For 9 consecutive months (March-November 2008), faecal samples were collected monthly from 129 horses residing within 40 km of Salzburg, Austria. Samples were analysed quantitatively using a modified McMaster egg counting technique. Whenever a faecal egg count (FEC) result exceeded 250 eggs per gram (EPG), the horse was treated with pyrantel, ivermectin or moxidectin. In 52 of 129 horses (40.3%), no strongyle eggs were ever detected over the course of 9 months. In 39 horses (30.2%), strongyle eggs were detected in at least 1 sample, but the egg count never exceeded 250 EPG. The remaining 38 (29.5%) horses were treated at least once in response to a FEC that exceeded 250 EPG. As a result of this selective anthelmintic scheme, the total number of anthelmintic treatments was reduced to 54% of the number of treatments administered to the same horses in the previous year. Both the maximum and mean FEC dropped significantly after initiation of the study. A statistically significant, negative correlation was demonstrated between the maximum and mean FEC of a horse and its age. Pasture hygiene appeared to reduce FECs, but the effect was not statistically significant. The magnitude of the initial FEC was significantly correlated with the maximum FECs in the subsequent 8 months (p<0.01). The same relationship was observed for the maximum FEC of the first 2 samples. Furthermore, horses which required several anthelmintic treatments had a higher initial FEC and a greater maximum FEC in the first 2 samples than horses which received only one or no treatment. These results suggest that selective anthelmintic treatment accomplished a reduced pasture contamination with strongyle eggs, while simultaneously decreasing the number of anthelmintic treatments. Sustained implementation of a selective treatment strategy has the potential to reduce selection pressure for anthelmintic resistance. These results reported herein will assist equine practitioners in designing and monitoring sustainable anthelmintic treatment programs.

BackgroundAs a consequence of the increasing levels of anthelmintic resistance in cyathostomes, new strategies for equine parasite control are being implemented. To assess the potential risks of these, the occurrence of strongyles was evaluated in a group of 1887 horses. The distribution of fecal egg counts (FECs), the frequency of anthelmintic drug use, and the deworming intervals were also analyzed. Between June 2012 and May 2013, 1887 fecal samples from either selectively or strategically dewormed horses were collected at 195 horse farms all over Germany and analyzed quantitatively with a modified McMaster technique. All samples with FEC ≥20 eggs per gram (EPG) were subjected to coproculture to generate third-stage larvae (LIII) for species differentiation.ResultsEgg counts were below the limit of detection (20 EPG) in 1046 (55.4%) samples and above it in 841 (44.6%) samples. Strongylus vulgaris larvae were identified in two of the 841 positive samples. Infections with cyathostomes were found on every farm. The most frequently applied anthelmintic was ivermectin (788/50.8%), followed by pyrantel (336/21.6%). The mean time since last treatment was 6.3 months. High-egg-shedding (>500 EPG) strategically dewormed horses (183/1357) were treated, on average, three times/year. The planned treatment date was already exceeded by 72.5% of the high egg-shedders and by 58.1% of the moderate (200–500 EPG) and low egg-shedders (20–199 EPG).ConclusionsS. vulgaris seems to be rare in Germany and no difference in its frequency has yet been found between selectively treated horses and horses receiving treatment in strategic intervals. However, inconsistent parasite control has been observed. Therefore, to minimize the risks for disease, consistent and efficient parasite control should be implemented.

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