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Title: The role of condensed tannins towards ovine nematodes and their consequences on host performance
Author: Athanasiadou, Spiridoula Georgiou
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2001
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The aim of this thesis was to investigate the two hypotheses that have been put forward to account for the reduction in the level of parasitism observed in sheep that consume condensed tannins. For this purpose in vitro (larval development/viability assay) and in vivo experiments were performed. In the first two experiments, a model condensed tannin extract (Quebracho) was given as a drench to parasitised sheep to test for the direct effect of condensed tannins towards established adult nematodes. Experiment 1 aimed to provide evidence for a direct anthlemintic effect of condensed tannins towards an established Trichostrongylus population. For this purpose the extract was administered to sheep four weeks after their initial infection. There was clear evidence for a direct anthelmintic effect of condensed tannins towards adult T.colubriformis, as demonstrated by reduced faecal egg counts and worm burdens. As T.colubriformis is an intestinal ovine nematode, the susceptibility of other intestinal and abomasal ovine nematodes to condensed tannins was investigated in vitro and in vivo. In vitro larval development/viability assays were performed to test the effects of different concentrations of Quebracho extract on pre-parasitic larval stages of one intestinal (Trichostrongylus vitrinus) and two abomasal nematodes (Teladorsagia circumcincta and Haemonchus contortus) (Experiment 2a). The results from these assays showed that larvae from all species were able to develop to infective larvae, irrespectively the concentration of Quebracho extract. However, the viability of infective larvae of all species decreased as the concentration of condensed tannins increased. Concurrently, Experiment 2b was designed to test whether condensed tannins had a direct anthelmintic effect towards adult populations of either T. circumcincta or H. contortus, or towards a mixed intestinal population of Nematodirus battus and T.colubriformis. Both ovine intestinal species were susceptible to the presence of condensed tannins in the gastrointestinal tract of sheep, as demonstrated from reduced faecal egg counts and worm burdens.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available