PARASITES AND PARASITIC DISEASES OF HORSES 23 



From this account of the life cycle of these parasites it is evident 

 that horses infested with blood strongyles contaminate the pastures 

 on which they feed with the eggs produced by the worms, and that 

 the larvae which issue from the eggs and develop to the infective 

 stage may be swallowed by these and other horses. When horses 

 are kept on the same pastures year after year the number of eggs 

 and larvae gradually increases, and this contamination, accumulating 



Figure 15. — Section through the wall of the large gut, showing the head end of an 

 attached blood strongyle, 5". equinus, with a tuft of the inner lining of gut drawn 

 into the mouth cup of the worm. Greatly enlarged. From Wetzel, 1928. 



from year to year on a given pasture, may be highly damaging to 

 horses which are grazed there. Foals, in particular, suffer from the 

 effects of gross parasitism acquired in this manner. 



Symptoms and lesions. — The blood strongyles injure the wall of the 

 gut to which they are attached. These worms suck a tuft of the inner 

 wall of the gut into their mouth cups (fig. 15) and abstract blood from 

 this delicate lining. As the worms move from one place to another 

 within the gut they expose its injured wall to the entrance of disease- 

 producing bacteria. Bloodworms abstract blood from the finer blood 

 vessels in the lining of the gut, and when many worms are present in 



