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Thyroid Gland - Anatomy & Physiology (view source)

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:[[Reproductive System Overview - Anatomy & Physiology|'''Reproductive system''']] is affected by reduced levels of thyroid hormone causing irregular cycling and decreased libido.

:Finally, in the [[Alimentary System Overview - Anatomy & Physiology|'''alimentary system''']], thyroid hormone increases appetite and feed intake, increases secretion of [[Pancreas - Anatomy & Physiology|pancreatic]] enzymes and increases motility.

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===Influence of external factors===

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'''Euthyroid sick syndrome''': concurrent disease such as starvation, sepsis, trauma or stress can cause a depression in basal thyroid levels as a normal response, to minimise the catabolic effects of thyroid hormones.

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This occurs in many species and may lead to false diagnoses of hypothyroidism or a missed diagnosis of hyperthyroidism.

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<u>'''In horses'''</u>, many factors influence the level of T3 and T4:

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'''In foals''': thyroid hormone concentrations are up to 14 times higher than in horses over the age of 2.

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During normal feeding, T3 and T4 levels increase within two hours of feeding. Undernutrition results in an increase in T4 but T3 levels are unchanged. Excess protein and energy result in a decreased T4 and an increased T3.

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'''In adult horses''': undernutrition results in a decrease in both T3 and T4. Phenylbutazone is also known to decrease T4 levels.

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Thyroid hormone levels increase with age, and are higher during pregnancy and times of low temperature.

==Problems associated with the Thyroid Gland==

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