Dan, do you know what kind of bladder stones these are? Knowing what they are is extremely important in deciding whether or not Zupreem grain free food might be responsible. When your second ferret has surgery, you need to have your vet send one of the stones to a lab for examination if this was not done when your first ferret developed stones. Ferrets can get several types of stones, and each type will have a different cause. The most common type of stone found in ferrets is the struvite stones. Struvite stones have not been linked to pea protein (the ingredient in Zupreem grain free being blamed for bladder stones). Struvites are composed of three things: magnesium, ammonium and phosphate; therefore, avoid excessive amounts of these three things in the ferret's diet. Magnesium is the most important one to limit. Struvite stones form because the pH of the urine becomes too high. Kibble containing grains can raise the pH of the urine, because plant based protein does not contain the 2 amino acids that contain sulfur. When these two sulfur-containing amino acids are metabolized, they produce sulfuric acid. When sulfuric acid is excreted into the urine, it lowers the pH of the urine and prevents Therefore, a diet of kibble containing grains may lead to the formation of bladder stones. Calcium oxalate stones are the second most common type of stone found in ferrets. They occur when the ferret's diet contains too much calcium and oxalate, and when the pH of the urine is too high. Oxalate is formed when the body metabolizes plant protein. So, again, having a lot of plant protein in the food can lead to the formation of this type of stone. The third type of stone found in ferrets is cysteine stones. Cysteine stones are actually somewhat rare, and are caused by a genetic defect in the kidneys. The defect causes kidneys to be unable to reabsorb the amino acid cysteine. Cysteine solubility depends on urine pH, and cysteine stones are more likely to form in acidic urine. Cysteine stones are the stones that some people think may be caused when a ferret has the specific genetic defect in the kidneys and eats a diet that contains pea protein. However, there have been no studies done to confirm this hypothesis. So, contacting Zupreem at this time might be pointless, as until there is proof that pea protein plays a role in the formation of stones, Zupreem would likely not take a complaint seriously. So, before you blame Zupreme for your ferrets developing stones, you definitely need to find out what kind of stones you are dealing with. If they are struvite or calcium oxalate stones, it is very unlikely that Zupreem had anything to do with the problem. If they are cysteine stones, then you need to push for a study to learn whether or not pea protein really has an effect on the solubility of cysteine. Danee DeVore ADV - If your ferret hasn't been tested, you don't know! See - http://www.ferretadv.com/ Owner of The Clay Ferret Quality Kits Raised With Love Color Logo TCF [Posted in FML 8148]