BUREAU OF ENTOMOLOGY AXD PLAXT QUARANTINE 35 
dielclrin was tolerated by yearlings with no toxic effects. Repeated 
applications of a 0.5-percent spray at 2- and 3-week intervals pro- 
duced toxic effects but no deaths. Application of sprays containing 
0.25 percent of dieldrin on eight beef animals at 3-week intervals had 
no apparent toxic effects. Comparable data on other insecticides in- 
dicate that dieldrin as a spray is at least four times as toxic as chlor- 
dane or toxaphene to young calves and from one-half to one-fifth as 
toxic as the gamma isomer of benzene hexachloride. 
Fat of Sprayed Livestock Tested for Presence of Insecticides 
Investigations were continued to determine the extent to which in- 
secticides applied repeatedly for controlling livestock pests or con- 
sumed as residues on feeds are stored in the fat of cattle. 
Of special importance was the observation that animals sprayed at 
3-week intervals reached the maximum storage of insecticide after 
two or three treatments. Thereafter the rate of storage and elimina- 
tion of the insecticide reached equilibrium. 
DDT was applied as a 0.5-percent emulsion spray to cattle at inter- 
vals of 2 weeks. Biopsv samples of fat taken from the animals showed 
that after 28 to 36 treatments the DDT content of the fat of 12 ani- 
mals averaged approximately 85 p. p. m. (parts per million). No 
harmful effects of the DDT treatments were apparent. The animals 
showed weight gains equal to those of untreated control animals. 
As a 2-week treatment schedule with DDT is not standard practice 
in livestock-pest control, a similar experiment was conducted follow- 
ing the usual 3-week schedule. After six treatments the fat from the 
animals averaged about 35 p. p. m. of DDT. TDE in a similar ex- 
periment gave similar results. 
The application of sprays containing 0.03 percent of lindane to 
cattle at 3-week intervals caused no detectable storage of lindane in 
fat of the animals. Cattle treated at 3-week intervals with 0.5 percent 
methoxychlor sprays showed only 2.4 p. p. m. of methoxychlor in fat 
following six applications. 
Dieldrin applied as a 0.05-percent wettable-powder spray resulted 
in increases of organic chloride in the fat equivalent to 24 p. p. m. of 
the insecticide after three treatments at 3-week intervals. 
A single treatment of cattle with 0.5-percent chlordane sprays 
caused no significant increase of organic chlorides in the fat. Single 
treatments with DDT resulted in deposition of about 11 p. p. m. in 
the fat. Similar results were obtained with TDE. 
Beef cattle given a diet containing 10 p. p. m. of methoxychlor 
showed no detectable methoxychlor in the fat 30 days after feeding 
began. Similarly, beef cattle showed no significant increase in organic 
chlorides in the fat following 30 days on a diet containing 10 p. p. m. 
of toxaphene. 
Two beef animals and two sheep kept for 2 months on a diet con- 
taining 25 p. p. m. of chlordane showed an increase in organic chlo- 
rides in the fat equivalent to about 16 p. p. m. of chlordane in cattle 
and 11 p. p. m. in sheep. A like group of animals on a diet containing 
25 p. p. m. of aldrin showed an increase of organic chlorides equivalent 
to 78 p. p. m. of aldrin in both the cattle and sheep. Similar results 
were obtained with dieldrin. 
