Why Hearts Have Higher Taurine
If you are a dedicated cat parent who wants keep your kitty as healthy as possible, you've likely already read about the benefits and necessity of feeding your little feline food containing taurine. Furthermore, you may already know that turkey hearts, chicken hearts, and duck hearts are exceptionally high in taurine. What you probably don't know, however, or know in detail, is why this is true. Why are hearts so high in taurine? We answer this question in detail below and we also explain why bird hearts have more taurine than most mammalian hearts.
A Bit Of Relavent History
On August 14 1987, the Los Angeles Times reported that tens of thousands of domestic cats had died from heart disease due to a nutritional deficiency in commercial brand cat foods. Specifically, these beloved feline members of American households had died from dilated cardiomyopathy (DCM) due to the lack of taurine. Basically, their hearts became too weak to meet their metabolic demands.
Cat lovers were understandably shocked and dismayed by this startling revelation. With the spotlight now on this issue, Purina and other major cat food manufacturers quickly reformulated their commercial cat foods to contain taurine. However, there has been ongoing concern ever since over the quantity, and perhaps more importantly, the quality of the taurine in highly processed commercial cat food. As a result, many cat parents look for ways to supplement their cat's diet with healthier and more trusted sources of taurine. Feeding their cats raw hearts as a highly nutritious treat has become a popular way to ensure they are getting enough taurine.
The timing of the Los Angeles Times' article was spurred by a scientific research article published in the top-rated journal Science that same month in 1987. However, this national attention addressed an issue that had actually plagued domestic cats since at least the 1970s. It had been known in the scientific community since the 1970s that a lack of taurine in a cat's diet can cause retinal degradation, often leading to blindness. In fact, kittens born to cat mothers deficient in taurine can be born completely blind! However, even though the cat food industry had been aware of the taurine issue since at least 1981, they failed to add taurine to their cat food formulas until they received national media attention.
The Hardest Working Muscles Contain the Most Taurine
In general, the harder a muscle works, the more taurine it contains when eaten as food. The hardest working muscle in the body by far is the heart... no other muscle even comes close! Therefore, the heart contains the highest concentration of taurine! Following this same "rule," skeletal muscles that get worked harder contain more taurine than skeletal muscles that don't get used as much. In birds, the dark meat corresponds to the skeletal muscles that get worked the hardest, and therefore, they contain more taurine than the white meat.
Just How Hard Does a Heart Work?
To give some perspective on how hard a heart works, a human heart pumps a minimum of 2500 gallons of blood a day, according to the University of Chicago Medicine. Furthermore, a human heart beats about 115,000 times a day, about 42 million times a year, and about three billion times over the course of a lifetime! This is non-stop work all day every day until you die! Bodybuilder biceps pale in comparison!
What's even more amazing to consider is the fact that the hearts in certain other animals, namely birds and mice, actually work much harder than the human heart! Compare the resting heart rate (beats per minute) of the various animals listed below:
Adult Chicken: 250–300
Chick (baby chicken): 350–450
Domestic Turkey (Broad Whites): 298-309
Tufted Duck (a diving duck) Floating On Water: 260
Common Pochard (a diving duck) Floating On Water: 158
Dairy Cow: 48–84
The Higher the Heartbeat the More Taurine the Heart Contains!
Across all animals, there is a direct correlation between how fast the heart beats, i.e. how hard the heart works, and how much taurine will be found in each gram of heart tissue! This is because a faster beating heart needs more taurine than a slower beating heart to function properly. There's also more taurine in the skeletal muscles of animals with higher heart beat rates. This makes sense because animals that have a higher metabolic rate need a corresponding higher heart rate.
Looking at the heart rates above, you will notice two particular standouts: rodents and birds! This is why there is so much taurine in rodent and bird hearts, and of course, rodents and birds (and bugs) just happen to be the favorite foods of most frisky felines!
Birds have an extremely high metabolism, even at rest, and therefore have a heart that beats very fast and is exceptionally high in taurine. Birds also often engage in activities over an extended period of time that require their hearts beat even higher than a mouse. For example, if you've ever watched ducks on the water, you know they can be very energetic beasts! Dabbling or diving for food, diving to escape danger (eagle or human approaching), and taking off in flight from the surface of the water all require a tremendous amount of energy. Duck hearts are designed to handle these intense bursts of energy and their heart rate can skyrocket in mere seconds! In fact, ducks give new meaning to the old expression, "working your heart out!"
In 1979, there was a very interesting experiment conducted with Tufted Ducks and Common Pochards, two types of diving ducks. This experiment clearly illustrated just how fast a duck's heart rate can escalate when they dive. It also showed that even at rest, ducks have an exceptional high heart rate. To collect their data, the scientists surgically implanted a radio transmitter inside the ducks that would constantly record their heart rate and respiratory rate. They then allowed the ducks to roam free within a 20 meter x 20 meter range (one meter equals 1.09 yards) and observed their behaviors while receiving heart rate data.
Just before a spontaneous dive, Tufted Ducks went from an average heart rate of 260 beats per minute to 395 beats per minute! This astounding increase in heart rate was accomplished in only a split second! Common Pochards went from a heart beat of 158 beats per minute to 285 beats per minute. Usually too, the ducks would dive several more times before their heart rate returned back to where it was before the first spontaneous dive so this incredibly elevated heart rate was sustained for a long time. When diving specfically for food, the heart rate went up even more. When being chased by a "predator," in this case a human with a big net, the Tufted Ducks' average heart rate went up to 532 beats per minute and the Common Pochards' average heart rate went up to 482 beats per minute. These ducks are true olympians!
Since ducks can double their already exceptionally high resting heart rate within a few seconds, they have to store plenty of taurine inside their heart tissue to accomodate these herculean feats! This is also why duck skeletal meat is so dark. Remember, the darker the poultry skeletal meat, the more taurine it contains. Even slower birds, like chickens and domesticated turkeys, have very high metabolic rates due to their heritage and their continued need to be able to produce a great burst of energy for flight and other activities like escaping eagles and foxes coming into the barn yard!
Relative to their body size, birds also tend to have a larger heart than mammals and they pump out more volume of blood with each beat. As you can see from studying the heart rate data above, mice and other rodents are a major exception to this trend. This is because rodents are exceptionally energetic compared to other mammals, and therefore, have an exceedingly high heart rate, high metabolism, and copious amounts of taurine stockpiled in their tissues.
What Does Taurine Do Inside the Heart?
Over the last few decades, it has become abundantly clear that taurine plays a key and integral role in the transport of positively charged calcium ions in the heart. Taurine also plays an equally important role in controlling how sensitive heart cells are to the calcium ions they encounter. In other words, taurine plays a pivotal role in the normal functioning of the electrical system of the heart. In performing this crucial role, taurine can be thought of as the master switch for one of the most fundamental elements of life: the heartbeat!
Without an adequate supply of taurine stored inside each heart cell, the heart will fail to beat properly. This was suspected by many scientists long before it was absolutely proven. Moreover, this is now a well-proven scientific fact. If taurine levels fall too low, heart contractions may become too weak to supply the body with the oxygenated blood it needs to flourish and too weak to remove toxins. It has also been proven that an irregular heartbeat can be induced by reducimg taurine and this same irregular heart beat can then be cured by restoring taurine back to normal levels. Further, the outer and inner membranes of each heart cell will deteriorate without proper taurine levels.
Taurine is so important to the normal functioning of the heart, it is stored in great quantities inside a membranous structure called the sarcoplasmic reticulum inside each heart cell. However, the exact mechanisms by which taurine controls the life-giving tasks are not entirely understood yet, even by the scientists actively studying these biochemical reactions. However, this is an area of very active scientific research because taurine supplementation (or increased taurine in diet) is thought to hold great promise in preventing, and even reversing, many heart disorders, diabetes, and other common life-compromising ailments in both people and pets. Look for taurine to become an increasingly important part of the conversation in health conscious circles, natural pet forums, and in the medical/veterinary community.
Cats Instinctively Hunt For Taurine
All members of the cat family, from the smallest member to the largest member, are instinctively drawn to hunt for prey that contain high levels of taurine and/or they prefer to eat the parts of their prey that have more taurine.
When big cats like leopards make a kill, they almost always eat the heart first! When lions hunt in groups, the socially dominant members eat first and they almost always start with the heart. This is usually followed by eating other internal organs high in taurine like the liver and lungs. Only then do they move on to the skeletal muscle meat, and here too, they show a clear preference for skeletal muscle meat that contains the most taurine. Again, muscles that work the hardest contain the most taurine so they usually eat the romp and hind quarters before they eat less worked skeletal muscles. This way, if they get chased off by hyenas or disturbed in any other way, they will have eaten the parts of the prey that contain the most taurine.
For survival purposes, smaller cats like wildcats are instinctively drawn to prey items that contain the most taurine. These include mice, rats, birds, insects, scorpions, and marine arthropods like shrimp and crab when available.
When food is limited, cats will eat an entire mouse head first, tail and all. They will also eat an entire bird when food is less abundant, except perhaps the beak and largest feathers of the wing. However, when food is plentiful and/or they aren't very hungry, small cats have a tendency to eat the parts containing the most taurine and leave the rest! This includes the heart, the head (because brain and eyes are exceptionally high in taurine), and other internal organs. This is why so many people find partially eat corpses around if they have outdoor cats, most often with the heads and/or the heart missing!
Cats instinctively target taurine in their hunting strategies -- and the heart is their #1 prime target across all species of cats, big and small! This is because hearts have more taurine! To optimize your companion cat's health, feeding them raw hearts to mimic what what wild cats target in nature, is always an excellent option. To learn more, you can read our article on why raw hearts are better than cooked hearts.
THOMAS H. MAUGH II. Thousands of Cat Deaths Traced to Pet Food Deficiency. Los Angeles Times. August 14, 1987.
Pion PD, Kittleson MD, Rogers QR, Morris JG. Myocardial Failure In Cats Associated With Low Plasma Taurine: A Reversible Cardiomyopathy. Science 1987; Aug 14;237(4816):764-8.
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.
Merck Veterinary Manual. Online Edition Revised March 2012.
L. M. Krista, Ray E. Burger and P. E. Waibel. Blood Pressure and Heart Rate in the Turkey as Measured by the Indirect Method and their Modifications by Pharmacological Agents. Poultry Science (1963) 42 (3): 646-652.
P. J. Butler AND A. J. Woakes. Changes In Heart Rate and Respiratory Frequency During Natural Behavior of Ducks, With Particular Reference To Diving. J Exp Biol 79, 283-300.
Harris Ripps and Wen Shen. Review: Taurine: A “Very Essential” Amino Acid. Mol Vis. 2012; 18: 2673–2686.
Stephen W Schaffer, Chian Ju Jong, Ramila KC, and Junichi Azuma. Physiological Roles Of Taurine In Heart and Muscle. J Biomed Sci. 2010; 17(Suppl 1): S2.
Laura Della Corte, Ryan J. Huxtable, Giampietro Sgaragli. Taurine 4: Taurine and Excitable Tissues. 2006.
James J. Kocsis, S.I. Baskin, Stephen W. Schaffer. The Effects of Taurine on Excitable Tissues: Proceedings of the 21st Annual A. N. Richards Symposium of the Physiological Society of Philadelphia. 2012.
Michelle T. Bernard. Raising Cats Naturally: How To Care For Your Cat the Way Nature Intended. January 1, 2003.