TABLE 1.--Maximum cholinesterase inhibition due to administration of several systemic 
insecticides to cattle. 
Insecticide Method of Maximum ChE 
ier) inhibition Bc a 
Ronnel: Percent 
100 Oral bys) 21 
100 do. 40 2A 
Co-Ral: 
40 Dermal 40 14 
by2 do. 42 25 
37 do. 36 25 
Dimethoate: 
10 Oral S69 als} 
10 Intramuscular A2 als} 
Cyl) Oral 40 4 
40 do. 80 4 
Ruelene: 
aay Intramuscular 2A 22 
40 Dermal 25 6 
present in blood provide information as to how fast the insecticide and its metabolites 
are absorbed by the animal. In addition, the radioactivity can be fractionated into 
insecticide, oxidation products, and hydrolysis products to find out how long the unchanged 
compound is present, what levels it reaches, and when all the insecticide is gone, The 
rate at which these changes occur is related to the solubility of the compound and to 
the ease with which it is detoxified by the animal. 
Further information can be gained by bioassaying samples of the blood, The blood 
of treated animals may be fed to stableflies and the toxicity compared with the results 
obtained by radiometric analyses (Kaplanis, et al. 1956). The use of bioassay techniques 
on blood is especially valuable in determining the possibility that the animal might 
convert the compound to a more toxic material (Roberts, et al. 1958). The formation 
of such a material--for example, the oxygen analog of a phosphorothioate insecticide -- 
has been demonstrated with several systemics. Data onpeak levels of several insecticides 
in the blood of treated animals are summarized in table 2. 
Milk.--An important consideration in the development of systemic insecticides is 
the nature of residues in the milk of treated animals. Compounds that are not secreted 
in milk could be used to treat lactating dairy animals. All the systemic insecticides 
tested thus far on dairy animals at dosages that control cattle grubs have been found 
in milk samples taken shortly after treatment. Because of this finding, no systemic 
insecticide is presently recommended for use on lactating dairy animals. Data on 
residues in milk are summarized in table 3, 
Excretory Products,--An insecticide fed to animals can either be stored as such or 
as an oxidized derivative, or it can be detoxified and excreted, It is now known that 
almost all the phosphorus insecticides are rapidly brokendown and excreted by mammals, 
Examination of excretory products of treated animals has shown the rate of excre- 
tion to vary greatly--from almost complete elimination within a few hours of treatment 
with some compounds to elimination over a period of weeks with others. This variation 
is affected by a number of factors, among which ease of absorption, solubility, sus- 
ceptibility to hydrolysis, and route of administration are known to be important. Radio- 
activity in excretory products may reach very high levels. 
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