Gastroenteritis, caused by Salmonella spp. and pathogenic Escherichia coli, often appears in early stages of poultry and swine production and has become a major problem in animal nutrition since the ban on antibiotic feed additives in 2006. Phytogenic feed additives (PA) represent a non-antibiotic alternative. The present studies prove that the tested PA from broccoli (BE), turmeric (GÖ), oregano (OÖ), thyme (TÖ), and rosemary (RÖ) do not improve performance parameters of farm animals, but seem to be beneficial in early feeding stages of broiler and piglets. OÖ primarily possessed direct antioxidant effects, while BE and RÖ rather developed their antioxidant properties in vivo by induction of xenobiotic and antioxidant enzymes. Direct and indirect antioxidant effects via Nrf2 were also demonstrated for the TÖ and GÖ. There could not be detected any anti-microbiotic properties of PA in vivo. Additionally, the present work indicates anti-inflammatory effects of PA due to the reduction of NFB and Cox2 mRNA concentration under physiological and stimulated conditions (DSS-colitis in rats, Escherichia coli-infection in IPEC-J2 cells).