Evo was written concerning the issue of cystine stone formation and peas in the diet. Below is their response. Cystine stone formation in ferrets is primarily an inherited disorder in which the pet has an abnormal loss of the amino acid cystine into the urine. Diets high in cystine and/or methionine (a precursor of cystine) from high protein-containing ingredients or from supplemental amino acids can contribute to the amount of cystine lost into the urine, and therefore, increase risk of cystine stone formation. Of the cases reported, many (but not all) of the ferrets who have developed cystine stones have been on pea containing diets designed for the management of food allergies. At this point there is no evidence that peas are directly associated with the development of the cystine stones, and it is thought that the cystine and methionine amino acid content of the diet (including free methionine amino acid supplementation) is likely playing the main role. It should be noted that all of the pea-containing diets that have been associated with cystine stone formation have also been supplemented with methionine. To date, we have received no reports of any ferrets developing cystine stones while being fed EVO Ferret food. -- Debbie, Kindness Matters Ferret Rescue Sponsor a rescue ferret for only $5 per month! [Posted in FML 7662]