Studies on the epizootiology ofNematodirusinfestation in sheep in New Zealand

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Abstract
Epizootiological studies over a three-year period have shown a remarkable regularity in the occurrence and course of Nematodirus infestation in lambs. Observations of larval populations on pasture have shown the presence of a small larval peak in the spring followed by a larger peak in the autumn. A trial conducted in the autumn of 1959 has shown the importance of the autumn larval peak with regard to susceptible animals. Differences were found to occur in the duration of spring- and autumn-acquired infestations, and evidence is presented indicating that older sheep do possess some measure of 2ge resistance to Nematodirus infestation.