Haemonchus, Trichostrongylus, Ostertagia and Nematodirus worm populations of sheep based on differential
egg counts are considered in relation to climatological and topographical data. Late spring, summer and early
autumn rainfalls are related to ground slope to assess wetness. Egg counts indicated that the estimated worm
populations in animals in flat areas with low rainfall were as heavy as or heavier than in animals on steep hilly
areas with a high rainfall. It is proposed that tactical anthelmintic treatment be based on the degree of wetness of
the grazing or farm.
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