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'Trichostrongylus colubriformis' and 'T. vitrinus' are nematodes infecting the small intestine of ruminants, mainly sheep and goats. These species are closely related and can occur simultaneously in the same host. Despite such similarities anecdotal evidence suggests proportions of these two species tend to vary greatly between regions, between paddocks in the same region and between sheep in the same paddock. Of the two species, 'T. vitrinus' is known to be more pathogenic making it desirable to know what influences differences in species proportion to possibly manipulate the environment and, therefore, species proportion, or to more accurately predict abundance of 'T. vitrinus'. Factors considered were; anthelmintic treatment, host nutrition, host resistance status, interspecific competition and temperature. In order to study factors affecting species proportion a reliable method of species identification was necessary to distinguish between the eggs, larvae and females of the two species. A variety of possible techniques were reviewed before a DNA based species identification technique, using the second internal transcribed spacer of ribosomal DNA, was chosen. To investigate effects of anthelmintic treatment on species proportion, experiments were conducted on nematode populations from two properties. This work showed that after exposure to a range of anthelmintics, 'T. colubriformis' and 'T. vitrinus' can develop different levels of resistance to these anthelmintics. Results also confirmed that species proportion varied significantly between regions and between sheep in the same paddock. |
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