With a few exceptions, the modern herbicides are of a relatively low order of toxicity, 
thus limiting the hazard of their use. 
A number of researchers have reported upon the toxicity of 2,4-D (2,4-dichloro- 
phenoxyacetic acid), 2,4,5-T (2,4,5-trichloro-phenoxyacetic acid), and their esters (38,53, 
63,77,107,108). The studies of Mitchell, et al, (1946) and of Grigsby and Farwell (1950), 
in which they grazed livestock on heavily treated pastures, indicate that the practical 
hazard with these materials is very low, Rowe and Hymas (1954) have studied 2,4,5-T by 
administering it to steers. 
At Kerrville, we have studied several herbicides in sheep and cattle. (Table 4). 
It is apparent that pentachlorophenol is one of the more toxic of these materials, 
producing poisoning in cattle and sheep in single doses of 25 mg./kg. Of this group, 
dinitro-o-sec-butyl phenol is the next most toxic, proving lethal for sheep after 4 daily 
doses of 25 mg./kg. Oddly, the alkanolamine salts of dinitro-o-sec-butyl phenol are 
much less toxic, one sheep having tolerated 35 daily doses of 25 mg./kg. each without 
showing symptoms. 
In general, the phenoxy-acid group of herbicides was of very low toxicity for sheep. 
The most toxic of this group was 2-(2,4,5-trichlorophenoxy) propionic acid in the form of 
propylene glycol butyl ether esters, 11 daily doses of 100 mg./kg. each producing death. 
This would still class it as a relatively nontoxic compound. 
The following materials were nontoxic when administered daily in 100 mg./kg. doses 
for 35 days: The alkanolamine salts of 2,4-dichlorophenoxyacetic acid and of 2-methyl- 
4-chlorophenoxyacetic acid, the propylene glycol butyl ether esters of 2,4-dichloro- 
phenoxyacetic acid and of 2,4,5-trichlorophenoxyacetic acid, the triethylamine salts of 
2,4,5-trichlorophenoxyacetic acid and the sodium salt of 2,2-dichloropropionic acid. 
The absence of poisoning from these materials administered in such high dosages 
for 5 weeks indicates that there is little hazard to livestock to be expected from normal 
usage. 
Dehydroabietylamine acetate (Delrad), an algaecide based upon technical abietal- 
amines, is used at very low rates in reservoirs and irrigation canals. Cattle and sheep 
were unharmed by consuming water treated with 100 p.p.m. Delrad, which is several 
times the concentration usually employed. This compound is extremely distasteful to 
cattle and sheep and probably would never be consumed by them voluntarily even if the 
chemical were left exposed. Cattle were unharmed by doses of 200 mg./kg., sheep by 
doses of 250 mg./kg. Higher doses produced poisoning. 
Because of the low toxicity and reduced hazard of herbicides, together with com- 
paratively restricted usage, the number of publications is small. Much of the evaluation 
of toxicity of these materials has been done with laboratory animals rather than with 
livestock, 
Reduction of Hazard by Control of Toxicity 
While very little can be done to change the specific toxicity of a pesticide, several 
things can be done to control it. 
There are certain compounds which may be administered simultaneously with the 
pesticide which antagonize its action directly or slow its action sufficiently to enable the 
organism to deal with it. 
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