Prebiotics are non-digestible dietary carbohydrates (e.g., fructooligosaccharides, mannan-oligosaccharides, inulin) that selectively stimulate beneficial gut microflora.

• Mechanism of Competitive Inhibition: Oligosaccharide prebiotics like MOS act as receptor analogues (decoys); enteric pathogens like Salmonella and E. coli bind to MOS via their type-1 fimbriae instead of intestinal mucosal cells, directly preventing pathogen colonization.
• In the official NTA Final Answer Key, both Option 2 and Option 3 were accepted as correct answers.

Newcastle disease (Ranikhet disease) is primarily transmitted horizontally via inhalation of infectious aerosols or ingestion of contaminated feed/water. In contrast, Salmonella Pullorum, Avian encephalomyelitis, and Mycoplasma gallisepticum are well-known vertically transmitted egg-borne avian pathogens.

Marek's disease vaccine (cell-associated herpesvirus of turkeys - HVT or bivalent Marek's vaccine) requires primary cell cultures (chicken embryo fibroblasts) prepared from certified Specific Pathogen Free (SPF) eggs.