Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Biology and Microbiology

First Advisor

Ernest J. Hugghins


The American Association of Veterinary Parasitologists reported that nematodes in sheep represent an unquestionably great production loss, and that the absence of deworming on a routine basis would hamper modern sheep production. After ingestion, the infective third stage larva, or L3, exsheaths and burrows into the digestive glands, and becomes a fourth stage larva, or L4. According to Armour, 18 to 21 days after L3 ingestion occurs, the nematode reaches sexual maturity. However, while in the gastric glands, these L4 invade the parietal, or hydrochloric acid (HCl) secreting cells, damaging them, and replacing them with non-acid secreting cells. This leads to an increase in abomasal pH, and further problems: 1. Reduced pepsinogen activation to pepsin. 2. Failure to denature proteins. 3. Loss of "bacteriostatic effect." Armour also describes the subsequent permeability increase of the abomasal wall to pepsinogen. Dunn further points out that as a part of their normal, direct life cycle, the trichostrongylids use hypobiosis, or "arrested larval development" as an evolved survival mechanism. During periods of adverse climate, they merely halt at the L4 stage to overwinter in the abomasal glands. According to Armour, they resume development in the spring and reach sexual maturity within 14 to 17 days. The sudden presence of great numbers of mature nematodes is immediately followed by the presence of increased fecal egg counts. This phenomenon has acquired the name "spring rise." Armour has suggested that the "spring rise" may be. analogous to diapause in insects. Diapause is described by Highnam and Hill as being under hormonal control, but research in nematodes is hampered by anatomical dissimilarities as compared to insects. Recent tests for plasma pepsinogen levels have been implemented by researchers such as Armour and Thomas and Waller in an attempt to correlate the damage done to the abomasal mucosa by these nematodes in normal seasonal, and in long-term arrested development. Another practical application being pursued is to find a correlation between plasma pepsinogen levels and fecal egg counts. Campbell et al. describe the development of a strong new antiparasitic compound, Ivermectin, by MSD AGVET division of Merck and Co., Inc., Rahway, New Jersey, that is effective against these inhibited L4 trichostrongylid stages, especially Ostertagia. Levamisole HCl, manufactured by Pitman-Moore, Inc., Washington Crossing, New Jersey, was also used in one test to observe any increase in rate of weight gain. The primary objectives of this research were: 1. An evaluation of the advantages of worming based upon any significant increases in rate of weight gain in two different groups of lambs under quite different management conditions. 2. The inspection, at the slaughter of random test animals, of abomasal contents to determine nematode genera present. 3. The testing for plasma pepsinogen levels in blood samples according to the method outlined by Black, and the correlation of these to fecal egg counts.

Library of Congress Subject Headings

Sheep -- Diseases
Sheep -- Parasites
Cysticercus ovis



Number of Pages



South Dakota State University


No Copyright - United State