What happens if a horse receives no vaccines?

The correct answer highlights the significant risk that unvaccinated horses face regarding various diseases. Vaccination plays a crucial role in maintaining a horse's health by protecting against infectious diseases that can be serious, even life-threatening. Without vaccines, horses become more susceptible to illnesses such as West Nile virus, equine influenza, tetanus, and others that could easily be prevented through vaccination.

When horses are not vaccinated, their immune systems lack the necessary exposure to modified pathogens that help build immunity, leading to increased vulnerability to infections. This lack of protection may result in not only severe health issues but also potential long-term consequences for their overall well-being and performance.

The other options do not accurately reflect the role of vaccines in equine health. Immunity cannot be gained without vaccination; performance and growth are unrelated to vaccination status in this context. Vaccination is essential for ensuring not just individual horse health but also the health of the equine population overall, as unvaccinated horses can contribute to the spread of diseases.