In horses how long does it take to kill worms after a dewormer?

Depends on the wormer. The products that are systemic last much longer.

Feed through products and those that only kill parasites in the intestinal tract have a much shorter activity period.

Products like moxydectin deposit in the animal's adipose tissue and continue to be released over time. This is the reason this anhelmenthic is not recommended for

foals or animals that are underweight.