In the life cycle of internal parasites in ruminants, how do animals commonly become infected?

• A. Ingesting adult worms
• B. Absorbing L3 larvae from grass
• C. Drinking water only
• D. Through skin contact

Answer: (B)

Grazing animals typically become infected by swallowing the infective third-stage larvae (L3) that are on pasture. The life cycle starts with eggs shed in feces, which hatch and develop to L3 in the environment. These L3 larvae cling to grass blades, and when the animal bites and ingests forage, the larvae are swallowed and migrate to the digestive tract where they mature into adult worms. This route—ingestion of L3 on grass—is why it’s the best answer. Ingesting adult worms isn’t how infection occurs since adults live in the gut, not on pasture. Drinking water or skin contact aren’t the main routes for these gastrointestinal nematodes.