UC Davis Vet School Raw Diet Study (2002)

Apparently the only study of raw diets in cats that has any pretense of being "scientifically valid," was one done in 2002 at the Center for Companion Animal Health, School of Veterinary Medicine, University of California, Davis, entitled Role of Diet in the Health of the Feline Intestinal Tract and in Inflammatory Bowel Disease. The report of the study can be found here.

From the report:

After one week in the study, the cats on the rabbit diet all had significant improvements in their stool quality based on a visual stool grading system (developed by the Nestle-Purina PetCare Company). After one month, the cats on the rabbit diet all had formed hard stools, while the commercial diet cats had soft formed to liquid stools. These differences persisted to the end of the feeding trial. The cats that were fed the whole rabbit diet outwardly appeared to have better quality coats, but objective measurements were not made. Interestingly, we could find no relationship between the type of diet consumed and: 1) the rate of growth, 2) degree of inflammation in the tissue lining the intestinal tract, or 3) the numbers of bacteria in the upper small intestine. The numbers of cats shedding pathogenic type organisms (Giardia and Cryptosporidia species) were on average slightly higher for the cats that were fed the raw diet. Therefore, it appeared that the raw rabbit diet did not have its beneficial effects on stool quality by reducing pathogenic organisms in the intestine, altering the numbers of bacteria in the small intestine or by diminishing the levels of inflammatory changes in the intestinal wall.
Although it appeared that the raw rabbit diet was significantly beneficial for the stool quality and appearance of health in the cats, the sudden and rapidly fatal illness of one of the cats that were fed the raw rabbit diet for 10 months was chilling and unexpected. The affected cat was diagnosed with dilated cardiomyopathy due to a severe taurine deficiency. Moreover, 70% of the remaining raw rabbit diet fed cats, which appeared outwardly healthy, also had heart muscle changes compatible with taurine deficiency and could have developed heart failure if continued on our raw rabbit diet. For the remaining three months of the study, the raw rabbit diet was supplemented with taurine and taurine levels returned to normal.

So other than stool firmness (and possibly coat "quality"), no health benefits were found for the raw diet (the study was very limited in its scope, though). However, despite having assayed the raw diet and found it met nutritional requirements, in actual use the raw diet turned out to be deficient in taurine, resulting in the death of one of the cat test subjects.

Further discussion will be coming, but this is clearly a cautionary tale for anyone designing their own raw diet (without the ability to assay it even).