Evaluation of mucin expression, intraepithelial lymphocytes and cytokines in the caecum of broilers protected with Enterococcus faecium EF55 and challenged with Salmonella enteritidis SE147 / Martin Levkut, Viera Revajová, Viera Spišáková, Róbert Herich, Zuzana Ševčíková, Mária Levkutová, Mikuláš Levkut KE304