Concept:A parasite lives on or inside livestock and obtains food and shelter from the host, causing harm and lowering productivity.
Explanation:A parasite directly depends on livestock for nourishment.
This weakens the animal and reduces its yield of milk, meat, or eggs.
A predator kills the animal instead of deriving benefit while keeping it alive.
A pathogen causes disease, but it is not mainly described as benefiting from the host.
A microbe is a broad term and not every microbe reduces productivity by living on livestock.
Therefore, the biotic factor that derives much benefit from livestock and reduces productivity is a parasite.
Answer:B. parasite