Which method is not effective in ensuring an animal's immunity?

The choice indicating that ignoring routine checkups is not effective in ensuring an animal's immunity is correct because routine checkups are critical in monitoring the overall health of an animal, including its immune system. During these checkups, veterinarians can assess the animal’s vaccination status, evaluate any potential health issues, and provide timely vaccinations or boosters where necessary.

Regular vaccinations are essential for building and maintaining immunity against specific diseases. Retesting antibody levels after immunizations can also provide valuable information about an animal's immune status and whether further vaccinations are needed to ensure adequate protection. Preventing exposure to infectious diseases is crucial for health, but without regular checkups, there might be gaps in vaccination schedules or unchecked health issues that could compromise an animal's immunity. Therefore, ignoring routine checkups directly undermines the effectiveness of other methods aimed at ensuring an animal's immunity.