338 SANITARY ENTOMOLOGY 



pyrethrum. These are not recommended. Cattle lice are too difficult to 

 control for such methods to be effective. 



TIME FOR THE APPLICATION OF CONTROL MEASURES 



Though cows are infested with the largest numbers of cattle lice 

 during the months of January and February, yet the measures for their 

 control should be applied long before that time; in fact, they should be 

 used within a week after they have been brought into the barn for the 

 fall and winter. A second application should follow twelve or thirteen 

 days afterward. The purpose of these two applications is to rid the 

 cows of the lice that are on them before they become numerous and 

 spread to more susceptible animals. The lice may not be seen at this 

 time but the dairymen should not reason that the lice are not present. 

 This gives a proper length of time for all of the three species of cattle lice 

 to hatch from eggs, but not long enough for them to lay eggs again and be 

 in a resistant stage where the treatment will not reach them. 



Treatment should be repeated at intervals of a month from the 

 second treatment. In case animals show any great number of lice, 

 treatment should be given and repeated in twelve or thirteen days. 



Treatment with linseed oil can be made at the usual time when the 

 cows are being groomed and cleaned. 



From five to six treatments during the fall and winter should control 

 the lice in the average herd. 



SKIN INJURIES 



One of the most troublesome phases of the study of the control of 

 cattle lice was to determine the strength of insecticides that would kill 

 the lice but would not injure the skin, thus causing the hair to come out 

 badly or making distinct burns. 



The skin of the cow is very susceptible to injury when compared 

 with the skin of other animals. It is known that cows have been killed by 

 the application of certain insecticides recommended for the control of 

 cattle lice. This indicates that caution must be taken in the use of control 

 measures that have not been sufficiently tested. Caustic washes cannot 

 be used without danger of their doing considerable injury, unless they 

 are very accurately measured and applied very carefully to the skin of 

 the animal. 



It is known that exposure to direct sunlight and active exercise after 

 ■application contributes to cause shin injury with nearly every one of the 

 control measures for cattle lice. 



It is doubtful if there is any application that will kill lice on cows 



