THE DISEASES OF SHEEP 337 



young worms, which are not killed by cold weather 

 after they have reached the final stage of larval 

 development. When they are weaned the lambs 

 must, of course, be placed on clean pasture, if they 

 are to continue free from infection. With this 

 method only two clean pastures are necessary, one 

 in which the ewes and lambs are placed in the fall, 

 and another for the lambs when they are weaned in 

 March. Thus started in life free from the chance of 

 infection, the shepherd may more surely count on 

 profit from his lambs. 



Fortunately for this scheme, it is always possible 

 to have lambs born early during the winter season; 

 and with additional clean pastures a modification 

 of the foregoing method may be used in the case 

 of lambs born toward the end of the winter or in 

 the spring. In the northern United States lambs 

 born the first of February for example, may be 

 kept with their mothers in a clean field or pasture 

 until the last of March, as in the case of those 

 born at the beginning of winter, but unlike the latter 

 they will not then be old enough to wean. Accord- 

 ingly they are not separated from the rest of the 

 flock, but the ewes and lambs are moved together 

 to a second clean pasture April 1. May 1 they are 

 moved to a third clean pasture, May 15 they are 

 moved again, and finally the lambs are weaned June 

 1 at the age of four months, and moved by them- 

 selves to a clean pasture. In the case of lambs 

 born the first of March and weaned the first of July 

 three additional clean pastures would be required 



