Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Animal Husbandry

Major Professor

Charles S. Hobbs

Committee Members

R. L. Murphree, Harold J. Smith, L. N. Skold


During recent years much attention has been given to studies of lowered fertility in cows; however, relatively little study has been given to the problem of lowered fertility in bulls. Some bulls show lowered fertility due to low sperm concentration, poor motility, or various other seminal defects. Occasionally bulls are observed which produce semen of high quality, but are so lacking in sexual drive that they are of little value in a breeding program.

The role of the endocrine system in the development and maintenance of fertility has long been recognized. The gonado-tropic hormones from the anterior pituitary governs the development and function of the testes. Under the stimulus of the gonadotropic hormones the interstitial cells of the testes secrete the male hormone, testosterone. Testosterone stimulates the growth of the accessory sexual organs and the development of the secondary male characteristics. Sex drive is directly controlled by the level of testosterone production of the testes.

Becerra (1952) stated that many cases of lowered fertility in bulls can be corrected temporarily by injection of the gonadotropic hormones and/or sex hormones; however, it is possible that prolonged administration of these agents may actually suppress sperm production, due to impairment of pituitary function.

The question arises as to how long such treatments may be administered without deleterious effects. This study was initiated to obtain information regarding the effects of the administration of testosterone cyclopentylpropionate on semen characteristics and sexual behavior in bulls over a period of time comparable to a normal breeding season in beef cattle.

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