FFA Vet Science CDE Practice Exam 2025 – All-in-One Guide to Succeed in Future Farmers of America Competitions!

In vivo vaccination refers to the process of administering a vaccine directly into a living organism, where the immune system can respond to it. The most effective method for certain types of vaccines, especially in avian species like chickens, is through the injection into the embryo within the egg. This approach allows for the development of immunity before the chick hatches, providing early protection against diseases.

Administering the vaccine to the embryo in the egg ensures that the immune system is primed while the chick is still developing, leading to stronger immune responses and better overall health once the bird hatches. This method capitalizes on the natural development processes of the embryo, enhancing the efficacy of the vaccination.

The other mentioned options are less ideal for in vivo vaccination in this context. For instance, while a newborn chick can receive vaccines, doing so post-hatch may not provide the same immediate immunity as vaccinating in ovo (inside the egg). Likewise, a hen's uterus and a pullet (a young hen) are not standard sites for vaccination in terms of ensuring the most effective immune response as seen in embryo vaccination.