CIRCULAR No. 148 



Issued November, 1930; Revised January, 1933; Slightly revised May, 1934 



UNITED STATES DEPARTMENT OF AGRICULTURE 



WASHINGTON, D. C. 



PARASITES AND PARASITIC DISEASES OF HORSES 1 



By Benjamin Schwartz, Senior Zoologist, Marion Imes, Senior Veterinarian, 

 and Willard H. Wright, Associate Veterinarian, Zoological Division, Bureau 

 of Animal Industry 



CONTENTS 



Page 



Internal parasites of horses 1 



Abundance and location 1 



. Symptoms and damage produced by 



parasites 1 



General control measures 2 



Medicinal treatment 3 



Protozoa 4 



Worm parasites 4 



Bots 29 



Page 

 Internal parasites of horses— Continued. 



Disposal of manure 31 



Summary of control measures 32 



External parasites of horses 34 



Horse lice 34 



Horse mange 38 



Ticks 45 



Treating horses for external parasites... 48 



INTERNAL PARASITES OF HORSES 2 



ABUNDANCE AND LOCATION 



THE TERM PARASITE as used in this circular refers to forms 

 of animal life which, for the purpose of obtaining food and 

 shelter, live on or in the bodies of other animals which are larger 

 than the parasites and are known as hosts. All classes of domesti- 

 cated animals harbor numerous kinds of parasites, and horses, in 

 particular, are liable to infestation not only with many different 

 kinds but also with very large numbers of these pests. A horse's 

 stomach may contain hundreds of bots, and the small intestine may 

 be packed with large roundworms. The large intestine of the horse 

 is a location especially preferred by parasites, and very often the 

 colon and cecum are found to be teeming with hundreds or thousands 

 of wriggling, parasitic worms, some free in the lumen and others 

 attached to the walls of the gut. Several kinds of worm parasites 

 present in the gut and elsewhere have previously wandered through 

 various parts of the horse's body before reaching their final locations. 

 In fact, there is hardly an organ or a tissue in the horse which is 

 absolutely free from possible attacks by mature parasites or by their 

 wandering larval forms. 



SYMPTOMS AND DAMAGE PRODUCED BY PARASITES 



Parasitic diseases, unlike diseases caused by bacteria, are seldom 

 spectacular in their onset and symptoms and are marked by a slowly 



1 This circular supersedes Farmers' Bulletin No. 1493, Lice, Mange, and Ticks of Horses. 



2 By Benjamin Schwartz and Willard H. Wright. Many of the illustrations in thia 

 section of the circular were drawn by Joseph E. Alicata, junior zoologist. 



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