Masters Theses

Date of Award

6-1957

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Husbandry

Major Professor

Charles S. Hobbs

Committee Members

R. L. Murphree, H. V. Shirley Jr.

Abstract

The growth of any organism is determined by the interaction between environmental factors and the genotype of the individual. The mechanisms which operate to control hereditary growth patterns are still little understood. But it is well-known that genes are concerned in the establishment and the maintenance of enzyme systems, and inherited endocrine patterns are involved in determining, in part, the hereditary growth limitations. Endocrine patterns can, of course, be affected by genetic control over those enzyme systems concerned with the synthesis of humoral substances. (Nutrition Review, 1954).

Unfortunately, the genetic make-up of an organism responsible for a high expression of functional processes such as the growth rate or the capacity to produce large litters, seemed at times to be transmitted from it's parents with distressing irregularity. Extreme expression of functional processes is made possible only by a suitable (perhaps even a specific) combination of a large number of genes (derived from the two parents) that complement one another. It is recognized to be extremely difficult if not impossible to exclude from the desired combination a few conflicting or antagonistic genes which prevent the desirable ones from producing their maximum potential effect. It might be possible to utilize exogenous sources of hormones or combinations of hormones to alter the growth patterns of animals to the benefit of man. The application of knowledge of endocrine processes to animal production, in the past, has been limited by the fact that many of the hormones were expensive. Furthermore, methods for controlling the activity of the endocrine glands were not well-defined.

The hormones of the thyroid gland (thyroxine) and of the female sex gland (estrogen) have been synthesized and are now commercially available at reasonable prices. Since both thyroxine and estrogen are known to be involved in growth processes in animals it seemed desirable to study the role of these hormones in growth in swine and laboratory animals.

An attempt has been made to present a comprehensive review of the available literature concerning the effects of hyper- and hypo-thyroidism, natural and synthetic estrogens on the growth rate and efficiency of feed utilization in farm animals.

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