4 Farmers’ Bulletin 1150. 
are more easily infected by parasites than older ones, although very 
old sheep sometimes appear to acquire an increased susceptibility to 
infection.. Hence it is important in undertaking to prevent infesta- 
tion with parasites to pay especial attention to the care and handling 
of lambs and yearlings. 
IMPORTANT PREVENTIVE MEASURES. 
The use of measures intended to prevent sheep from becoming 
infested with parasites is especially the function of the sheepman. 
When sheep become diseased, the niceties of diagnosis and the ad- 
ministration of drugs are well within the province of the veteri- 
narian. Errors in diagnosis by unskilled persons waste valuable time 
and lead to useless or injurious measures. Drugs intended to kill 
parasites are from the nature of things usually very potent, and 
are commonly poisonous substances capable of doing much damage 
in the hands of unskilled or careless persons; therefore, it is usually 
advisable to secure the services of a competent veterinarian whenever 
there is an outbreak of disease and a good veterinarian is available. 
In places where there are no qualified veterinarians available, the 
farmer or stockman must use his own judgment in determining 
whether he can recognize the trouble and administer the remedy. 
One of the most important preventive measures in keeping flocks 
free from parasites is based on the fact that many of the sheep para- 
sites live in the digestive tract of the sheep or in organs in commu- 
nication with the digestive tract, so that the eggs or young worms 
pass out in the manure and thus infect the pastures.. The fact that 
sheep manure carries worm infestation is the basis of such preven- 
tive measures as pasture rotation, rotation of different kinds of 
stock on the same pasture. feeding from racks or board floors, use 
of bare lots for nursing lambs, etc. 
Another important preventive measure is based on the fact that 
many parasites which do not get back to the sheep from a pasture 
infected with sheep manure are carried back to the sheep by dogs. 
The fact that the dog which feeds on uncooked sheep meat or viscera 
may become infested with worms that produce eggs which pass out 
on to the pastures and may then infect the sheep, is the reason for 
keeping sheep dogs and other dogs on the farm free from worms and 
related parasites and for insisting that stray dogs must not wander 
over pastures and fields under penalty of being shot. Another pre- 
ventive measure is based on the fact that diseases like scab are trans- 
mitted by contact with infected animals and places, and clean flocks 
must be protected from unsafe contacts. 
In a general way, the presence of parasites may be suspected as the 
cause of disease where there is little or no fever, the animals losing 
