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

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.

Keywords: Strongylus vulgaris; deworming; faecal sample; parasite control.

Figure 1

Equestrian premises where Strongylus vulgaris was found to be present (at least one positive horse), expressed in percentage per year.

Figure 2

Proportion and number of Strongylus vulgaris-positive equestrian premises where larval cultures had been performed on either individual (blue) or pooled samples (orange).

Figure 3

Occurrence of Strongylus vulgaris in 2013–2016 in relation to egg-shedding level expressed as EPG (eggs per gram) range. Number of horses are shown above the bars.

Figure 4

Proportion (y-axis) and number (indicated in the bars) of horses in different EPG (eggs per gram) levels per age category between 2009, the first year when age was recorded, and 2016, the last year when McMaster egg counting was performed.

Figure 5

Individual EPG (eggs per gram) for horses that were analysed in 2008–2016. The majority of eggs were shed by a few horses.

Figure 6

Yearly occurrence of Anoplocephala perfoliata eggs in faecal samples. In 2017, samples were analysed by a modified flotation method based on 30 g of faeces, while McMaster on 3 g of faeces was used in previous years.