Kurt has a lot of great practices to help reduce parasites!
When it comes to parasites, there is no magic bullet -- not even a modern drug! A vet professor told me about ten years ago that no one would ever get total control of worms by using dewormers. It has to be a multi-pronged approach. She also said it's impractical to think that you will ever have goats with zero worms. Since then I've learned that zero worms would not even be desirable. Parasites in the goat would not exist if it were not for goats. If the goat dies, the parasite dies because it can only live in the goat, so these two species have traveled through time together to co-exist. The parasites are probably doing something positive, even though we have no idea what. From a biodynamic perspective, some speculate that they act as aerators in the rumen just as earthworms aerate the soil. Hmm ... food for thought! So, our goal should not be to eradicate the worms, which is basically the mindset of the pharmaceutical companies. Worms only become a problem when the load gets to be too high, which generally happens with overgrazing, or when an animal is already being stressed by something else, such as birth or moving to a new farm.
Various things that research has proven to be effective -- rotational grazing, multi-species grazing, copper oxide wire particles, tannin plants, and papaya seeds.
Pasture rotation is really important to keeping your goats from having a problem with parasites. We had zero problems the first two years we had goats because we didn't have very many goats. I used absolutely nothing for those first two years and thought everyone was just wasting their money on dewormers. Then I had a goat die, and the necropsy showed parasites as the cause. The problem was that we had too many goats on the pasture, and they were re-ingesting too much larvae, so the burden in their guts became too big.
As they say, an ounce of prevention is worth a pound of cure, and that is definitely true with goats. Once you get your nutrition and management figured out, you will have very few problems.
Here is an excerpt from Raising Goats Naturally on preventing parasite problems, including all the things I just mentioned except papaya seeds and copper oxide wire particles:
http://www.homegrownandhandmadethebook.com/2015/04/internal-parasite-in-goats-preventing.html
Unfortunately the week after the book went to press, a study was released on using papaya seeds as a dewormer. I was super excited about that, so next time one of my goats had a parasite overload, I ran out and bought a papaya! The dosage used in the study was 10 grams per day for 10 days. I quickly learned that a papaya only had about 30 grams of seeds in it, and three days of seeds didn't do anything to reduce my goat's parasite level, and unfortunately I live an hour away from a store that sells papaya seeds. But if you live in an area where papayas are readily available, you might want to give this a try. Here is an article that gives a few more details:
http://news.ifas.ufl.edu/2013/06/ufifas-expert-promising-results-from-papaya-for-parasite-plagued-goats/
There have been more than a dozen studies done showing the effectiveness of copper oxide wire particles (COWP) in reducing parasite loads in goats. Also, a goat that is copper deficient will have a much harder time dealing with a "normal" load of parasites, so the copper serves two important functions when it comes to parasite control. A lot of the studies were also done on sheep, and they never had a case of toxicity in the sheep, so as long as you don't overdose, you shouldn't have to worry about toxicity in goats (who can handle at least 4 times as much copper as sheep) when using COWP. A word of warning about copper -- there is a popular herbal book out there that recommends using copper sulfate for worms. Copper sulfate is much better absorbed into the system than copper oxide, and the only copper toxicity case study I could find in the literature was in a herd that was using a cattle mineral with 3000 ppm copper sulfate in it. Also, I've met several people online who've had goats die when they gave them copper sulfate for worms, so it's better to stick with the copper oxide, which is what has been used in the studies. They dosed at 1 gram per 20 pounds.