Why are sheep particularly susceptible to internal worms?

Sheep are particularly susceptible to internal worms because they graze low to the ground. This grazing behavior allows them to consume not only grass but also potentially contaminated forage where larvae of parasites such as nematodes and cestodes are present. These parasites thrive in the environment close to the ground, and by grazing in this manner, sheep increase their likelihood of ingesting these infectious stages of worms. Additionally, the close-to-ground grazing can lead to higher exposure to contaminated feces, where worm eggs are shed, contributing to the risk of internal worm infestations.

In contrast, grazing high up or consuming only dry food wouldn't expose the sheep to the same level of risk from internal parasites because these options do not coincide with the habitats of many common worm larvae. Consuming too much water does not directly relate to worm susceptibility either and doesn't reflect the grazing behavior that influences exposure to these internal parasites.