Long-term survey of Eimeria spp. prevalence and faecal shedding in a traditional Portuguese free-range broiler farm

In free-range broiler production, animals are highly exposed to gastrointestinal parasitism, namely by coccidia, due to their long contact with the outdoor environment. Also, the prevalence of gastrointestinal parasites in extensive poultry production, is frequently influenced by biotic and abiotic factors. The current national pioneer long-term survey aimed to assess the prevalence and faecal shedding of Eimeria spp. oocysts in a traditional Portuguese free-range broiler farm, on different production conditions. Between July 2018 and March 2019, a total of 350 faecal samples were collected from different groups of free-range broilers at the fattening phase, in a poultry farm located in North-western Lisbon district, Portugal. Quantitative and qualitative coprological techniques were performed, aiming to quantify the Eimeria spp. prevalence and faecal shedding level. Coccidia prevalence was higher in Summer and Autumn groups (72% and 80%, respectively), although faecal shedding levels were higher in the Autumn and Winter groups (1191 and 1562 Oocysts Per Gram, OPG). Animals showed clinical signs of coccidiosis during the survey, especially in Autumn’s 1st sampling, in which 42% of the faecal samples had blood. The lack of sanitary depopulations, length of the fattening phase (1 month), short pre-patent period of coccidia, exposure to different environmental conditions and irregular drug treatments with amprolium, were key factors responsible for the different parasitic scenarios observed during this survey.