THE TOXICITY OF PESTICIDES FOR LIVESTOCK 
R. D. Radeleff and R. C. Bushland! 
INTRODUCTION 
Our objective in the present discussion is to evaluate, in broad terms, the toxicities 
and hazards of modern pesticides for livestock, utilizing the accumulated evidence de- 
rived from our own researches and those of many other scientists. In this evaluation we 
believe we can show that the modern pesticides have been, and are being, used with com- 
plete safety to treated or exposed livestockand that such usage need not introduce hazard- 
ous residues in foods derived from livestock. 
Pesticide development has been primarily in the field of organic chemistry, creating 
thousands of new compounds, but often utilizing those that had existed as chemical curi- 
osities for a number of years. 
Certain persons have repeatedly expressed doubts as tothe adequacy of investigation 
that may have preceded the recommendation of these compounds for farm use. The word 
‘‘adequate’’ has never been defined in this regard, but a general definition is ‘‘equal toa 
requirement or occasion; sufficient; suitable’’, with an alternate of ‘‘barely satisfactory; 
acceptable, but not remarkable.'’ Within this definition we believe the investigations have 
been adequate. 
Before a new pesticide may be registered by the U.S. Department of Agriculture for 
shipment in interstate commerce, evidence must be presented showing that it is effective 
for the proposed usage and is reasonably safe when so used. The required information 
may be supplied by any responsible individual or organization, including other USDA Agen- 
cies. State laws provide similar protection for products marketed within their borders, 
Few chemicals can meet the dual requirements of effectiveness and safety. This is 
exemplified in that the ARS Entomology Research Division of USDA has studied more than 
17,000 new chemicals as insecticides or repellants since 1947. About 3,000 of these 
were proposed and tested for use against livestock parasites, Because of ineffectiveness, 
toxicity hazard, residues in meat or milk, manufacturing difficulties, and other problems, 
most of the 3,000 were eliminated, leaving only 10 synthetic organic insecticides recom- 
mended by the Entomology Research Division for use on livestock during 1959. 
This process of elimination functions in the investigation of all new pesticides, being 
carried out by industrial, commercial, private, and governmental research units. 
The manner in which a chemical is used governs, to some degree, its probable toxi- 
cological hazard for livestock. Materials applied directly to the animals represent the 
greater danger for acute poisoning, while those applied to feed crops usually represent 
the greater danger for subacute or chronic poisoning. 
While a modern pesticide may be put into interstate commerce on the basis of 
scientific «aata which indicate that it is reasonably safe and effective under prescribed 
conditions of use, misuse will inevitably occur. Some misuse is generally anticipated 
and considered in both the recommendations and the registration for use, but it is simply 
not possible toanticipate the extremes of misuse which certain farmers and ranchers can 
devise 
1 Veterinarian in Charge, Animal Disease and Parasite Research Division; and Investigations Leader, Livestock Insects Investiga- 
tions, Entomology Research Division, Agricultural Research Service, U. S. Department of Agriculture, Kerrville, Tex. 
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