Some Recent Advances in the Epidemiology and Control of Helminth Infection in Sheep
نویسنده
چکیده
Recent studies on the free-living stages of gastro-intestinal worm parasites of sheep show that their rates of development to the infective stage is slower and the mortality of infective larvae in pastures is lower than was believed hitherto. This, together with findings on the natural regulation of worm populations in sheep,. suggests that worm burdens do not increase through a rapid succession of generations. Therefore, the concentration of free-living stages in pastures when susceptible animals begin to graze or at the beginning of periods favourable for parasite replication will have an important influence on the ultimate size of the worm burden. These concepts are exemplified by control measures for strictly winter-rainfall regions, based on drenching during the hot, dry summer when larval availability in pastures is very low. In accordance with the same principles, it is likely that practices adopted at weaning will be much more important in preventing production losses due to parasitism in young sheep than drenching ewes at lambing time. Preliminary findings suggest that drenching lambs at weaning and moving them to clean grazing can provide prolonged protection from parasitic disease independently of weather favourable for parasite transmission.
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