[The efficacy of anthelmintic drugs against horse strongyles in the area of Salzburg and preliminary results of selective anthelmintic treatment].

In recent years more and more cases of anthelmintic resistant equine strongyles were reported. The latest developments are cases of resistance against macrocyclic lactones. In order to delay this process less anthelmintics and only those which have been previously tested for their efficacy on each individual farm should be used. During the grazing season 2008 faecal samples of 281 horses and 5 donkeys from 26 farms were analysed in the area of Salzburg. To 164 of these horses selective anthelmintic treatment was implemented. Every four weeks faecal samples from the 164 horses were quantitatively analysed for strongyle eggs using a modified McMaster technique. When more than 250 eggs per gram (EpG) of faeces were detected in a sample the horse was treated with an oral pyrantel product. In case of a subsequent faecal sample of the same horse with EpG > 250, Ivermectin, and after the third sample with EpG > 250, Moxidectin was administered. In the fall 2008, all 164 horses together with 117 additional horses and 5 donkeys were treated with Moxidectin plus Praziquantel independent of the faecal egg count. After each anthelmintic treatment a faecal egg count reduction test was performed. In total 1521 faecal samples were analysed. In 1065 samples (70%) no strongyle eggs were detected at all and only 109 samples (7%) had EpG > 250 values. After the treatment with Pyrantel a total of 49 faecal egg count reduction tests, after the treatment with Ivermectin 28 and after the administration of Moxidectin totally 109 faecal egg count reduction tests were performed. After the treatment with either Ivermectin or Moxidectin, all faecal egg count reductions were 100%. On one farm however, the mean reduction of strongyle eggs after the administration of pyrantel was 85.4% on day 14 and 74.9% on day 21. Therefore, faecal egg count reduction tests are strongly recommended whenever horses are treated with Pyrantel.