What is the main purpose of giving vaccinations to farm animals?

The correct option is: To protect them from major viral and bacterial diseases.

Vaccination is a preventive veterinary practice where a biological preparation (a vaccine) is administered to farm animals. This preparation typically contains weakened, killed, or parts of disease-causing microorganisms (pathogens) such as viruses or bacteria.

When administered, the vaccine stimulates the animal's immune system to produce antibodies and develop immunity against these specific pathogens. If the animal is exposed to the actual disease-causing viral or bacterial pathogens in the future, its immune system can quickly recognize and fight off the infection, thereby protecting the animal from contracting major diseases.

Let us look at why the other options are incorrect:
• Preventing attacks from external parasites: Parasites like ticks, lice, and mites are controlled using parasiticides, dips, or sprays, not vaccines.
• Increasing milk production: While healthy animals produce milk optimally, vaccines do not directly increase milk production; that is managed through nutrition, breeding, and general husbandry.
• Improving the quality of animal feed: Feed quality is determined by crop formulation, ingredients, and processing, which is entirely independent of animal vaccination.