The vast majority of livestock losses due to pesticides have been the result of either 
deliberate misuse, failure to read the label, orcareless exposure of dangerous chemicals 
where animals could drink or eat them. 
Our discussion is dominated by insecticides because these materials are the most 
widely dispersed in usage, may be applied to animals, may be injected or otherwise in- 
troduced into them, may be put on the animals’ feed as a part of normal plant protection, 
and may be left carelessly exposed. Herbicides represent a smaller part, because their 
use is generally limited to the destruction of undesirable plants in crops not grazed by 
livestock or pasture plants not normally eaten by livestock. Therefore, the opportunities 
for exposure of livestock are usually severely restricted. 
Defoliants and fungicides are even more restricted in use. 
Until 1940, compounds of arsenic, lead, lime, sulfur, and fluorine, almost all of an 
inorganic nature, were the prime insecticides. Arsenicals, copper compounds, oils, and 
chlorates dominated the field of herbicidal chemicals, again primarily as inorganic com- 
pounds. Mercurial and phenolic compounds dominated the fungicide field. Red squill, 
strychnine, phosphorus, and thallium compounds dominated the rodenticide field. 
There was a sprinkling of products from plants. For fumigation, there were carbon 
disulfide, carbon tetrachloride, sulfur, and cyanides. 
The metallic and phenolic compounds offered the greatest hazard to livestock. 
Arsenic and lead have been recognized for years by livestock authorities as being the 
leading causes of poisoning in livestock other thanthe naturally occurring elements, such 
as selenium, fluorine, and molybdenum. 
THE MEANING OF TOXICITY AND HAZARD 
Before going deeper into the problem of the toxicological hazard of pesticides to 
livestock, it is important that we understand the relationship of toxicity to hazard. It is 
axiomatic in the science of toxicology that virtually any chemical or physical entity will 
have harmful effects upon living organisms if applied or consumed in excessive amounts, 
Such daily accepted essentials as sunlight and rain are perfect examples; too much of 
either will destroy plant and animal life. A substance is more or less toxic according to 
the amount required to do damage. The most toxic substance we know is probably the 
botulinus toxin, while some of the least toxic ones are the staple foods we eat. A sub- 
stance becomes a hazard if the normal use, or minor misuse of it, is likely to harm de- 
sirable organisms, regardless of the amount of the substance required compared to other 
toxic materials. 
Because of this relationship, we often find that the less toxic of a pair of compounds 
is actually the more hazardous in use. We have given emphasis to this factor in relation 
to chemicals used in mosquito control (94), and Knipling has emphasized it for entomo- 
logical practice in general (70). Let us, then, remember that toxicity can be measured for 
a compound in terms of grams or ounces, but the hazard of its use depends entirely upon 
the manner in which it is used. 
There is a natural tendency to emphasize the relative toxicity of an insecticide rather 
than its relative hazard. Aspray thatis toxic at 0.1 percent appears to be more dangerous 
than one toxic at 1.0 percent. In practice, this must be correlated with the concentration 
usually employed. For example, if the more toxic compound is used at 0.025 percent 
and the less toxic at 0.5 percent, the less toxic compound represents the greater hazard 
because a twofold increase would produce poisoning, while a fourfold increase would 
be required for the more toxic material. 
In the same manner, forage treated with 0.1 pound of insecticide producing toxicity 
in cattle at 10 mg./kg. is less hazardous than one applied at 4 pounds per acre with 
toxicity to cattle at 100 mg./kg. 
135 
