Masters Theses

Date of Award

6-1953

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Husbandry

Major Professor

Charles S. Hobbs

Committee Members

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

Abstract

Livestock producers and feeders are always Interested in ways and means of increasing rate of gain and feed efficiency in fattening animals. Various chemical compounds have been fed or administered to farm animals with variable results in trying to increase rate of gain and feed efficiency.

In the past, some livestock feeders believed that spayed females made mature rapid and efficient gains in the feedlot than unspayed females. On the other hand, others believed that pregnant females made more rapid and more efficient gains than open females. More recently, Hart et al. (1940) concluded that there was no advantage to be gained either from spaying or breeding heifers that are going into the feed lot.

Recent studies have demonstrated, under certain conditions, that subcutaneously administered synthetic female-like sex hormones may increase the growth rate and feed efficiency over that of similar untreated farm animals. The mechanism of this action has not been satisfactorily elucidated.

Diethylstilbestrol, more commonly referred to as stilbestrol, has shown the most promising results of any of the hormonal compounds used in attempting to increase meat production more economically. This compound, a synthetic female-like sex hormone, has an advantage over all other compounds thus far studied in that only a single treatment at the beginning of the trial is required. This synthetic hormone is relatively inexpensive compared to the price of the natural female hormones. For example, the natural hormone, estradiol benzoate, costs approximately fifty-eight times as much as a similar quantity of stilbestrol. Stilbestrol and other synthetic hormones may become widely used on market animals unless the residual effects of the materials used prove to be deleterious.

The author would like to point out that two=thirds of the work reported in this thesis was completed during the spring and summer of 1950. At that time only one report had been published in which stilbestrol had been used in connection with the rate of gain and feed efficiency of sheep.

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