most of the other compounds do, they have a place as feed additives for protection of 
vitamins and fats against oxidation. Surfactants have taken a somewhat limited place of 
interest as have enzymes. Both would appear to function as digestive aids in promoting 
greater efficiency in feed utilization. 
A great number of compounds within the general groups indicated have been de- 
veloped synthetically or biologically in recent years. In the earlier developments the 
concern was primarily for possible use inhuman medicine. The great interest in livestock 
feed additives has spurred biochemists to develop compounds primarily for this purpose. 
Thus far we have attempted to portray the chronological development research-wise 
of the feed additives problem over the last 20 years. In several cases the quickness with 
which research findings have been applied to feeding practice has been phenomenal, al- 
though in others there has been little or no application. The reasons for adoption of some 
of these research findings to production practices undoubtedly rest primarily on the fi- 
nancial returns. These increased returns are to be found in the acceleration in rate of 
gain, in feed savings, and sometimes in decreases in death losses. We will undertake to 
point up some of these factors in use of feed additives. 
At the onset, it must be pointed out that, in summarizing the material, there is the 
hazard of over-simplification, especially in the presentation of average figures and in 
drawing conclusions. It must be kept in mind that widely divergent figures are contained 
in the tables of average results. Furthermore, they have not been evaluated for statistical 
significance. 
BEEF CATTLE 
The use of diethylstilbestrol in the fattening of beef cattle was adapted to feedlot 
practice remarkably quickly and extensively. Following acceptance of the new drug ap- 
plication in 1954, the oral feeding procedure was soon used on a widespread scale, Within 
a 2-year period estimates indicated that about 60 percent of the cattle in feedlots were 
receiving the compound. Subsequently, the figure rose to 70 percent and more recently 
to 80 percent. The distribution and rationing procedure provides 10 mg. per animal per 
day. Many feeding trials have been conducted in which rates of gain, feed consumption, 
and carcass data have been obtained. The gain stimulation and feed savings have been 
consistently favorable as a general rule. Carcass merit has been maintained in most 
comparisons. The advantage to the producers has rested in the shorter feeding period 
and reduced feed requirement. A summary by Burroughs (4) from Iowa State University 
(Table 1) shows an average increase in rate of gain of 13 percent and a feed saving of 10 
percent for fattening cattle receiving 10 mg.ofstilbestrol as compared to control groups. 
His figure for increased returns peranimalis $6.94, These favorable results undoubtedly 
explain the widespread practice that use of the drug has attained. 
Implanting pellets in the ears of feedlot cattle have likewise increased rate of gain 
and decreased feed requirement. Comparisons of the effectiveness of different amounts 
of stilbestrol indicate that implantation of 36 mg. gave a gain advantage of 15 percent and 
a feed saving advantage of 10 percent. Carcass grades were slightly lower, however. 
Whether the financial return is as favorable for pellet-treated animals as for orally 
treated is not clear. 
Numerous experiments have been conducted on other hormone products. Hexestrol, 
administered orally, has given results about equal to those just cited for stilbestrol to 
which it is closely related chemically. Oral feeding of dienestrol has been effective, 
also, Implants of progesterone, combined with estradiol, have given responses approach- 
ing those of stilbestrol. Besides the feedlot studies, there has been much interest in 
hormone treatment of young cattle on pasture as well as wintering studies. Positive 
responses have been obtained especially with stilbestrol. 
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