18 



CIRCULAR 11 



U. S. DEPARTMENT OF AGRICULTURE 



These parasites multiply very rapidly, the entire development on 

 the ground taking place in a few days. The infective larvae, whether 

 they hatched from the eggs eliminated with the feces or from the 

 eggs produced by the free-living generation of worms, are taken in 

 by horses with food and are also capable of penetrating the intact 

 skin. Within about two weeks after the larva? have been taken up 

 by horses they have developed into mature females which soon begin 

 to discharge eggs into the intestine of the host. 



Symptoms and lesions. — While no definite symptoms have been 

 described in horses as resulting from infestation with these parasites, 



the worms are prob- 

 ably responsible for 

 diarrhea in foals. 

 These worms make 

 their appearance in 

 foals earlier than do 

 other parasites, and 

 the infestation tends 

 to become heavy as a 

 result of reinfesta- 

 tions which may take 

 p la c e rapidly and 

 often, because of the 

 brief period required 

 for development out- 

 side of the host. The 

 parasites are usually 

 embedded in the lin- 

 ing of the intestine 

 and doubtless produce 

 considerable i r r i t a- 

 tion. The fact that 

 the infective larva? 

 are capable of pene- 

 trating the skin adds 

 another complication 

 and it is probable that 

 foals acquire part of 

 their infestation while 

 tying down on pas- 

 tures and in their 

 stalls. As the larvae 

 penetrate the skin it 

 becomes reddened and obscure skin troubles in horses may be caused 

 by the penetration of these worms. The larval worms may carry 

 pathogenic bacteria into and through the skin. 



Treatment. — Nothing is known concerning effective treatment for 

 these threadworms. In severe cases of diarrhea, in foals, caused by 

 this parasite, carbon tetrachloride is worthy of trial. The drug may 

 be used for foals at a dose rate of 0.1 cubic centimeter per kilogram 

 (2.2 pounds) of body weight or 10 cubic centimeters (2.5 fluid drams) 

 for a 220-pound animal. In order to remove the bulk of ingesta in 

 the small intestine and render the parasites more accessible to treat- 

 ment, it is advisable to administer a purgative 24 hours before treat- 





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Figure 11. — Type of sanitary box stall. Note feed "box 

 and hayrack raised above the ground 



