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Gastrointestinal Nematodes are widespread nematodes of cattle in the temperate climate zone and worldwide. The most common species are Cooperia oncophora and Ostertagia ostertagi, which live in the abomasum and small intestine of generally all grazing cattle. The increase of anthelmintic resistance becomes more important in the cattle farming and milk production branch. In Europe, New Zealand and South America decreased efficacy of different anthelmintics has already been recorded. Therefore, systemic treatment of whole flocks is no longer justifiable and there is the need to develop other parasitic management strategies. The aim of this study was to evaluate thresholds for already developed parameters, which can be used for treatment decision in targeted selective treatment- and targeted treatment-strategies.
The decision criterions for a selective usage of anthelmintics for heavily infected animals were either a combination of a high fecal egg count (≥ 250) and a low daily weight gain (≤ 250 gram/day) or a high fecal egg count (≥ 250) combined with a decreasing Body Condition Score. During the grazing-season in 2010 two groups of first-grazing cattle were treated in two different ways: One group served as control group and was regularly treated with Ivermectin (Ivomec®). The other group did not receive a systemic treatment; if required, the animals were treated according to targeted selective treatment-strategies. The calves were weighed, the Body Condition Score was measured and individual sampled (blood and faeces) in intervals of 14 days between May and November.
The faecal samples were analysed using sedimentation, a Baerman-funnel system and the modified McMaster method to determine individual fecal egg count. The blood samples were examined using different Serum-Enzyme Linked Immunosorbent Assay to detect antibodies against Fasciola hepatica and Dictyocaulus viviparus. During the grazing-season in 2011 this approach was repeated in a modified set-up. Two group were treated according to targeted selective treatment-strategies and targeted treatment-strategies, respectively.
A control group was regularly treated with anthelmintics. The sampling was repeated at intervals of 14 days during the grazing-season from May till November. The statistical analysis resulted in no significant difference in the total weight gain of the groups, although the usage of anthelmintics could be significantly reduced. Furthermore, clinical signs could not be detected at any time during the study. The fecal egg count of the first season grazing calves was low in both years. By reducing the usage of anthelmintics the treatment costs of the animals were kept markedly low. In both years there was a good correlation between the bodyweight and the Body Condition Score; this procedure seems to be suitable to evaluate the body condition of first season grazing cattle. In both years a decreased efficacy of macrocyclic lactones was noticed. The presence of anthelmintic resistance considering macrocyclic lactones was confirmed by the results obtained from a Faecal Egg Count Reduction Test and Larval Migration Inhibition Assay. The Faecal Egg Count Reduction Test performed with anthelmintics belonging to the benzimidazole-group revealed no hints of anthelmintic resistance against this chemical group; there was no evidence for reduced efficacy of benzimidazole. Deoxyribonucleic acid isolation was performed using the larvae obtained from the Larval Migration Inhibition Assays (migrated and non-migrated).
Both fractions were subsequently used to perform a qualitative polymerase chain reaction in order to detect the presence of Cooperia oncophora and Ostertagia ostertagi.
It could be shown, that only Cooperia oncophora was able to migrate in the presence of high concentrations of Ivermectin. In total, the results of the present study show that it is possible to use targeted selective treatment- and targeted treatment-strategies also for young grazing cattle. Thresholds of decision parameters for the selection of treatment were successfully established and evaluated under field conditions, which led to a significant decrease in use of anthelmintics without problems regarding animal health and productivity. Particularly for the ecological farming system a great potential can be seen in these strategies as preventative and strategic anthelmintic use is greatly restricted here. Because the targeted selective treatment- and targeted treatment-strategies, using the parameter mentioned above, do not detect involvement of Fasciola hepatica and Dictyocaulus viviparus, there should be additional tests in predisposed areas.
At least the described results need to be validated in further studies with more animals.