations of free T4 and T3. By contrast, the developmental lesions caused by hypothyroidism are often observed during periods when plasma thyroid hormone concentrations are normal. This is because during the development of most tissues there is a period during which deprivation of thyroid hormones leads to developmental defects which may first appear weeks or months later, by which time thyroid hormone levels may have returned to normal. In the foal the critical period for some developmental processes, eg, myelination, is before birth so it is difficult to confirm a pre-natal hypothyroid state as the cause of neonatal neuromuscular incompetence. Post natal developmental lesions of the epiphyses or ossification centres, for example, may also manifest themselves some weeks subsequent to the period during which hypothyroidism existed. Because confirmation of diagnosis using plasma hormone measurements is very difficult in the foal, and because the symptoms of hypothyroidism are not specific, the incidence of confirmed hypothyroidism in foals is low. However there is suggestive evidence that where awareness of the condition exists it is diagnosed frequently. The aetiology is obscure although diet has been implicated.(ABSTRACT TRUNCATED AT 250 WORDS)
Publication Date: 1984-07-01 PubMed ID: 6383812DOI: 10.1111/j.2042-3306.1984.tb01932.xGoogle Scholar: Lookup
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Summary
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The research article discusses the occurrence and impact of hypothyroidism in young horses, or foals. Additionally, difficulties in diagnosing the condition are highlighted due to variations in thyroid hormone levels and non-specific symptoms in affected animals. Similarly, the exact causes remain unclear, though diet has been suggested as a possible factor.
Hypothyroidism and its Effects
- The study underlines two manifestations of hypothyroidism amid foals. Firstly, it can induce a hypometabolic state, resulting in reduced thermogenesis and lethargy, especially during periods of inadequate thyroid hormone secretion. Secondly, it can lead to developmental lesions often detected when plasma thyroid hormone concentrations are normal.
- The severity of the concurrent symptoms relating to the hypometabolic state is directly proportional to the extent of hormone inadequacy, as evidenced by plasma concentrations of free T4 (thyroxine) and T3 (triiodothyronine).
Developmental Implications of Hypothyroidism
- Hypothyroidism disturbs tissue development, often causing developmental defects that may not become visible until weeks or months later, by which time thyroid hormone levels could have normalized. This presents a particular challenge in foals, as key developmental processes like myelination take place before birth, making it difficult to determine whether a prenatal hypothyroid state is the cause of neonatal neuromuscular incompetence.
- Furthermore, other developmental abnormalities, such as lesions of the growth plate or ossification centres, might only present weeks after the hypothyroid state, making diagnosis additionally challenging.
Challenges in Diagnosis and Potential Causes
- Diagnosing hypothyroidism in foals is complex because of fluctuating hormone levels and non-specific symptoms. Thus, confirmed cases of hypothyroidism in foals are limited. However, where there is awareness of the condition, it seems to be diagnosed more frequently.
- The exact cause of hypothyroidism in foals remains uncertain, but diet has been suggested as a contributing factor, implying that nutritional management is an important aspect of preventing or managing the condition.
Cite This Article
APA
Irvine CH.
(1984).
Hypothyroidism in the foal.
Equine Vet J, 16(4), 302-306.
https://doi.org/10.1111/j.2042-3306.1984.tb01932.x Publication
Researcher Affiliations
MeSH Terms
- Animals
- Animals, Newborn / blood
- Animals, Newborn / growth & development
- Animals, Newborn / physiology
- Female
- Horse Diseases / blood
- Horse Diseases / diagnosis
- Horse Diseases / drug therapy
- Horse Diseases / physiopathology
- Horses / growth & development
- Hypothyroidism / blood
- Hypothyroidism / diagnosis
- Hypothyroidism / drug therapy
- Hypothyroidism / physiopathology
- Hypothyroidism / veterinary
- Pregnancy
- Thyroid Hormones / physiology
- Thyroid Hormones / therapeutic use
- Thyroxine / blood
- Triiodothyronine / blood
Citations
This article has been cited 5 times.- Müller V, Toribio RE, Dembek K, Moraes BSS, Mousquer MA, Curcio BR, Nogueira CEW. Serum cortisol and thyroid hormone concentrations and survival in foals born from mares with experimentally induced ascending placentitis. J Vet Intern Med 2020 May;34(3):1332-1338.
- McLaughlin BG, Doige CE, McLaughlin PS. Thyroid hormone levels in foals with congenital musculoskeletal lesions. Can Vet J 1986 Jul;27(7):264-7.
- Allen AL, Doige CE, Fretz PB, Townsend HG. Hyperplasia of the thyroid gland and concurrent musculoskeletal deformities in western Canadian foals: reexamination of a previously described syndrome. Can Vet J 1994 Jan;35(1):31-8.
- Stoeckle SD, Stage HJ, Gehlen H. Thyroid Disease in Horses-Retrospective Case Series on Patients Examined for Thyroid Disease in an Equine University Clinic (2009-2024). Vet Sci 2025 Nov 27;12(12).
- Pasolini MP, Auletta L, De Biase D, Vaccaro E, Del Prete C, Montano C, de Chiara M, Di Napoli E, Paciello O, Piegari G. Clinical and Pathological Features of Flexural Deformities Associated with Myopathies in Foals. Vet Sci 2025 Jun 6;12(6).
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