>He's had corrective surgery and our vet managed to stop his resultant >hydronephrosis and his kidney numbers are good. We know that with >cystine stones there sometimes can be a kidney variant where cystine >is not processed properly, but we do not at this point suspect that. Hi Sukie ~ Here's what I know about Cystine. *Two amino acids cysteine and cystine are closely related. Each molecule of cystine consist of two molecules of cysteine joined together. Cysteine is very unstable and is easily converted to L-cystine, but each form is also capable of converting to the other as needed. Both are sulfur-containing amino acids that aid in the formation of skin and are important in detoxification. ** A sulfur containing amino-acid allows cysteine to bond in a special way and maintain the structure of proteins in the body. Cysteine is a component of glutathione. However this is rarely used as a dietary supplement. A more common amino acid used in supplementation is called NAC or N-Acetyl-Cysteine. You should check to see which is included in the food, as NAC is the more commonly favored for most high-protein foods. **Here are the results of trials with NAC: One study found that daily amounts of 1.2 grams or more could lead to oxidative damage. Extremely large amounts of cysteine, the amino acid from which NAC is derived may be toxic to nerve cells in rats. NAC may increase urinary zinc excretion. Therefore supplemental zinc and copper should be added when supplementing with NAC for extended periods. No reference to stones in this text either. *We know that Cysteine works best in the presence of selenium and vitamin E as it helps to detoxify harmful toxins and protects the body from radiation damage. However vitamin B-6 is absolutely necessary for cysteine synthesis, which may not take place as it should in the presence of chronic disease. *The bigger caution is that it inactivates insulin. So if there is any diabetes this supplement should not be taken. There is a rare genetic disorder called cystinuria which leads to the formation of cystine kidney stones. Otherwise I can find no other referencde to kidney stone formation from supplementing with this amino acid, provided all of the complimentary criteria are met. My thoughts go along these lines. When using a more obscure amino acid, or one in which deficiencies have not yet been defined, you get into the dilemma of which other supplements to use to balance the whole thing out. If you don't maintain that delicate balance of vitamins, minerals, and supplements you can get into trouble. Now these findings are for humans, so it's important to know why the makers of these ferret foods put certain ingredients in there in the first place. Ref: (*) "Prescription for Nutritional Healing," by Phyllis Balach, 1997. (There are later editions in bookstores) ISBN# 0-89529-727-2 (**) "The Natural Pharmacy." Lininger, Schuyler,DC (Ed.) 1999 by Healthnotes, Inc., ISBN# 0-7615-1967-X. I hope this gives you a bit of information and can help. Warmly ~ Mary L. Conley, ND, Herbalist Conley Farm Organic Herbs Online Classes www.Herbgrow30.com **************************************** From time immemorial it has been known that Providential Means have placed in nature the prevention and cure of disease, by means of divinely enriched herbs, plants, and trees. ~ Dr. Edward Bach [Posted in FML issue 4569]