1Dipartimento di Scienze Ambientali - Sezione di Produzioni Animali, Università di Camerino, Via della Circonvallazione 93/95, 62024 Matelica (MC), Italy.
Animal. 2007 Aug;1(7):997-1008. doi: 10.1017/S1751731107000262.
Appropriate thyroid gland function and thyroid hormone activity are considered crucial to sustain the productive performance in domestic animals (growth, milk or hair fibre production). Changes of blood thyroid hormone concentrations are an indirect measure of the changes in thyroid gland activity and circulating thyroid hormones can be considered as indicators of the metabolic and nutritional status of the animals. Thyroid hormones play a pivotal role in the mechanisms permitting the animals to live and breed in the surrounding environment. Variations in hormone bioactivity allow the animals to adapt their metabolic balance to different environmental conditions, changes in nutrient requirements and availability, and to homeorhetic changes during different physiological stages. This is particularly important in the free-ranging and grazing animals, such as traditionally reared small ruminants, whose main physiological functions (feed intake, reproduction, hair growth) are markedly seasonal. Many investigations dealt with the involvement of thyroid hormones in the expression of endogenous seasonal rhythms, such as reproduction and hair growth cycles in fibre-producing (wool, mohair, cashmere) sheep and goats. Important knowledge about the pattern of thyroid hormone metabolism and their role in ontogenetic development has been obtained from studies in the ovine foetus and in the newborn. Many endogenous (breed, age, gender, physiological state) and environmental factors (climate, season, with a primary role of nutrition) are able to affect thyroid activity and hormone concentrations in blood, acting at the level of hypothalamus, pituitary and/or thyroid gland, as well as on peripheral monodeiodination. Knowledge on such topics mirror physiological changes and possibly allows the monitoring and manipulation of thyroid physiology, in order to improve animal health, welfare and production.
适当的甲状腺功能和甲状腺激素活性被认为是维持家畜生产性能（生长、产奶或产毛）的关键。血液中甲状腺激素浓度的变化是甲状腺活动变化的间接衡量标准，循环中的甲状腺激素可以被视为动物代谢和营养状况的指标。甲状腺激素在允许动物在周围环境中生存和繁殖的机制中起着关键作用。激素生物活性的变化使动物能够将其代谢平衡适应不同的环境条件、营养需求和可利用性的变化，以及在不同生理阶段的同源变化。这在自由放养和放牧动物中尤为重要，如传统饲养的小反刍动物，其主要生理功能（采食量、繁殖、毛发生长）明显具有季节性。许多研究涉及甲状腺激素在表达内源性季节性节律中的作用，如产毛（羊毛、马海毛、羊绒）绵羊和山羊的繁殖和毛发生长周期。从绵羊胎儿和新生动物的研究中获得了有关甲状腺激素代谢模式及其在个体发育中的作用的重要知识。许多内源性（品种、年龄、性别、生理状态）和环境因素（气候、季节，以营养为主）能够影响血液中的甲状腺活性和激素浓度，作用于下丘脑、垂体和/或甲状腺，以及外周单脱碘作用。关于这些主题的知识反映了生理变化，并可能允许监测和操纵甲状腺生理，以改善动物的健康、福利和生产。
