Experimental work thus far reported on other feed additives has not shown much 
promise. Possibly the use of enzymes under special dietary conditions may find a useful 
place. The few tests with tranquilizers have not shown real benefits as yet. Nutritionists 
are concerned with other feed additives more properly classed as nutrients such as trace 
minerals, vitamins, and amino acids. Certain mineral elements are essential yet become 
toxic at high levels. 
PROBLEMS 
Some of the problems in the use of feed adjuncts from the standpoint of animal pro- 
duction were mentioned in the foregoing discussion. Even though many animal feeding 
experiments have been reported, conflicting results leave questions as to practical ap- 
plications and profitableness from use in numerous cases. Obviously, the interrelations 
with other dietary nutrients, the feeds used in the diets, the management of the animals, 
the period in the life cycle, the quantities of the chemicals used, and other related factors: 
influence the responses. 
While the antibiotics probably present fewer problems than the other materials, 
details of the actual manner in which they function still remain in doubt. Some of the 
newer materials have not been studied sufficiently to judge their place and usefulness 
and basic information on the way in which they function in one animal species as com- 
pared to another is largely nonexistent. The combining of two or more materials to 
determine additive effects is complex. The statement is made frequently that it is good 
insurance to include a particular chemical. This may be good investment in some cases 
but used too indiscriminately simply adds to the feed cost. 
A pressing need, especially in the case of hormones, is the development or simpli- 
fication of existing methods applicable to feedstuffs, to body fluids and tissues, and to 
excreta in order to study the metabolic function, the ways in which the materials affect 
metabolism and growth, and how much or howlittle of the material is really needed. With 
such tools, it should be possible to evaluate hormonal capacities of different species and 
strains of animals. Out of this might well come the development through genetic means 
of animals that will not need supplementation through the diet or by implant. 
In the case of stilbestrol, why is it that implants of 12 to 15 mgs. of the material 
have been the effective amount for chickens, whereas for a lamb many times larger, 
this is excessive? Doses of 24 and 36 mgs. are quite effective in 600-pound steers. Are 
the several classes of animals so different in physiological functioning as to require 
these differing ratios to body size? What are the checks and balances in endocrine in- 
terrelations in different species, and in different strains and lines of breeding? 
A major problem area is that of naturally occurring substances in feeds, It has been 
known for sometime that legumes, particularly the cloversand alfalfa, contain substances 
having estrogenic properties. The difficulties in Australia in carrying sheep on subter- 
ranean clover pastures is well known. Ohio sheep farmers have told us how they have 
learned to avoid prolonged use of clover pastures because of poor lamb crops, On the 
other side of the picture are reports pointing to beneficial effects in feeding alfalfa to 
fattening cattle not unlike those obtained with stilbestrol supplementation. 
The Western Utilization Research and Development Division has reported the isola- 
tion of the estrogen, coumestrol, from alfalfa. While the legumes seem to show higher 
contents of estrogenlike substances, other plants show reactivity also. More studies are 
needed to identify the distribution of such compounds in plant life and the cultural prac- 
tices that govern the contents. Should strains of forages be identified and developed to 
supply growth-promoting principles in natural forms? 
Undoubtedly, many more chemicals will be synthesized and tested for use in animal 
production. New ones may replace some of those now being studied and used. Some new 
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