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Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Biology and Microbiology

First Advisor

Michael B. Hildreth


Bison producers face many challenges, including the transmission of parasitic diseases such as trichostrongylosis and toxocariasis into and within their herds. These diseases can reduce animal production and cause occasional death. There have been no surveys to identify gastrointestinal nematodes common to bison herds. This study determined the prevalence and intensity of nematode infections within bison age-categories covering 31 herds from 8 northcentral U.S.A. states. This is also the first bison study using PCR to identify genera of trichostrongyles in fecal samples. This survey involved collecting fecal samples and a questionnaires from participating bison producers. Fecal egg counts were performed on 1235 fecal samples, and a PCR assay was performed on 150 DNA samples to determine the genera of trichostrongyles represented by these eggs. A comparative study was done on a bison herd from Flandreau, SD that was experiencing clinical parasitism. In July yearling samples from the Flandreau herd, prevalence was 85.7%, and the mean intensity was 28.2 EPG. This increased to 100% prevalence and an intensity of 124.7 EPG by August. In comparison, trichostrongyle prevalence among yearlings in the other 30 herds was 75.5% and their intensity was 23.0 EPG in samples collected mainly in May-July. Other parasites such as Moniezia, Nematodirus, Trichuris, and coccidians were also identified in these samples. The PCR assay, focused on the interspacial regions of rDNA to detect 4 trichostrongyle genera commonly present in cattle and sheep. They included Haemonchus, Ostertagia, Cooperia, and Trichostrongylus, and at least 1 of these genera were identified in virtually all samples tested. Cooperia and Haemonchus were found in most samples, and Ostertagia and Trichostrongylus were less common. Toxocara vitulorum was found in calves from 2 out of 12 Minnesota bison herds that aubmitted calf samples. Microscopy revealed novel egg-like structures resembling T. vitulorum eggs that were commonly present in fecal samples from bison of various ages, particularly in bison herds infected with T. vitulorum. The susceptibility of bison to gastrointestinal nematodes is more similar to cattle than of sheep, and co-grazing yearling bison with cow-calf pairs contribute greatly to the problems of trichostrongylosis in bison herds.

Library of Congress Subject Headings

American bison -- Parasites -- Great Plains.
Veterinary parasitology
Nematodes as carriers of disease.


Includes bibliographical references (pages 125-132)



Number of Pages



South Dakota State University


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