Thyroid hormones in small ruminants: effects of endogenous, environmental and nutritional factors

Abstract

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.Keywords: goats, nutrition, seasons, sheep, thyroid hormones IntroductionAppropriate thyroid gland function and activity of thyroid hormones (TH) are considered crucial to sustain the productive performance in domestic animals (growth, milk, hair fibre production) and circulating TH can be considered as indicators of the metabolic and nutritional status of the animals (Riis and Madsen, 1985;Todini et al., 2007). Changes of blood TH concentrations are an indirect measure of the changes in thyroid gland activity. Many papers report marked seasonal variation in thyroid activity and in blood TH concentration. These hormone variations are particularly important in the free-ranging and grazing animals, whose main physiological functions (feed intake, reproduction, hair growth) are markedly seasonal. This is the case of small ruminants traditionally reared. Such variations in hormone concentration, in fact, allow the animals to adapt their metabolic balance to different environmental conditions, variations in nutrient requirements and availability, and to homeoretic changes during different physiological stages.The present paper aims to re...

The effect of maternal nutrition level during the periconception period on fetal muscle development and plasma hormone concentrations in sheep

“…These results are consistent with the stress response to undernutrition, so release of cortisol from adrenal cortex may increase associated with decreased plasma insulin concentrations. Previous studies have indicated that long-term maternal undernutrition in sheep influences both maternal and fetal plasma free T3 and T4 hormone concentrations (Rae et al, 2002;Todini, 2007). However, maternal nutrition intake during periconception period did not alter both maternal and fetal T3 and T4 concentrations in the present study.…”

Influence of seasonal changes on physiological variables, haematology and serum thyroid hormones profile in male Red Sokoto and Sahel goats

“…The primary function of thyroid hormones is to increase metabolic rate in order to maintain a relatively constant body temperature. When the AT increases, serum levels of thyroid hormones decrease and vice versa (Todini 2007). Thus, suggesting that as seasons change, breeds that can effectively regulate thyroid hormone secretion may survive better, particularly in the tropical countries where animals are not be provided with special housing according to the prevailing season of the year.…”

Histological and immunohistochemical changes of the thyroid gland during the foetal and postnatal period of development in indigenous Large White crossbred pigs

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