The control of parasites by grazing management

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Abstract
Among the most important of the parasites of grazing animals are the nematodes inhabiting the alimentary tract of the sheep. The losses due to the presence of these worms are difficult to estimate but are certainly not confined to the results of disease outbreaks. In fact, recent research (Tayler, 1953; Spedding, 1953) has emphasised the losses which occur at sub-clinical levels of infestation, that is, at levels sustained by normal sheep. Control of these parasites may be either ameliorative or preventive in character. Supplementary feeding and the use of anthelmintic drugs are of the former type; grazing management is essentially preventive. For the most part, anthelmintic drugs are now capable of preventing the outbreak of clinical disease, but they allow the presence of sub-clinical levels of infestation, as do most types of grazing management.