The Significance of Winter Survival of Free-Living Stages on the Epidemiology of Nematodiasis: Its Effect in Connection with Set-Stocking and Alternate Grazing with Sheep and Cattle
The following gastro-intestinal nematodes are found in cattle in Norway; Ostertagia ostertagi, O. lyrate, Nematodirus helvetianus, N. battus, Cooperia oncophora, C. mcmasteri and Triehuris sp: species of the same genera also occur in Norwegian sheep. The grazing period for cattle is usually 4 – 5 months and parasites which are pasture transmitted must either survive winter as free-living stages on the pasture or in carrier animals. The free-living stages of all the common species of cattle nematodes are able to survive the winter in Norway, but with sheep the free-living stages of some of the nematodes show poor winter survival on the pasture. These include Haemonchus. contortus, Trichostrongylus spp, Cooperia curticei, Bunostomum trigonocephalum and Oesophagostomum venulosum. Cattle can also be infected with species of the genera Haemonchus, Trichostrongylus, Bunostomum and Oesophagostomum, but the absence of these nematodes from cattle in Norway may be due to the management system or to the resistance of adult cattle against nematode infection. Calves are usually raised separately from their dams, and parasites which do not survive the winter on the pasture, have little opportunity to infect calves.
KeywordsNematode Infection Winter Survival Permanent Pasture Sheep Pasture Norwegian Sheep
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