DISEASES OF SHEEP 583 



divisions of large pastures, and in many instances could not be profit- 

 ably employed, but in cases where it could be used it would undoubt- 

 edly prove very effective. By the time the next lamb crop appeared 

 the pastures used the year before would have remained vacant long 

 enough for the infection to have disappeared, and would conse- 

 quently again be ready for use. By continuing this rotation from 

 year to year, not only would each crop of lambs be protected from 

 infection, but as reinfection of the infested ewe flock is prevented at 

 the same time, the parasite w r ould in a few years be entirely eradi- 

 cated from the flock and pastures. 



If such frequent rotation is not possible or practicable, a smaller 

 number of pastures may be utilized, after the ewe flock has been 

 treated with vermifuges. The treatment may be given either before 

 or after the birth of the lambs. If before, the ewes should be treated 

 before pregnancy is too far advanced, in order to avoid possible bad 

 results from the handling necessary in treatment. Probably the best 

 time for treatment is late in the fall or early in the winter. The 

 treated sheep should be placed immediately on clean pasture in order 

 to avoid reinfection. The object of treating the ewes is to get rid of 

 the worms w T ith which they are infested, and thus remove the source 

 from which the pasture becomes contaminated. If it were possible 

 by treatment to free the old sheep entirely from stomach worms, it 

 is evident that the lambs would remain free from infection, provided^ 

 of course, that the flock were afterwards kept on clean pasture. 

 Unfortunately, there is no vermifuge known which can always be 

 depended upon to remove all of the worms, but it is possible to get 

 rid of most of them and thus greatly reduce the amount of infection 

 to which the lambs will be exposed. Two other methods may be sug- 

 gested by which lambs can be kept free from infection with stomach 

 worms. 



1. It is assumed that a large pasture is available which has had 

 no sheep, goats, or cattle upon it for a year, if a permanent pasture, 

 or since cultivation, if a seeded pasture. This pasture is subdivided 

 into two by a double line of fence, and a drainage ditch is run along 

 the alley between the two fences. At one end of the alley between 

 the two subdivisions a small yard is constructed, communicating 

 with each of the subdivisions by means of a gate. When the lambs 

 are born they are placed in one of the subdivisions and the ewes are 

 placed in the other. The small yard should be kept free of vegeta- 

 tion and must not drain into the lamb pasture. As often as neces- 

 sary the lambs are allowed in the small yard with the ewes for suck- 

 ling. The rest of the time the lambs and ewes are kept separate in 

 their respective pastures. By this arrangement the lamibs are ex- 

 posed to infection only while they are in the small yard, where they 

 may become infected either by embryos of the stomach w r orm pres- 

 ent on the manure-soiled skin of the infested ewes, or by embryos 

 picked up from the ground which has been contaminated by the 

 droppings of the ewes. The chances of infection from the skin of 

 the ewe are so slight that in practice this source of infection need not 

 be considered. The danger of infection from the ground may be 



