Iron in a raw diet
In the article “what my cats eat in a day”, I showed you an example of 3 daily meals for my cats. I mentioned that I supplemented iron in that diet. Today, I’m going to go into more detail about iron, as it’s an essential mineral for cats. I will explain what iron is and its roles, how much iron your cat needs, in which foods you can find it, and more!
What is iron and its roles?
Iron is a mineral or–more precisely–a micromineral, also called a trace element because it’s present in the body in very small amounts: generally 0.005% of the body weight.
Iron is mainly a component of the protein molecule hemoglobin, which is found in red blood cells, but also of the protein myoglobin, which is found in muscle. They both have a role in the transport of oxygen. Iron is also a component of several enzymes in the body that are important for energy metabolism. [1][2]
Like in humans, an iron deficiency in cats will cause anemia and it manifests with lethargy, weight loss, pale mucous membrane, and blood in the urine or feces. Iron deficiency can happen because of blood loss, which is often caused by blood-sucking parasite infestation like ticks or fleas, or in case of injuries. Other symptoms of iron deficiency include a rough coat and decreased growth in kittens. [2][3]
Iron–like other microminerals–can be toxic when fed in excess: symptoms of iron toxicity include weight loss, liver dysfunction, and excess iron in the organs.
However, before reaching toxic levels of iron, a diet high in iron can have negative consequences such as reducing the absorption of zinc and copper. [2][3]
How much iron does your cat need?
Most studies on iron requirements have been made on kittens. The current NRC recommendations for kittens are the following:
A minimum requirement of 17 mg of iron per 1000 kcal, which is equivalent to 70 mg of iron per kg of dry matter (DM) for a 4000 kcal/kg diet. This minimum requirement has been established on a purified diet, without anything that could reduce the absorption of iron.
A recommended amount of 20 mg of iron per 1000 kcal, which is equivalent to 80 mg of iron per kg of DM. This requirement takes into account the lower bioavailability of iron in kibbles because of the presence of anti-nutrients such as fiber or phytate.
As the iron requirement of adult cats hasn't been studied, there is no defined minimum requirement, and the recommended amount is the same as the one of kittens.
In my opinion, it is safe to assume that the minimum requirement of kittens could also be used for adult cats which are fed a raw diet, as it contains highly bioavailable sources of iron and minimal anti-nutrients. [2][4]
There is no defined safe upper limit, as there isn’t enough research on the subject. However, there is a maximum legal content defined by the EU for pet food of 681 mg per kg of DM, equivalent to 170 mg per 1000 kcal. [2][5]
Where is iron found?
Iron is found in many foodstuffs such as meat and organs, but also plant foods like legumes, nuts, seeds, and leafy greens.
Unsurprisingly, as iron is mainly in the red blood cells, the richest food of all is blood, followed by spleen, and then organs like liver and kidney. You will find a table at the end of this article so you can compare the amount of iron in different ingredients.
However, there are two different forms of iron: heme iron, a kind of iron bound to heme proteins, and non-heme iron. [2]
Heme iron is found only in animal-based food, while plants contain exclusively non-heme iron. Meat generally contains around 60% of heme iron, this number varies with red meat like beef and veal containing up to 80% of heme iron and poultry containing only 40%. [6][7]
There is a lot of variation in the absorption of iron from 10% to 100% absorption! Heme iron is absorbed better than non-heme iron.
The absorption of non-heme iron is affected by many parameters. It is enhanced if the body's iron reserves are low, if the diet is high in iron, or in presence of vitamin C. Its absorption can be reduced by high levels of calcium, phosphorus, zinc, copper, as well as high levels of fiber like psyllium, presence of anti-nutrient like phytic acids, oxalates, and tannin.
On the other hand, the absorption of heme iron has been shown to be affected only by the calcium level in the diet. [2][8][9][10]
Do you need to add an iron supplement to a raw diet?
Even if meat contains more iron than plant foodstuff, the amount of iron in muscle meat is inferior to a cat's requirements. Most meat contains around 3 to 9 mg per 1000 kcal of iron, with only a few red meats containing more than 17 mg per 1000 kcal. While organs are richer in iron than muscle meat, if you can’t feed spleen the iron requirement generally isn’t met.
It could be argued that because the bioavailability of iron in raw meat is high, supplementation isn’t needed even if we are below the requirement. However, there is nothing in the literature to prove this assumption. Additionally, the amount of iron in whole prey is almost always well above the cat’s requirement, which makes sense as a whole prey would still contain blood and spleen. All this explains why when feeding a raw diet without these foods–like a PMR diet–the diet is deficient in iron. [11][12]
Example 1
Let’s consider a PMR recipe with a daily ration of 120 g, which is approximately 3% of Praline’s weight:
20 g chicken necks, 20 g beef hearts, 6 g beef liver, 6 g pork kidney, 12 g mackerel, and 56 g chicken breast.
The daily recommended amount of iron for my cat Praline (3.7 kg) is 4.8 mg, the minimum requirement would be 4.08 mg.
This diet contains 2.25 mg of iron which is only 47% of Praline’s recommended amount. If we consider the minimal requirement, the diet still covers only 55%. In that case, an iron supplement would be needed.
Example 2
In this second example, let’s consider another PMR recipe but with red meat:
27 g chicken wings, 20 g lamb hearts, 6 g chicken liver, 6 g lamb kidney, 12 g sardine, and 49 g beef chuck stew meat.
The diet contains 3.64 mg of iron which is 76% of Praline’s recommended amount and 89% of the minimum requirement. Even with red meat, the diet still covers only ¾ of Praline’s iron requirement.
However, if the 6 g of lamb kidney is replaced by lamb spleen, the diet would contain 5.77 mg of iron and the requirements would be covered.
How to supplement the diet of your cat?
As we have seen, the whole foods that are richest in iron are spleen and blood. If you can’t find them fresh an alternative would be freeze-dried or dehydrated spleen or blood, which are often easier to find.
If you can’t find any of these whole foods, the best alternative is to use a supplement. You will need to be careful when using iron supplements as excess iron can be dangerous.
Not all iron supplements are equal to each other depending on the form of the iron. Chelated iron (iron bisglycinate), which is iron chemically bound to an amino-acid, has a better absorption than iron salt like ferrous iron (Iron(II) ferrous sulfate, ferrous fumarate…) which are themselves better than ferric iron (Iron(III)). You’ll also need to pay attention to the iron amount in the capsule as it will vary from one brand to another. I generally recommend using the brand Solgar or NOW Food. [2]
Finally, some iron salt shouldn’t be used as they aren’t bioavailable like iron oxide or iron carbonate (iron oxide (E 172) is often used in pet food as a colorant to give a red, yellow or black hue). [2]
To conclude, iron is an important trace mineral that is often lacking in raw diets, as PMR diets aren’t perfectly recreating prey (missing blood and spleen). I recommend adding either dried blood or a chelated iron supplement to meet the iron requirement of your cat. You can use the calculator below to determine how much you should add to the diet.
Supplement calculator
This calculator is made using the metabolic weight formula:
The recommended allowance is 1.98mg per kg/BW^0.67 equivalent to 20mg per 1000kcal.
The minimum requirement is 1.7mg per kg/BW^0.67 equivalent to 17mg per 1000kcal
Iron in raw meat, organs, whole preys
| mg of iron / 100g as fed | mg of iron / 1000kcal | |
|---|---|---|
| Cut | ||
| Chicken breast | 0.37 | 3.1 |
| Chicken breast with skin | 0.74 | 4.3 |
| Beef chuck stew meat | 2.12 | 16.6 |
| Ground beef 10% | 2.24 | 12.7 |
| Ground beef 20% | 1.94 | 7.6 |
| Ground beef 30% | 1.64 | 4.9 |
| Beef brisket point | 1.69 | 6.3 |
| Lamb shoulder chop | 1.56 | 6.0 |
| Pork tenderloin | 0.97 | 8.1 |
| Pork leg shank | 0.69 | 3.6 |
| Turkey breast | 0.76 | 6.7 |
| Turkey thigh | 1.42 | 12.2 |
| Turkey thigh with skin | 0.77 | 4.8 |
| Veal escalope | 2.00 | 18.5 |
| Veal shoulder | 1.16 | 9.4 |
| Venison | 3.40 | 28.3 |
| Organs | ||
| Beef blood | 46.50 | 566.4 |
| Pork blood | 37.00 | 491.4 |
| Beef liver | 4.90 | 36.3 |
| Chicken liver | 8.99 | 75.5 |
| Duck liver | 30.53 | 224.5 |
| Lamb liver | 7.37 | 53.0 |
| Pork liver | 23.30 | 173.9 |
| Rabbit liver | 6.61 | 49.3 |
| Veal liver | 4.60 | 38.3 |
| Beef kidney | 4.60 | 46.5 |
| Lamb kidney | 6.38 | 65.8 |
| Beef heart | 4.31 | 38.5 |
| Chicken heart | 5.96 | 39.0 |
| Turkey heart | 3.70 | 26.4 |
| Beef spleen | 44.55 | 424.3 |
| Lamb spleen | 41.89 | 414.8 |
| Pork spleen | 22.32 | 223.2 |
| Veal spleen | 9.32 | 95.1 |
| Whole Prey | ||
| Mouse, neonatal <3g | 3.46 | 37.2 |
| Mouse, juvenil 3-10g | 2.80 | 23.1 |
| Mouse, adult > 10g | 4.51 | 26.3 |
| Rat, neonatal < 10g | 5.74 | 52.0 |
| Rat, adult > 50g | 5.02 | 23.2 |
| Quail 1 to 3d | 1.93 | 12.7 |
| Quail 21 to 40d | 2.76 | 18.0 |
| Quail >60d | 4.47 | 25.6 |
| Rabbit stillborn | 9.38 | 78.1 |
| Rabbit 30 to 45d | 5.03 | 35.3 |
| Rabbit >65d skinned | 5.87 | 34.6 |
Sources
[1] Linda P. Case et al. 2015. Canine and Feline Nutrition.
[2] National Research Council. 2006. Nutrient Requirements of Dogs and Cats. Washington, DC: The National Academies Press.
[3] Thatcher, Craig & Hand, M.S. & Remillard, Rebecca. (2010). Small animal clinical nutrition.
[4] Chausow, D G, and G L Czarnecki-Maulden. “Estimation of the dietary iron requirement for the weanling puppy and kitten.” The Journal of nutrition vol. 117,5 (1987): 928-32.
[5] FEDIAF (2021) Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs.
[6] Cross AJ, Harnly JM, Ferrucci LM, Risch A, Mayne ST, Sinha R. Developing a heme iron database for meats according to meat type, cooking method and doneness level. Food Nutr Sci. 2012 Jul 1;3(7):905-913.
[7] Lombardi-Boccia, Ginevra & Beatriz, Martinez & Aguzzi, Altero. (2002). Total Heme and Non‐heme Iron in Raw and Cooked Meats. Journal of Food Science. 67. 1738 - 1741.
[8] Baker, D H. “Comparative nutrition of cats and dogs.” Annual review of nutrition vol. 11 (1991): 239-63.
[9] Chausow, D. G., Czarnecki-Maulden, G. L. 1988. The relative bioavailability of plant and animal sources of iron to the cat and chick. Nutr. Res. 8:1041-50
[10] Fly, Alyce & Czarnecki-Maulden, Gail. (2000). Iron bioavailability from hemoglobin and hemin in chick, rat, cat, and dog: A comparative study. Nutrition Research - NUTR RES. 20. 237-248.
[11] Dierenfeld, Ellen & Alcorn, Heather & Jacobsen, Krista. (2002). Nutrient Composition of Whole Vertebrate Prey (Excluding Fish) Fed in Zoos. 7994.
[12] Kerr, K. R., Kappen, K. L., Garner, L. M., & Swanson, K. S. (2014). Commercially available avian and mammalian whole prey diet items targeted for consumption by managed exotic and domestic pet felines: macronutrient, mineral, and long-chain fatty acid composition. Zoo biology, 33(4), 327–335.
Sources for the table
USDA
CIQUAL
Kerr, K. R., Kappen, K. L., Garner, L. M., & Swanson, K. S. (2014). Commercially available avian and mammalian whole prey diet items targeted for consumption by managed exotic and domestic pet felines: macronutrient, mineral, and long-chain fatty acid composition. Zoo biology, 33(4), 327–335.
Dierenfeld, Ellen & Alcorn, Heather & Jacobsen, Krista. (2002). Nutrient Composition of Whole Vertebrate Prey (Excluding Fish) Fed in Zoos. 7994.