Gastrointestinal parasites in Swedish pigs: Prevalence and associated risk factors for infection in herds where animal welfare standards are improved

The global pig production has undergone major changes over the past 30 years with larger farms, more intensified production as well as improved hygiene and biosecurity practices. To investigate whether these changes, along with expanded pig welfare, have had an impact on parasite occurrence, a cross-sectional study was conducted in Sweden on farms where the pigs are always loose-housed, floors are solid and bedding material is provided. A total of 1615 faecal samples were collected on 42 conventional indoor farms from a) post-weaning piglets (n = 337); b) growers (n = 345); c) fatteners (n = 308); d) dry sows (n = 277) and e) pre-partum sows (n = 348). Samples were analysed using centrifugal flotation with a saturated glucose-salt solution and a modified McMaster technique, with a lower detection limit of 50 eggs or oocysts per gram. Samples positive for strongyle-type eggs were cultured to third stage larvae for genus identification. Farms also responded to a questionnaire regarding biosecurity, hygienic measures, and other management routines. Risk factors for parasite occurrence were assessed using mixed-effects logistical regression to account for farm-level clustering of samples. Interestingly, the prevalence of Ascaris suum was reduced compared to a similar investigation in the 1980s. In the present study A. suum was detected only in 43 % of the herds, with the highest prevalence in pre-partum sows (37 %) followed by fatteners (25 %). Small sized farms were associated with higher odds of being positive, compared to large sized farms (OR = 159.1, P = 0.010). Oesophagostomum spp. were detected in 64 % of the herds and again mainly in pre-partum sows (63 %). Trichuris suis was detected in 10 % of the herds but only in <1% of the samples. Moreover, Cystoisospora suis and Eimeria spp. were detected on 60 % and 64 % the farms, with the highest prevalence in post-weaning piglets and sows, respectively. Anthelmintic drugs (ivermectin or fenbendazole) were commonly used and administered mainly to pre-partum sows on 93 % of the farms. Toltrazuril against neonatal coccidiosis was administered to piglets on 14 % of the farms. The use of antiparasitic drugs did not significantly affect parasite prevalence. Overall, it appears that the altered farming routines with focus on improved pig welfare have not solely resulted in a higher occurrence of parasites, most likely due to the adequate biosecurity and hygiene practices instituted. Thus, there seems to be no conflict between implementing measures to promote pig welfare and adequately control the more pathogenic and economically important parasites.