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ANTIBIOTICS, HORMONES, AND TRANQUILIZERS IN ANIMALS 
J. F. Sykes, J. W. Thomas, J. Bitman,and C. F. Winchester ! 
INTRODUCTION 
The use of antibiotics, hormones, andtranquilizers as feed additives or by other forms 
of administration for improving efficiency of livestock and poultry production introduces 
several problems beyond an evaluation of their usefulness for the purpose proposed. In 
addition to the possibility that these substances may accumulate in the tissues and animal 
products used for human consumption, there exists the possibility that the metabolic 
products of these compounds may also persistand produce harmful effects when consumed. 
The problem of exposure of other animals or foods to the excreta from treated animals 
with possible harmful results to both humans and animals must also be considered. A 
detailed knowledge of absorption, excretion, metabolism, and stability of these materials 
would seem to be a prerequisite for estimating the problems that might arise in their use 
or for the solution of these problems as they arise. 
In this presentation, we have attempted to review to what extent this area of work has 
been considered in the research associated with the use of these compounds and to 
compile information on their disposal and metabolism that would provide guidelines for 
the nature of future investigations. We have restricted our review to the antibiotics, 
hormones, and tranquilizers, rather than try to examineall the possible compounds with- 
in each class. Our discussion is also restricted to those compounds in general use at 
present or those proposed for use by livestock. 
The problem of obtaining precise and meaningful information in these areas of work 
is very great. Most of these compounds are complex organic molecules. While tests and 
analytical methods exist for these compounds, they are frequently not specific for a 
particular material. This imposes the problem of developing adequate extraction and 
purification procedures before reliance can be placedonthe analytical results. Biological 
assay methods are useful in tracing the primary activity of interest but give little precise 
information on the nature of metabolic transformations. These methods in general suffer 
from lack of precision, particularly when dealing with micro quantities in tissues and 
excreta. 
ANTIBIOTICS 
Absorption 
When administered by any parenteral route the antibiotics are all quickly absorbed 
and translocated from the site of injection. When given orally some are absorbed quickly 
1Veterinarian (Nutrition) and Leader, Nutrition and Physiological Investigations; Dairy Husbandman; Chemist, Dairy Cattle 
Research Branch; and Animal Husbandman (Nutrition), respectively, Animal Husbandry Research Division, Agricultural Research 
Service, U. S. Department of Agriculture. 
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