Effects of season, age and parasite management practices on gastro – intestinal parasites in pigs kept outdoors in Ireland

Outdoor farming offers pigs considerable behavioural freedom and better consumer acceptance than intensive, indoor systems. However, gastro - intestinal (GI) parasites pose a significant health and welfare challenge for pigs reared outdoors. The aim of this study was to ascertain effects of management, season and animal factors such as age, on a range of different GI parasites in Irish pigs farmed outdoors. Sixty-five pig faecal samples (a mix from at least 2-4 animals per paddock) were collected from 65 paddocks across 20 outdoor pig farms, over two visits (1^st visit - February/May-December 2023, n = 37, 2^nd visit- July/October 2023, n = 28). Samples were collected and mixed thoroughly to achieve a paddock level sample. Data were also collected related to pig characteristics (grower/fatteners or sows and boars), anthelmintic usage (Yes/No) and paddock rotation (Yes/No) and categorized at paddock level. Samples were analysed using the McMaster floatation method, faecal egg count (FEC) was calculated, and GI parasites were identified by morphology. Generalized linear mixed models were used to analyse the effect of season, age, anthelmintic usage and paddock rotation on FEC. Four parasite taxa were identified (Eimeria/Isospora spp., strongyles, Ascaris suum and Trichuris suis). Infection rates were > 80% for Eimeria/Isospora spp. and strongyles, 31% for A. suum and 9% for T. suis for both visits. Eimeria/Isospora spp. FEC was higher at the 2^nd visit (P < 0.001) and strongyles FEC was higher at the 1^st visit (P < 0.05). Fattener pigs had higher FEC for Eimeria/Isospora spp. (P < 0.01) and sows/boars had higher strongyle counts (P < 0.05). Strongyle count was lower with anthelmintic use (P < 0.05) and Eimeria/Isospora spp. count was lower (P = 0.05) with paddock rotation when anthelmintics were used. Lower winter temperatures may have influenced the seasonal variation in strongyle FEC. This study provides a comprehensive picture of GI parasites in outdoor pig farms in Ireland in terms of the taxa, their prevalence and risk factors.