• EndocrineUngulates

Endocrine diseases of Ungulates

In order to survive, animals must constantly adapt to changes in the environment and it is the endocrine system that works to bring about these adaptations. In general, the endocrine system brings about longer-term adaptations by sending out chemical messengers called hormones into the intracellular fluid or the bloodstream. The endocrine system is very influential and relates to most, if not all the other principle systems of the body. It is accountable for the production of hormones as well as the regulation and monitoring of them as well. These hormones function as chemical messengers throughout the body. Through disparate mechanisms, they are able to generate specific responses in target cells or organs.

The hormones secreted by the endocrine system come from a variable range of different places. Amidst those culpable for hormone production are the glands as well as a few organs as well. The primary glands associated mostly with hormone production are the adrenal, pituitary, thyroid, parathyroid and the thymus. The organs, which also perform a substantial role are the kidneys, pancreas, gonads, heart and alternative parts of the digestive tract. The hormones which are regarded of greatest importance for maintenance of the body in ungulates and averting disease are;

• Growth hormone GH

• Luteinizing hormone LH

• Follicle stimulating hormone FSH

• Thyroid stimulating hormone TSH

• Adrenocorticotrophic hormone ACTH

• Anti-diuretic hormone ADH

• Adrenaline

• Noradrenaline

• Aldosterone

• Cortisol

• Insulin

• Glucagon

• Testosterone

• Oestrogen

It is these hormones in which enable the endocrine system in ungulates to promote growth, development, reproduction and behaviour among other traits too. Any deviation away from the regulatory level of these hormones listed above in ungulates will result in specific hormonal diseases to the animal in question.

Hypothyroidism is an endocrine disease associated with the thyroid gland. The thyroid gland is located on the ventral side of the trachea on both sides just caudal to the larynx and vary in appearance amongst ungulates. In the horse and cow it consists of two lobes, which are connected by an isthmus. In the horse, each lobe appears more oval in shape in comparison to the cow which takes up a rectangular appearance. In the pig, the thyroid gland is an unpaired compact organ with a granular like presence.

The main two hormones relating to the thyroid gland are thyroxine (T4) and triiodothyronine (T3). They are produced by follicular cells before being released into the bloodstream. Hypothyroidism is also referred to as ‘goitre’ and a deficiency in these hormones will result in this endocrine disease, causing the overall well-being of the animal to deteriorate, such examples being, their decreased metabolism of lipids, carbohydrates and proteins, their desire and willingness to exercise and their overall growth.

Triiodothyronine is mainly derived from thyroxine, although both hormones are dependant on the presence of iodine in the diet of the animal to ensure adequate secretion.(Bragulla,2009).The secretion of thyroid hormones is coordinated by the negative feedback control in response to the hypothalamic-pituitary thyroid axis. In the pituitary, thyrotropin releasing hormone (TRH) attaches to thyrotrophic cells which stimulates the secretion of the thyroid stimulating hormone (TSH) thus, causing thyroid hormone synthesis and secretion.

In cattle, hypothyroidism is the most prevalent thyroid disease as a result of insufficient thyroglobin synthesis and secretion. However, on saying this, in the modern era this endocrine disorder is still quite rare owing to the fact that modern animal feeds encompass sufficient levels of iodine(Vetbook,2012).An animal suffering with hypothyroidism will have a large visual lump on its neck in the region of the larynx, which can vary in size and can be as small as a marble in some cases and may be initially difficult to observe. The majority of hypothyroidism cases are due to an iodine inadequacy, and its more prevalent in young/newborn calves than adult animals.(Jackson,2017).These young animals born with hypothyroidism are medically known as ‘congenital goitre’. There are few reasons why the pregnant cow/horse/sheep may be suffering from iodine deficiency.

Depending on the time of year, the amount of rainfall will vary in a region. High rainfall will ensure good growth and fertile lands with lush grass available throughout this period. This can be a negative problem for the animal as it is less likely to consume forage from surface soils which would contain a range of nutritional minerals including iodine. We can be of the opinion that hypothyroidism is more likely to occur if there is an endless supply of quality grass with a low stocking density. In some regions present across the world, sandy soils are most common (African plains) and pregnant animals here are much more susceptible to develop an iodine deficiency in contrast to those grazing on textured soils. Goitrogens are compounds present in brassica crops, which can further impede iodine availability. Sheep are more inclined to consume this type of vegetation. Iodine lacking newborn lambs are unable to adapt to harsh wet conditions in juxtaposition to iodine sufficient lambs, therefore, even a slight lack of iodine in lambs which could go easily unnoticed could be a major cause of mortality(Tasmanian Government,2014)

In severe equine cases, foals in particular with hypothyroidism, can be referred to as ‘dysmature’. The shortage of iodine can develop brittle bones, flexor and extensor tendons may become ruptured, and joint problems may be encountered which in turn leaves them unable to stand properly as well as having coats disorders. As well as all of this, the mare can have a prolonged gestation, risking death for both mother and young at the time of parturition.(R.Singh,2013)

Fortunately, certain methods and measures can be taken to inhibit or prolong the onset of hypothyroidism, by ensuring iodine is available and is part of the diet. One method is dosing the pregnant mother with iodine 4-5 months into pregnancy. A further approach would be the use of mineral licks to provide iodine consumption, although this measure may not always be reliable as its hard to know in a herd if the animals affected has consumed the lick or may be put off by the taste of the lick. On top of these, an additional procedure which entails the farmer painting the teats of the cow, ewe and mare with iodine, will allow the young animal to obtain traces of iodine whilst suckling.(Tasmanian Government,2014)