Herbal Alternatives to Ivermectin

I remember reading in a book about the history of herbal medicine (I don't recall the title of the paperback book which was purchased in a health food store) that there was a herb used to treat parasites in animals. The drug ivermectin is derived from it. Do you know it? What herbal books would you recommend for reading? I own a veterinary distribution company & would appreciate any help.

Ivermectin is derived from chemicals released by a soil bacterium, Streptomyces avermitilis. It is very toxic and must be used with care.
The are two books covering herbal treatments for animals, both of which are available from Richters. They are: "The Complete Herbal Handbook for Farm and Stable" and "The Complete Herbal Handbook for Cats and Dogs", both by Juliette de Bairacli Levy. The author describes numerous remedies for parasites; an example is this one for worms in sheep: oil of turpentine with linseed oil and garlic, taken for three days.