Masters Theses

Barry Reit

Date of Award

3-1968

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Husbandry

Major Professor

R. L. Murphree

Committee Members

G. M. Merriman, D. O. Richardson

Abstract

Although considerable work has been conducted on thyroid and parathyroid function in several species of animals, thus far, such studies in swine are obscure. The results of early studies on the effects of thyroidectomy in other species were badly clouded because of the simultaneous removal of the parathyroids. It is now accepted that the two organs are anatomically and physiologically separate structures. In most mammals the thyroid gland consists of two lobes--one on each side of the trachea close to its junction with the larynx. The Lobes are usually connected by an isthmus crossing the ventral surface of the trachea. The pig is an exception in that the thyroid gland is a mono lobed structure located on the ventral surface of the trachea just above the thoracic aperture. The parathyroids, present in amphibians, reptiles, birds and mammals, are believed to have essentially the same function. There are usually two pairs of parathyroids. Marked variations the position of the glands are seen in the different species, and, indeed, the position varies somewhat in animals of the same species. Location of these pyriform bodies is commonly on the posterior surface of the lateral lobes of the thyroid. Again, the pig proves to be an exception by having only two parathyroid glands--one in each anterior tip of the thymus gland (Schlotthauer and Higgins, 1934; Littledike, 1965). Optimal activity in animals is expected to occur when there is a proper balance of secretory activity of all the endocrine glands. Both the thyroid and parathyroid glands play an important part in this balance. Thyroid effects on metabolism, growth, and sexual maturity are well known; parathyroid regulation of calcium and phosphorus metabolism in many species is also well documented. Extirpation of these glands produces a well-established syndrome of clinical symptoms; however, most of this knowledge is based on data compiled from research on dogs, cats, and rats. Relatively little attention has been devoted to the effects of the hormones of these glands on calcium and phosphorus metabolism in the pig. The present investigation was conducted to determine the specific effects of parathyroidectomy and thyroidectomy on levels of calcium and phosphorus in the blood. The pig was chosen as the experimental animal because it is the only mammal that has an anatomically separated parathyroid and thyroid gland.

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