26 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE 
or Cylicostomum, are usually about a half inch or less in length and 
grayish white in color, and occur attached to the gut wall or free in 
the contents of the large intestine of the horse. These worms do not 
feed on blood, at least ordinarily, but they may feed on the mucosa 
of the large intestine. The immature forms of some cylicostomes 
occur in nodules in the wall of the large intestine. 
The small strongyles of the horse contribute to the picture of gross 
parasitism, and together with the large strongyles, are responsible for 
digestive disturbances, weakness, emaciation, and anemia resulting 
from severe infestations with parasites. 
The life histories of the smaller strongyles have not been studied 
in detail, but the indicated control measures with reference to these 
worms are the same as those recommended in connection with the 
control of blood strongyles. 
FicurE 19.—Lesions produced by one of the smaller horse strongyles: A, enlarged 
view of lesion with worms, Triodontophorus tenwicollis, surrounding it; B, types 
of lesions. (From Ransom and Hadwen, 1918) 
Treatment.—The treatments recommended for the removal of large 
strongyles are also used for the removal of small strongyles. Oil of 
chenopodium and normal butylidene chloride are especially effective 
against these worms. Carbon tetrachloride is less effective. 
PINWORMS 
The pinworms, Owyuris equi, which are commonly seen in horses 
are the females. These are relatively long, whitish worms with a 
very long and slender tail. (Fig. 20.) The males are small and 
inconspicuous and are seldom found. The females may attain a 
length of 3 to 6 inches. They occur in the large bowel. 
Life history—The gravid females pass out with the manure and 
then deposit their eggs, instead of depositing them in the bowel. 
Sometimes the females hang on to the anal opening and extrude their 
eggs in the region around the anus; the eggs may adhere in this 
