Reduced efficacy of anthelmintics in cattle nematodes.Original Title Verminderte Wirkung von Anthelminthika gegen Rindernematoden.

摘要

The productivity of young grazing cattle is mainly affected by infections with gastro-intestinal nematodes. Worldwide anthelmintic resistance (AR) is increasingly jeopardizing effective worm control in many regions. Detection of existing AR is the first step to postpone the spread of resistant genotypes. Results of a field study, performed in the years 2006 and 2007, revealed a reduced efficacy of avermectine against gastro-intestinal nematodes used for deworming first-season-grazing calves on German dairy farms. On nearly half of farms analysed, reduction of faecal egg output on day 14 post ivermectin treatment failed to meet the international criteria for complete efficacy. In contrast treatment with the benzimidazole albendazol showed full efficacy on ten additional farms. The evaluation of two in vitro tests for the detection of anthelmintic resistance (Larval Migration Inhibition Test, Egg Hatch Test) indicated that improvement regarding cost effectiveness and establishment of reference values are required. A minimized use of anthelmintics could help to delay the development of AR. To define criteria used for targeted, selective treatment of individual grazing calves, several data points concerning body condition and faecal egg count were compared. No significant correlation was found between the two parameters, possibly due to low nematode infection rates, while the correlation between body weight and the heart girth tape value was high (r=0.982).