2.2. Pigeons

As SPF (specific pathogen free) pigeons are unavailable, sixty six-week-old carrier pigeons were obtained from a private breeder. The flock in the breeding facility is under professional veterinary service and there has been no YPDS history in this flock since 2010. Before the experiment, cloacal swabs and blood samples were collected from all birds to rule out PiCV infection with the use of the qPCR method described previously [35] and to determine the presence of antibodies against PiCV using the in-house ELISA method developed in our previous study [10]. All pigeons were also screened by bacteriological, mycological, and parasitological examinations, and no pathogenic microorganisms were found. The birds were housed in isolated units in a PCL3 biosafety facility of the Department of Poultry Diseases, Faculty of Veterinary Medicine of the University of Warmia and Mazury in Olsztyn. Every group of pigeons was housed in a separate unit. The birds were administered seed mixtures and water ad libitum throughout the experiment.