In a previous article, we gave a detailed scientific explanation for why hearts are one of the best sources of taurine you can feed your cat, dog, or ferret. In particular, bird hearts like turkey hearts, chicken hearts, and duck hearts have more taurine than the hearts of most other animals and we explained why this is so. In this article, we will explain why raw hearts are a better source of taurine than cooked hearts. We will also explain why raw meat in general is a better source of taurine than cooked meat.
Companion cats are essentially domesticated African Wild Cats! As such, their physiology functions basically the same. This means they are obligate carnivores and need a diet of mostly animal meat and internal organs to survive and thrive. Moreover, they need quality food containing taurine that is bioavailable or they will develop serious health issues. Feeding raw hearts daily, or at least weekly, can prevent these issues because taurine levels are exceptionally high in raw hearts, and equally important, taurine is more bioavailable in raw hearts than cooked hearts (see below for more information).
One of the most common health issues in taurine deprived cats is retinal degeneration which can quickly progress to complete blindness. Another medical problem often seen in cats with low a taurine diet is dilated cardiomyopathy. This is where the heart muscle, starting in the left ventricle, becomes too weak to pump blood properly. Dilated cardiomyopathy does not always show obvious symptoms until it is too late so many cats die from it. This heart disease can also occur in dogs and ferrets if their diet is too low in taurine, especially as they age. Low taurine causes many other health issues as well including reproductive failure, decreased kidney function, decreased motor function, and a compromised immune system.
According to the latest (2006) "Nutrient Requirements of Dogs and Cats" report by the National Research Council, a division of the National Academy of Sciences, the minimal safe blood plasm concentration of taurine in cats is 40 nm/mL. This recommendation is based in part on studies that show cats with dilated cardiomyopathy often have taurine levels below 40 nm/mL in their blood plasma. It is also based on the fact that dilated cardiomyopathy can be induced in cats when they are intentionally fed a diet that allows their blood plasma taurine levels to fall below 40 nm/mL. This minimal 40 nm/mL blood plasma taurine concentration is substantiated in numerous other academic references. However, many experts now recommend an even higher blood plasma taurine level, 50-60 nm/mL minimum, to maintain optimal health in cats.
Several experiments have been performed that compare the effect of cooked cat food versus raw food on a cat's blood plasma taurine levels. These experiments clearly show that raw food (previously frozen) easily maintains adequate taurine levels in the blood plasma while heat-processed canned food does not (commercial cat food). Two of the best of these experiments were conducted by a team of scientists in the School of Veterinary Medicine at the University of California at Davis and published in peer reviewed journals. They have also been re-tested so the results can be trusted.
In the UC Davis taurine experiments, the taurine blood plasma concentrations are compared between cats fed a heat-processed can cat food versus a raw food (previously frozen) with the same exact ingredients. Besides the variation in how their food is processed (cooked versus raw), the cats tested are kept in exactly the same conditions: same space provided, same constant temperature, same constant water, same 12 hours of light/day, same 12 hours of darkness/day, and same slight air currents. The experiment is set up this way to ensure that the difference in the food is the only variable, i.e. the only thing different between the two groups of cats.
The cooked cat food and raw cat food contain exactly the same ingredients: liver and meat by-products being the top two ingredients with some smaller amounts of ground corn, animal fat, and dried skimmed milk (12% crude protein total). In the cooked version, the cat food is preserved by heating it to 120 degrees Celsius (248 degrees Fahrenheit) and then canning it. This is similar to how all commercial can cat foods are preserved and made "shelf stable" so they can sit in a warehouse or grocery store shelf for years without spoiling. The raw food version was frozen to minus 20 degrees Celsius (minus 4 degrees Fahrenheit) after preparation. It was maintained at this temperature until it was thawed and fed to the cats receiving raw food.
The results were dramatic!
The taurine levels in the blood plasma of the cats fed the heat-processed diet dropped to only 5 nm/mL. This is well below the minimum required for good health by anyone's standard. On the other hand, the taurine levels in the blood plasma of the cats fed the raw diet averaged nm/mL! This is well above the minimum level needed to maintain good health.
It should be emphasized that even though the heat-processed canned food was supposed to contain adequate taurine levels for cats, in fact almost double the recommended amount for that year (1070 mg/kg dry matter determined by analysis), it was evidently processed in a way that the cats could not fully utilize it, i.e. it was not entirely bioavailable to the cats even though they were eating it. However, the taurine in the previously frozen raw diet, containing the exact same ingredients, was bioavailable and the cats who received this diet maintained healthy taurine levels, well above the threshold needed to survive.
By also measuring the carbon traced back to the taurine (by looking for carbon-14 they included in the taurine) in their respiratory carbon dioxide, urine, and feces, the scientists were able to study how a cat processes taurine from cooked food versus raw food. It was concluded that the taurine from the heat-processed food was not able to be absorbed fully by the small intestine, probably due to a substance being released in the cooking process that made taurine transport through the cell membrane difficult. They further deduced that the gut flora found in the large intestines broke down the taurine that was not absorbed in the small intestine into inorganic substances that were not useful to the cat and he or she simply defecated it out.
These experiments, as well as several others, clearly show that taurine becomes far less bioavailable when it is heat-processed in a manner consistent with how commercial cat food is normally processed. This is why pet food manufacturers often add synthetic taurine to their foods after they have been heat-processed, even when the food contains ingredients that are naturally high in taurine. On the other hand, these experiments also clearly show that subjecting taurine to freezing temperatures does not affect the bioavailability of the taurine significantly.
And.... this is the primary reason why raw hearts are better than cooked hearts! If you want to ensure your cat, dog, or ferret is receiving adequate amounts of natural bioavailable taurine in his or her diet, one of your best bets is to feed them freeze-dried hearts.
Hickman M.A., Rogers Q.R., Morris J.G. Effect of Processing on Fate of Dietary Taurine in Cats. J. Nutrition 1990; 120: 995-1000.
Nutrient Requirements of Dogs and Cats. Report By the National Research Council. Washington, DC: The National Academies Press, 2006
URL #1: http://www.nap.edu/openbook.php?record_id=10668
URL #2: https://books.google.com/books?
Gregory M. Douglass, Edward B. Fern, Androbert C. Brown. Feline Plasma and Whole Blood Taurine Levels as Influenced by Commercial Dry and Canned Diets. 1991; J. Nutr. 121: S179-S180,
James G Morris, Quinton Ray Rogers, Linda M Pacioretty. Taurine: An Essential Nutrient For Cats. J. Small Anim. Pract. 2008; 31(10):502 - 509.