What substance is administered to an animal to create immunity to diseases?

The correct choice is a vaccine, which is a biological preparation that provides active acquired immunity to a particular infectious disease. Vaccines typically contain an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. When introduced into the body, the vaccine stimulates the immune system to recognize the agent as a threat, destroy it, and "remember" it, so that the immune system can recognize and respond more effectively to future encounters with the pathogen.

Antibiotics, while crucial for treating bacterial infections, do not create immunity; they work by killing bacteria or inhibiting their growth. Sedatives are used to calm or sedate an animal but have no role in preventing diseases. Hormones are chemical substances that regulate various physiological processes within the body, such as growth and metabolism, and are not related to disease prevention.