BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE O 
methoxychlor. Sprays containing gamma benzene hexachloride ap- 
plied at 25 and 50 milligrams per square foot also gave good control 
for 2 to 6 weeks. However, lindane is not recommended for use on 
milk cows, and neither methoxychlor nor lindane should be applied 
to forage that is to be fed to dairy cows or to animals being fattened 
for slaughter. 
The Food and Drug Administration has stated that these new ma- 
terials would not be objectionable from a health standpoint if used 
according to recommendations. 
^Recommendations for the use of DDT to control insects on other 
livestock, including beef cattle, have not been changed. 
Effect of insecticides on livestock studied 
The toxicity of various insecticides and insecticidal formulations 
when applied to livestock was also studied. These studies included 
both acute toxicity resulting from single treatments and the possible 
chronic effects due to repeated applications for insect control. 
Young calves were found to be much more susceptible to acute 
poisoning than older cattle. However, little difference in suscept- 
ibility was noted between the young and old of swine, sheep, or goats. 
Single treatments with spray containing 1 percent of toxaphene or 
chlordane caused death or toxic symptoms in a small percentage of 
calves less than 6 weeks old. Benzene hexachloride at concentrations 
of the gamma isomer as low as 0.05 percent also affected some calves. 
Cattle a year or older tolerated at least four times the concentrations 
of these insecticides. Neither calves nor mature cattle showed toxic 
symptoms when treated with DDT, methoxychlor, or TDE in wettable- 
powder sprays containing 8 percent of the insecticide. 
To determine the effect on animals treated repeatedly with insecti- 
cides, several young steers and heifers 6 to 9 months old were sprayed, 
at intervals of 2 weeks, with emulsions containing 0.5 percent of toxa- 
phene or chlordane or sufficient technical benzene hexachloride to give 
0.025 percent of the gamma isomer. After 12 applications all the 
treated animals showed gains in weight at least equal to those in un- 
treated check animals. These preliminary studies indicate that none 
of these insecticides when used for insect control are likely to have 
any adverse effect on the growth of cattle. 
Storage of insecticides in fatty tissues of cattle 
Several experiments were conducted to determine the extent to which 
insecticides are stored in the fatty tissue of cattle. In one experiment 
two groups of four Hereford cows were sprayed five times at 28-day 
intervals with 0.5 percent of DDT, a wettable-powder spray being 
used on one group and an emulsion on the other. Each of the cows 
was suckling a calf, but only two of the calves in each group were 
sprayed. One month after the last spraying, all the animals were 
slaughtered and samples of the fat were analyzed for DDT content. 
The fat from the cows treated with the emulsion spray showed an 
average of 15.2 parts per million, and from those receiving the wet- 
table-powder spray 14.6 parts per million. The fat from the treated 
calves averaged 52 parts per million, whereas that of untreated calves 
suckling on treated cows showed 25 parts per million. 
