This is the second post about organs. if you haven’t seen it already, please visit What Is Classified As Organ? In that post the distinctions between organs and other tissues were covered, as well as why raw diets need organs, and a list of organs. In this post I’ll provide a synopsis of individual organs and discuss what role parts and pieces can or should play in the diet.
In the following descriptions you’ll come across suggestions to look up the breakdown of nutrients for yourself, which I highly recommend doing. The same organs from different animals may have general similarities, but also variances when it comes to nutrient qualities and densities — too much to detail here. You can use either (or both) NutritionData and/or USDA Food Composition Databases and search for specific items. If you’d like to browse I’ve provided a link at the end of the post.
LIVER — The quintessence of the organs and a MUST HAVE no matter what is liver. If you’re coming from a prey model angle, this organ is very large by volume and weight compared to the other internal organs. (It’s not the biggest — stomach and lungs are bigger, but more on that in a minute.) Observations of wild animals show that the liver is not only eaten, but often chosen among the first morsels to be eaten after a kill (link to page with sources). If you take a look at the nutrients that can be derived from eating liver you can see why it’s important. Liver is a very nutrient dense organ, and it contains some vitamins that just plain don’t exist in significant concentrations in any other body part, even other organs. Liver should be fed in amounts of about 5% of the overall diet, which is to say about half of your total organ allotment. A bit more (within reason) is fine and likely a bit less is too.
You may have heard about liver and the possibility of vitamin A toxicity. Information about this is on a separate page: The Reality of Vitamin A Toxicity. In short, you really don’t have to worry about it as long as you’re feeding a reasonable amount of liver.
KIDNEYS — Kidneys are also nutritionally important. From a prey model angle you can see that they aren’t present in the size/weight proportion that liver is, but they’re significant. (Plus there’s two — ‘one for me, one for you’ in the wild animal world I like to imagine, but our lucky dogs can have ’em both!) If you look at nutrient break-downs you’ll notice the kidneys are very good sources of some minerals that, again, are more highly concentrated than in other body parts and should be fed to raw-fed dogs and cats.
SPLEEN — Spleen is a sort of “grey area” organ. It’s significant in size, but not quite the overall nutrient powerhouse that liver and kidneys are despite its similarity in appearance: dark, reddish purpley, and squishy — with it’s weird mottled surface I call it ‘alien autopsy’. It is incredibly high in iron and contains a lot of vitamin C when it’s fresh — not a trait of liver or kidney. Spleen is an excellent addition to raw diets, but not absolutely crucial.
PANCREAS/THYMUS — These organs are functionally different and from different areas in the body, but you’ll find them both available as “sweetbreads”, either combined or separate. We are now into the organs that are solidly ‘optional’. Like other organs, this organ/gland duo packs a good vitamin and mineral punch, so why not use them in moderation when you can find them? From a prey-model perspective they’re relatively small and pretty fatty (a good thing if not overdone), so they should be more “sometimes” foods. On the flip side, if you cannot find them you do not need to worry about the balance of your raw diet!
BRAIN — Brain is another food that has some nutrients presented in a way that plain ol’ muscle meat and bones do not, but is hardly a “must” in the diet. In natural prey animals the brain is really not very significant in weight compared to overall body weight. (I know a cow is not really a natural prey animal, but I’ve been wanting to regurgitate this statistic for years: Did you know a cow’s brain only weighs about a pound? For an animal that can weigh 1,500 pounds that’s not a lot of grey matter!) Again, good from a variety standpoint. Feed in moderation if it’s available.
ALL THAT OTHER STUFF: Now we get to the “other” organs. These are the ones most people say to feed as “meat” instead of “organ”. Are they necessary? Probably not, but there are some great reasons to feed them. One is price, another is just plain variety. There is definitely value in opening up the variety you can offer by feeding parts other than skeletal muscle. Skeletal muscle should make up the majority of the meat portion of the diet. I never tire of emphasizing the importance of meaty bones, but using the following organ systems as part of the meaty-meat part of your pet’s diet is a great way to mix things up, and can make raw feeding more affordable. Each part does have unique nutritional properties, so in the name of variety and fulfilling that “prey model” feed the weird bits too!
TONGUE — Tongue is a great piece of meat for dogs. Most people can find both beef and pork tongue easily. Depending on local tastes it can be really cheap or really expensive, though! Where I live pork tongue is moderately priced, but beef tongue is so so expensive I’ve never even considered it. Tongue is wonderfully chewy and presents a nice challenging meal for most dogs. It’s also more or less boneless, so a great item to offer when you need to eke out bony things like chicken parts. It is on the fatty side, so you’ll want to feed within reason and moderation. People usually favor different parts for different dishes; Sometimes you can buy the whole tongue, other times it’s just the front part. Either way it’s good eatin’.
HEART — Heart is a special muscle and there’s no other one quite like it in the body. Heart is not super special compared to skeletal muscle nutritionally, but it does have quite a bit more iron. It also has more vitamin B12 than skeletal muscle, but not more than liver or some of the other organs listed above. For some reason heart has the reputation of being high in taurine, but that level is actually moderate, and there are a lot of other cuts of actual skeletal muscle that have more. Because of the relatively high iron content, feeding in excess can cause loose dark stools. Heart can be a great inexpensive food, and it’s OK to feed in excess of what you might find proportionately in a prey animal, but it shouldn’t make up a wildly disproportionate part of the the diet. You see info being passed around that heart shouldn’t make up more than X% of the diet. Remember that these are guidelines, and there is no magic number that describes “safe” vs. “unsafe”. Use common sense and pay attention to the pet you’re feeding!
GIZZARD — (not found in mammals) — Gizzards are the muscles that surround a special sac in many bird species including chickens and turkeys (as well as some other animals), which function as a ‘second stomach’ in breaking down food. The part you buy for eating is a very tough muscle usually with quite a bit of connective tissue attached. The nutrient profile is not dissimilar to many skeletal muscle cuts, though higher in iron and selenium, and they have vitamin C. Like heart, gizzards can be fed in portions that would never be possible in nature, but keep it within reason. There is more about the actual structure and potential use of gizzards in photos and commentary on this page: Gizzard Goodness.
STOMACH (Tripe) — The subject of tripe is covered on its very own page. Please view that entry for more about feeding tripe: Tripe Hype
LUNGS — Lung is an interesting organ both in its nutritive properties and as a structure. (Buy it at least once just to examine for yourself as a point of interest in biology and physiology!) It’s not the most common thing to find, but it is available, and is worth getting from time to time. Fresh lung is actually very high in vitamin C compared to a lot of other body parts, save spleen, which it is on par with. It also contains about as much iron as most of the organs listed in the first part, which is to say far more than ‘regular’ muscle meats. Given lots of vitamin C and iron, large amounts in a sitting can cause loose stools. It can be deceptive — hunks of lung look and feel like a wet pink marshmallow, which you assume is kind of like filler, but it’s nutrient dense! Like many other items in this category, lung can be fed regularly, but shouldn’t be fed to the exclusion of meaty bones. A ‘sometimes’ food for sure.
TRACHEA/ESOPHAGUS (GULLET) — The trachea and esophagus are the ‘wind pipe’ and the ‘food pipe’ respectively — tubes that connect the head to the thorax and abdomen. They are pretty unique structures in that they are constructed from a lot of specialized tissues. Despite not having actual bone they are very rigid, which is due to the cartilaginous properties of the organs. Cartilage is a connective tissue, which literally boiled down results in gelatin. While nutritive, cartilage is not an ideal source of protein or vitamins/minerals. There is also smooth muscle present (different from skeletal muscle), but not enough to really be appropriate as a protein source. These ‘pipes’ make for a fun chewy meal or snack for a dog or cat, but would only make up a “meal” in as much as the rest of the chunk of animal that they’re attached to.
LYMPH RELATED TISSUE — The lymphatic system in any body — regardless of species — exists to transport lymph fluid around the body. Lymph fluid serves many important functions. When you think of a liquid in a body, you probably think “blood”, but lymph makes up a large part of it, though clear and unremarkable. There are also lymph nodes, which are blobby structures that are part of the immune system and serviced by the various vessels that carry lymph around the body. I don’t know anywhere that you can actually buy lymph tissue as a food item specifically, but I wanted to mention it in the name of being thorough. When you get a whole animal you might see a bunch of tissue that’s unrecognizable — definitely not the the larger more common “food” items. This might just be something you don’t recognize, it also very well might be lymph tissue. It’s all fine and good for your pet to eat, though somewhat unclassifiable, and will likely just be counted in with ‘meat’ weights.
SALIVARY AND HORMONE-SECRETING GLANDS — There are several glands within the body that, like lymph tissue, are probably not something you’re going to cut out of a whole animal or larger cut and declare “food”, but know that they’re in there. I’ve seen photos of salivary glands sold as cuts of ‘meat’, but I have no idea if there are any unique nutritive qualities. Of course these would be found in whole tongues. Go ahead and feed all the blobby goodness! Not everything has to be some nutrient-packed food powerhouse.
PENIS — Most dog owners at this point have at least seen “bully sticks” for sale at pet stores, and know what they are. You might see raw “pizzle” for sale at ethnic and specialty markets. Some folks like dehydrating their own ‘bully stick’ treats, others will serve it raw. This is one cut that I, personally, actually have never seen for sale raw, and haven’t actively sought. Penis is primarily vascular tissue, which is to say from a nutritional angle comparable to cartilage or tendon. Actual nutrition breakdown information is scarce, but I’m willing to put forth that if you happen to see some for sale, pick it up just for the novelty if you like, but — like other not-so-meaty non-RMB items — feed sparingly.
TESTICLES — There are many raw feeders who regularly feed testicles, which go by many other names and clever euphemisms. I, personally, am not one of them. (For a while I could buy cases of lamb “fries” through my raw food buyer’s group, but they were expensive, so I put my money towards more valuable food.) Some raw feeders even give them the nutritional status of other ‘actual’ organs and do not feed them as just another source of boneless meat. Testicles are actually reasonably popular as food that people eat, too, but for all the popularity there is no nutrition information on either the USDA nutrient database or NutritionData. Internet hunting reveals that I am not the only one who has searched for reliable nutrient info, but has been left hanging. The info I was able to find (see links at the end of the post) reveal that testicles are comparable to cuts of muscle meat in protein, fat, and calories. By weight they contain quite a bit of cholesterol, but still not even close to what brain has, and about the same as lung. As specialized organs, they are bound to confer micronutrients and other biologically active compounds that might not be present in similar concentrations in other meats or organs, but without concrete data I am not going to make those kinds of leaps. I have heard anecdotally that they’re a good source of zinc and selenium, however it’s always necessary to remember that “good” as a qualifier is relative. Another blog cites an academic journal from 1965 [abstract here, I’m not paying the $40 to verify — I’ll leave that up to you], that has a bit more nutrition info about testicles — apparently the most to be found, as the cite is all over diet blogs. It gives an amount of zinc that is merely so-so. The zinc content from the study is out-done by beef liver by four times. Further, there is more zinc in some muscle meat cuts than there is in liver, so there you have it. That said, testicles are — according to this blog — especially potent food source of the enzyme hyaluronidase. Whether or not this is particularly useful is up for debate, but it is a good argument for feeding every bit of an animal in some quantity, even if it’s just small amounts not very often.
To sum up on the testicle thing — I do not see a lot of evidence that testicles are nutritionally potent in amounts to warrant status as an organ on par with liver, kidney, brain, etc. Feed infrequently or not at all.
UTERUS AND OTHER FEMALE REPRODUCTIVE SYSTEM PARTS — The uterus is an organ found in female mammals and birds, though the structures in various species differ in function. Uterus is one of those ‘meaty’ parts that has a so-so nutritional profile and can definitely be fed as a “sometimes” food, but shouldn’t be fed disproportionately to muscle meat. (A link to a nutrient breakdown of pork uterus can be found in the resources list of URLs at the bottom of the post.)
Ovaries are the female gonads (testes are that of the male), but quite small in the grand scheme of things. The chances are that you’d find ovaries on their own for sale as food would be slim, but they would be present in whole prey. Of course there are other tissues (mostly connective and fatty) — both male and female — belonging to the reproductive system that would, again, likely be fed as part of a whole prey items, but aren’t really worth considering as individual parts.
SPINAL CORD AND OTHER NERVOUS TISSUE — Feeding nervous system tissue is a rather highly debated practice, as prion diseases like “mad cow” and other transmissible encephalopathies (conditions that affect the brain and are contracted from an outside source) can be transmitted via the consumption of nervous tissue from affected animals. There has been evidence produced that dogs are resistant to contracting prion diseases (source), but some people still choose to play it safe and avoid nervous tissue as food. (Precautions could serve to inhibit the cycle of prion disease spread, so it’s not a bad idea at all to avoid feeding and properly disposing of certain items from infected animals even if your dog won’t get a canine version of “mad cow disease”.) Like many other items appearing at the end of this food list, aside from brains you’re unlikely to find nervous tissue as a food item separate from meat and bones, and individual nutritional analysis is not readily available. In most cases feeding things like neck bones that will contain spinal tissue is a safe and perfectly healthy practice. It’s not so much one of nutrients, as it is the fact that items containing larger areas of nervous tissue are valuable food items on the whole.
EYES AND OTHER SENSORY ORGANS — Eyeballs are one of those novel items that you might have available to you, as they are a part of many ethnic cuisines. Nutritionally they’re nothing spectacular, but do have a fatty component, and have a nice DHA/EPA load. If you want to feed them sparingly, go for it, but they are really more of an “extra” than a solid meaty portion of the diet. Other sensory tissue is most likely to be very much tied in to muscle and connective tissue.
SKIN — You’ve heard that “skin is the largest organ”, and that’s totally true! Skin is not fed as an organ, however, and you’ll want to feed it as part of your “meat” allotment, not as a separate entity. Even though an animal’s skin is large in surface area, it’s not really all that major by volume, and skin should be fed as part of what it is attached to more than as a food item on its own.
Skin is made up of layers, and when we consider it from a nutritional point of view it usually includes the layer of subcutaneous (under the skin) fat, which is why you might associate skin as being “fatty”. The outer layer of skin is made up of epithelium and keratinocytes — specialized cells that form the protective layer that shields the tissues under it from the outside world. The layers below for all practical purposes are connective tissue, and interspersed with glands that are too small and integrated to talk about separately. The skin of mammals is covered in fur or hair, which may or may not be fed as well. Many people remove the skin from food items fearing the fatty layer, which can be a useful tactic given an animal that should avoid relatively large portions of fat for health reasons like tendencies towards pancreatitis. If your pet’s health or constitution does not require special care to avoid fat, go ahead and leave the layer of skin and fat on. Fat is an important component in the diet of a carnivore. Most food animal skin is nice and thick and chewy, giving a great work-out to the pet who has to chew through it to get to the good muscle meat underneath. Pig skin, especially, is a great food item for ‘flossing’ and polishing teeth as a dog or cat eats it.
Coming soon! Part 3 in the discussion of organs: The practical side of feeding organs — How to feed organs (Mash ’em? Mix ’em? Feed ’em whole? Daily or weekly?); what to expect from the other end (Decipher and avoid the commonly associated “splarts”); and how to generally best get that 10% into your pet!
Outside links related to food, nutrient requirements, and feeding. Please copy and paste URL into your favorite internet browser.
Merck Manual: Nutritional Requirements and Related Diseases of Small Animals:
A list of links to NutritionData pages for organs:
Resources used in this post. All accessed by the author in the writing of this post, June 2017. Please copy and paste URL into your favorite internet browser.
General info on Vitamin A:
More info on Vitamin A:
Vitamin A, animal specific:
A blog that has the 2006 NRC required nutrients for dogs published in a simple format:
Nutrition information on testicles from the WAPF:
More regarding nutrients and testicles:
Nutrients in pork uterus:
Information about dogs and prion-disease resistance:
Nutrient info for caribou eyeballs:
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