All livestock have parasites, some of which cause problems such as ill health and low productivity.
Nematode worms that live in the digestive tract of goats and sheep are of great concern to farmers. These worms are found all around the world and there are many methods for controlling them. The main method has been to give chemicals by drench or injection. But now these chemicals are becoming less useful as the worms become resistant to their effects. And in the tropics chemicals are often too expensive, not available, or of uncertain quality.