CIRCULAR No. 148 
Issued November 1930; revised January 1933; slightly revised January 1936 
UNITED STATES DEPARTMENT OF AGRICULTURE 
WASHINGTON, D.C. 
PARASITES AND PARASITIC DISEASES OF HORSES' 
By BENJAMIN SCHWARTZ, Senior Zoologist, MARIon IMES, Senior Veterinarian, 
‘ and WILLARD H. WricHT, Associate Veterinarian, Zoological Division, Bureau 
of Animal Industry 
CONTENTS 
Page Page 
Internal parasites of horses.....-....-.----_- 1 | Internal parasites of horses—Continued. 
Abundance and location_____-_-_----_--__ 1 Misposaliof mantresas see sees esse ee 31 
Symptoms and damage produced by Summary of control measures_____.______ 32 
DATASET CSE se ete wi a ie is es Ba te 1 | External parasites of horses__________-______- 34 
General control measures__________---__- 2 IFLOTSE ICO ws Met A Ne RIS Ey ie ee 34 
Medicinal'treatmentie ase 522 oe eee 3 IFLOTVSe Manse se eee ee eee ete 38 
IP ROCOZ OD eee ea Rats eee cesta 4 ARKO) 5) HERO aie Ot ean enema TE Tae 45 
WOLD AaLasites es ase ee ane eee 5 Treating horses for external parasites__- 48 
CO eR rr ys ie Or a et 
INTERNAL PARASITES OF HORSES? 
ABUNDANCE AND LOCATION 
HE TERM PARASITE as used in this circular refers to forms 
4 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. 
* By Benjamin Schwartz and Willard H. Wright. Many of the illustrations in this 
section of the circular were drawn by Joseph E. Alicata, junior zoologist. 
138442 °—37 a 
