Which Salmonella enteritidis vaccine, given to laying hens, is specifically protective and helps reduce fecal shedding by protecting ovaries and oviduct?

• A. Live vaccine
• B. Killed vaccine
• C. Subunit vaccine
• D. DNA vaccine

Answer: (B)

The key idea is that protecting the reproductive tract of laying hens can prevent Salmonella from invading the ovaries and oviduct, which in turn reduces egg contamination and fecal shedding. Inactivated (killed) vaccines are designed to induce strong humoral immunity without introducing live bacteria. When given with an appropriate adjuvant, they generate high levels of circulating antibodies that reach the reproductive tract and block Salmonella from colonizing the ovaries and oviduct. This targeted protection helps prevent Salmonella from contaminating eggs and lowers overall shedding.

Live vaccines can boost mucosal immunity but may not provide as reliable protection of internal reproductive tissues and carry more safety concerns in layers. Subunit and DNA vaccines tend to produce more variable protection and may not achieve the same level of protection for the ovaries and oviduct as a killed vaccine, which is why the killed vaccine is considered the best option in this scenario.