This is an experiment for me, I'm not recommending it to any one else. It seems that there is a broad spectrum of plants that have anti-nematodal / anthelmintic activities. The trick is in getting the correct amounts and most effective combination. I will do some fecals and start tracking it's effectiveness and see what happens. I'm hopeful. It is less expensive than using the chemical dewormers (and I'm going to try to grow all my own ingredients!) and theoretically not as hard on an animal's system.

I will give general recommendations about deworming no matter whatever you are using. I highly recommend getting fecal counts done (taking samples to your vet would be the easiest way!). Then you know exactly what you need to worm for!
Diatomaceous Earth has become a great friend and gets put everywhere any animals sleep (chicken coop, rabbit hutches, stalls) and high use areas such as entry ways. I only use it externally. I know that lots of people include it in their wormers for internal use but it doesn't make sense to me to use it that way. It works by cutting the exoskeleton of insects and they dry out. Internal parasites don't have chitinous exoskeletons as a general rule.
For the herbal preparation I have used equal parts of
fennel seeds,
dehydrated garlic,
oregano,
thyme,
sage,
hyssop,
red clover and
pumpkin seeds. I also add in
Wormwood, although not on any pregnant animals. I added some
mint as well as a thought at the time.
It is suggested to deworm in spring and summer by adding to feed rations (I put it in the beet pulp for horses and goats and in grain for the chickens) for the first week of every month:
Horses: 1/4 cup daily
Goats: 1 TBSP daily
Chickens: about 1 cup per 30 chickens daily
Wormwood
Various forms of {Artemisia absinthium} have been shown to reduce internal parasite loads in experiments with a variety of animals. The plant's odor can also be useful in spraying against pests.
Pumpkin seeds
Pumpkin seeds are a good source of amino acids (including tryptophan), vitamins, and minerals (such as iron, magnesium, manganese, phosphorus, zinc) and phytosterols. The seeds have been shown in research to have anti-nematode properties and are noted by some for expelling tapeworms from the body.
Hyssop
{Hyssopus oficinalis} is a common perennial herb. The entire plant is traditionally used medicinally but most typically the flowering tops and leaves. Hyssop’s therapeutic actions are believed to be due to its essential oil, which is thought to have anthelmintic properties but I haven't found any research to corroborate that.
Garlic
{Allium Sativum} has been used as an anthelmintic for centuries and is believed to have antibacterial, antimycotic and lipid-lowering effects. One paper concluded that it doesn't affect gastrointestinal nematodes in goats or sheep (1). However in another paper they showed that garlic was effective against an intestinal parasite in people, showing a great reduction in both the egg and worm burden (2).
Garlic is thought by many to be toxic to horses, however research looking into it found problems starting with a daily dose of > 0.2 g/kg. That would be 80 grams for a 400kg horse and one clove of garlic weighs around 6 grams. Also, once they fed over a cup a day of garlic the horses started refusing their feed with the garlic in it prior to reaching problematic levels. (3)
Fennel seed
Although many tout the anthelmintic properties of {Foeniculum vulgare} I couldn't find any research on it. It is traditionally used to sooth sore stomachs by decreasing the formation of gas in the intestinal tract.
Sage
{Lamiaceae} is part of the mint family. It has also traditionally been labeled an anthelmintic, however I can't find any research on it.
Oregano
{Origanum vulgare} is a genus of the mint family. It has been shown to have antimicrobial properties. Perhaps the best use of this herb is to use an oil extract externally.
Red Clover
{Trifolium pratense} is a very rich source of isoflavins, but I haven't found any more information towards decreasing any parasitic infection.
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Conclusions:
Unfortunately there isn't a lot of research on using herbs yet and many go by traditional beliefs, often that show some merit. There is one article I found investigating the efficacy of herbal dewormers on goats (4). It found no effect of the herbal dewormer to control gastrointestinal nematodes. However I don't have access to that article and I don't know which herbs they used, what doses, etc. I will add my conclusions as I do fecals and find out how my animals react to the herbal worming protocol. I will also do adjustments as I go! More to come.
One thing that I found to be cool is that even if I found pumpkin seeds not to have any effect, I would still feed them to the horses. We had a great pumpkin patch growing on one side of the manure pile!!
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1. Burke, Wells, Casey, Miller.
Garlic and papaya lack control over gastrointestinal nematodes in goats and lambs. JE.Vet Parasitol 2009 Feb 5;159(2):171-4. Epub 2008 Oct 15.
2. Nahed, Hoda, Yomna.
Effects of garlic on albino mice experimentally infected with Schistosoma mansoni: A parasitological and ultrastructural study. Trop Biomed. 2009 Apr;26(1):40-50.
3. Pearson, Boermans, Bettger, McBride, Lindinger.
Association of maximum voluntary dietary intake of freeze-dried garlic with Heinz body anemia in horses. Am J Vet Res. 2005 Mar;66(3):457-65.
4. Burke, Wells, Casey, Kaplan.
Herbal dewormer fails to control gastrointestinal nematodes in goats. Vet Parasitol 160(1-2):168-70. Epub 2008 Nov 1.
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(Note: Wormwood, Annis and fennel are the main herbs used in the preparation of absinthe, an alcoholic mixture which originated as a medicinal elixir in Switzerland and became, by the late 19th century, a popular alcoholic drink in France and other countries.)