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ISSUED NOVEMBER, 1930 
REVISED JANUARY, 1933 
UNITED STATES DEPARTMENT OF AGRICULTURE 
WASHINGTON, D. C. 
CIRCULAR No. 148 
PARASITES AND PARASITIC DISEASES OF HORSES’ 
By BENJAMIN ScHWARTzZ, Senior Zoologist, MARIon IMEsS, Senior Veterinarian, 
and WILLARD H. WricuT, Associate Veterinarian, Zoological Division, Bureau 
of Animal Industry 
CONTENTS 
- Page Page 
Internalsparasites Ol NOrses=sasen eee 1 | Internal parasites of horses—Continued. 
Abundance and location_________________ 1 DIS DOSALVO fad AMULET Sere nee eee 31 
Symptoms and damage produced by Summary of control measures____________ 32 
DATASILCS ae tie ke eS hy PA ae ee 1 | External parasites of horses__________________ 34 
General control measures________________ 2 EORsepliceesss 2 ae P18, iN ae 34 
Medremalitredtim ents ne ee 3 FEV OUSC SINT) FC ees Ss area eee eee 38 
IETOCLOZOd kas Sree Ses) as yee eae 4 BURT CK Que = cB E Aces Us MA pr ReGen eat ee es at 45 
or DATASITES ee oe oe 4 Treating horses for external parasites__- 48 
OLS ee es irs at ees ASO RSS ct 29 
INTERNAL PARASITES OF HORSES? 
ABUNDANCE AND LOCATION 
HE 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. Al 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 cf 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, 
153249°—33 1 
