Selective Anthelmintic Treatment in Horses in Sweden Based on Coprological Analyses: Ten-Year Results

SIMPLE SUMMARY: In the past, horses were protected from parasitic infections by routine deworming aimed at keeping harmful worms such as Strongylus vulgaris under control. The emergence of drug-resistant worm populations has stimulated the introduction of alternative control strategies to reduce the frequency of antiparasitic treatments. In Sweden, selective treatment is recommended, and deworming should be based on the results of faecal analyses, where individual horses that contribute substantially to pasture contamination are treated. In our study, horses from equestrian premises across Sweden participated in a parasite monitoring programme during the years 2008–2017. Faecal samples were collected in the spring and in the autumn in order to identify which individuals should be dewormed. According to the results obtained from the spring analyses (March to June), the use of antiparasitic drugs could be greatly reduced when selective treatment is chosen instead of routine treatment. ABSTRACT: In Sweden, routine deworming has been used for several decades; however, to slow down the development of anthelmintic resistance, selective treatment is currently recommended. As part of a monitoring programme, equestrian premises submitted faecal samples to the National Veterinary Institute (SVA) twice per year between 2008 and 2017. Analyses for strongyles (small and large), tapeworms and ascarids, followed by premise-specific advice regarding deworming and parasite control strategies, were provided. In total, 43,330 faecal samples, collected from 26,625 horses on 935 premises in springtime (March to June), were analysed by quantitative or semi-quantitative flotation. Moreover, Strongylus vulgaris was detected by larval culture or PCR. Between 4 and 11% of individual horses tested positive for S. vulgaris and 3–10% were shedding tapeworm eggs. There were recurrent high and low egg shedders; 75% of horses with S. vulgaris appeared to have been recently introduced into the herd; the proportion of S. vulgaris-positive premises increased when individual samples rather than pooled samples were used. Based on the results of S. vulgaris diagnostics and strongyle egg-shedding level, 59% of the horses did not need to be dewormed.