INFECTIOUS DISEASES OF CATTLE. 



495 



Cotton^ obtained at Knoxville, Tenn., records for September and 

 April somewhat longer than those given above. They are as follows: 



Cattle removed April 15 ; pasture free of ticks November 13. 



Cattle removed September 15 ; pasture free of ticks July 18. 



In localities with temperature and other conditions sunilar to those 

 at Knoxville, Tenn., these periods should be followed. 



TiTne required to render cattle free of ticks when placed on unin- 

 fested fields. — Before discussing plans for rendering farms tick free, 

 involving the use of the information given in the foregoing table, it 

 will be necessary to indicate how animals may be entirely freed from 

 ticks by placing them on uninfested fields. This is based on the fact 

 that the female tick must drop from the host to the ground before 

 eggs can be laid and before young ticks will develop. 



The shortest time in which seed ticks will appear after engorged 

 females have been dropped is 20 days. Consequently cattle placed 

 on a tick-free field during the warmer part of the year are not in 

 danger of becoming infested again with young ticks until 20 days 

 have elapsed. The time required for all the ticks to drop after cattle 

 have been placed on uninfested land varies with the temperature. 

 It is much longer during the winter than during the summer. The 

 time required, beginning at various times of the year, is given in the 

 following table : 



Time required for all ticks to drop from cattle placed on tick-free land. 



Freeing cattle of ticks hy rotation on tick-free land. — The plan of 

 freeing cattle of ticks by rotating them from one lot or field to an- 

 other is as follows : Beginning at any time of the year from February 

 to September, inclusive, the cattle are removed from the tick-infested 

 pasture they have been occupying to a tick- free lot or field, and con- 

 tinued there for not more than 20 days. During this time a con- 

 siderable number of ticks will drop. In order to prevent the cattle 

 from becoming reinfested (by seed ticks resulting from eggs laid by 

 females that have dropped), the herd is then changed to a second 

 tick- free inclosure for 20 days longer, and if they are not free of 

 ticks by that time they are placed in a third tick-free inclosure for 

 20 days more. Should the two changes at intervals of 20 days have 



1 Bulletin 81, Agricultural Experiment Station of the University of Tennessee. 



