Observations on the Seasonal Variations in the Worm Burdens of Young Sheep in Southern Western Australia

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Abstract
Observations, limited to one year, on autumn born and spring born lambs and weaners indicated that very few infective larvae of bursate nematodes, with the exception of those of Nematodims spp., were ingested after the middle of spring, with the result that at least until they were eight months old, and probably older, spring born lambs were comparatively lightly infested.These observations also suggested that retarded larvae, especially the histotropic stages, are the cause of the “summer rise” in weaners and that they also cause the “parturition rise” in autumn lambing ewes, and can be the cause of increased worm egg production in wethers.It seems probable that the “summer rise” of sheep in the southern part of Western Australia is comparable to the “spring rise” of sheep in the United Kingdom and elsewhere.