[Repeated dehelminthization and its effect on the course of the natural infestation, of sheep by roundworms].

Long-continued use of levamizole for the control of gastrointestinal roundworms in sheep kept on pasture showed that the discrepancy in the results obtained in experiments and in the terrain is associated with the physiology of host and parasites. In practical use in the terrain, the preparation had an 85% effect in one case; otherwise the average effect was 61.1% and persisted five to six weeks in all flocks including those in which the animals were treated five times a year.

[Pastures as a source of helminthiasis invasions in sheep and cattle].

The aim of the study was to find out the influence of naturally invaded environment on heifers and sheep grazing in the open air for the first time, and/or possibilities of parasite transmission between domesticated and wild ruminants. Larvae were proved to be able to survive 11 months in the environment, even if the eggs had been eliminated with excrements to the grass in July at a high temperature of 26 degrees C. For instance, the larvae Nematodirus, Ostertagia, Chabertia and Trichostrongylus, belonging to the most resistant, survived from the July of one year to the June of the subsequent year in a closed sheep-run located on the pasture and excluding a possibility of access of other animals.

[The effect of dehelminthizations performed during the year on the seasonal dynamics of natural nematode infections in sheep].

In four sheep flocks of two age categories dynamics of natural infections by pulmonary and gastrointestinal nematodes was studied; sheep were kept on a farm in Western Bohemia. Dehelminthizations were performed in different intervals during the grazing period on the basis of the results of quantitative coprologic examinations. Total effectiveness of 80--100% intenseffectiveness (IE) was obtained as a result of single peroral or intraruminal dehelminthization with the following preparations: pyrantel hydrochloricum (Spofa), helmatac (SKF) and nilverm (ICI); the effectiveness concerned gastrointestinal nematodes of the genus Haemonchus, Cooperia, Ostertagia, Trichostrongylus, Bunostomum, Chabertia, Nematodirus, Strongyloides, Oesophagostomum and Trichocephalus.