Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Veterinary and Biomedical Sciences

First Advisor

Michael Hildreth

Second Advisor

Larry Holler


Haemonchus contortus is a common economically important gastrointestinal nematode that obliges the survival and productivity of small ruminants, especially sheep and goats. Anthelmintic resistance is a primary challenge in ruminant health management programs in preventing and controlling the H. contortus populations; therefore, there is a great necessity in finding and developing natural plant products for use as alternatives to commercial anthelmintics for controlling H. contortus in pastured sheep and goats. This dissertation has three major aims conducted in three separate studies: the first in vivo one was to evaluate the extended effect of a springtime, combined-treatment with 3 anthelmintics having different mechanism of action including moxidectin (Cydectin®), albendazole (Valbazen®), and levamisole (all given orally); this project was also coupled with a rotational grazing program on egg shedding in the United States Northern Great Plains flock of ewes whose H. contortus population showed benzimidazole and avermectin resistance. The results of fecal egg counts (FECs) 2 weeks before and after the treatment for 250 ewes showed a 99.99% FEC reduction from 3650 eggs per gram (EPG) to 0.17 EPG. The egg output remained very low until 10 weeks on paddocks. Output peaked on the 16th week at 42.1 EPG. During the following year, mean spring FEC was only 66.1 EPG and only 5.1 for the fall. Unfortunately, by the spring of 2016 egg output had increased to 1116.0 and remained high in 2017. The second study was an in vitro project aimed to measure the anthelmintic activity of Melilotus alba (white sweet clover) on H. contortus. The anthelmintic activity of methanol extracts from different sweet clover plant parts (i.e. leaves, stems, pods) were measured using a larval migration assay involving unsheathed third-stage H. contortus juveniles (J3). Stems and pods showed no anthelmintic activity, while 97.3% migration inhibition was measured in the leaf-extract at 30 mg/ml. An aqueous extract of the leaves (concentration of 670 mg/ml water) inhibited migration by 98% after 24 hrs., and no motility was observed after 48 hrs. Inhibition was higher at an acidic pH (e.g. pH of 3 and 5) than at a neutral pH (e.g. 7.4). Cytotoxicity of the aqueous leaf-extract was measured with unpolarized bovine ileal epithelial cells at 5 differing concentrations of the extract using an absorbance-based AlamarBlue assay. This assay showed that the extracts were vey toxic (100% cytotoxicity) at high concentrations. The goal of the third study was to evaluate M. alba anthelmintic effect on H. contortus under in vivo conditions. The experimental yearling ewes naturally and heavily infected with H. contortus were fed 0.68 kg of fresh-frozen M. alba (white sweet clover) (harvested from local plants in late fall) per day for 2 weeks. FECs were determined daily after the 2 weeks to estimate the post-treatment worm loads. Under these conditions, the results did not show any decrease in egg shedding, no significant effect (p > 0.05), within either experimental groups compared to the controls, but it showed an unexpected significant rise in egg output during the treatment period. The findings of these three studies suggest that the hypobiotic fourth-stage juveniles is the major cause of the rapid massive increase in H. contortus in spring; therefore keeping the animals inside the barns for a full year and applying a combined triple treatment while the animals are still inside the barns might help in the eradication of the arresting J4, then the next step is to run FECs next spring, and if the results showed no evidence of haemonchosis, then the animals could be released to the pasture using a rotational grazing system. Since the M. alba leaf-extracts showed signs of cytotoxicity to the unpolarized cells, this evidence should be investigated deeply using polarized intestinal cell lines and high doses of leaves should be given to experimental animals. If the future testing of white sweat clover extracts revealed no sign of toxicity, drenches of concentrated leafextracts and/or first-year plants containing mostly leaves could be fed to H. contortus infected sheep and goats. Such studies are encouraged to better evaluate the usefulness of feeding M. alba leaves.

Library of Congress Subject Headings

Sheep -- Parasites -- Control -- South Dakota.
Haemonchus contortus -- Control.
Nematodes -- Control.
White sweet clover.



Number of Pages



South Dakota State University



Rights Statement

In Copyright