You might hear that feeding over the suggested liver amount of about 5% of the overall diet is a recipe for vitamin A toxicity, but this is grossly exaggerated and misunderstood. The fact is that you’d have to feed a ridiculous amount of liver to achieve toxicity, but “because I say so” has never been good enough for me, I’d imagine it isn’t for you. Let’s explore this.
One of the fun things about figuring out nutrient requirements and safe upper limits is that no two sources can ever seem to agree on numbers, and new discoveries are always being made which affect recommendations. The following numbers and figures are an amalgamation of figures from several different sources and publication years unless specifically stated (including the NRC and AAFCO), which are all listed at the end of this post. The point is not to provide exact figures, but to illustrate that you don’t need to be all that concerned with vitamin A toxicity if you’re doing things with a lick of common sense.
Let’s use the theoretical example of a 50 pound dog who eats 3% of his body weight per day in raw food. This is a pound-and-a-half of food per day. According to the NRC and AAFCO, this dog requires between 1,100 IU and 3,000 IU of vitamin A per day minimum to maintain health, with other sources recommending more than that as ideal. (e.g., Danish scholar and raw food advocate Mogens Eliasen suggests about triple the NRC minimum RDA and abut 30% more than the AAFCO RDA as ideal — up to about 4,540 IU for our example dog.)
What we’re concerned with is toxicity though — enough to actually hurt or kill a dog. The “safe upper limit” of vitamin A for our example dog is in the neighborhood of 50,000 IU, which is to say that even if you regularly fed that much it would not actually do noticeable harm, but above that it is believed that risk could start. According to the Merck Veterinary Manual, “When vitamins A and D are ingested in large amounts (10–100 times daily requirement) throughout a period of months, toxic reactions may be seen.” I’ll repeat that for emphasis: Ten to one hundred times the daily requirement throughout a period of months.
To put this all into perspective, depending on who you ask (WAPF or NutritionData/USDA, with there also being an established discrepancy based on what the cow itself has been eating), 100 grams of beef liver contains anywhere from about 17,000 IU to 35,000 IU of vitamin A. (That’s a big discrepancy, and another reason why being overly concerned about numbers is pretty useless unless you have very solid data about the actual items you’re feeding at any give time!)
At 5% of the overall diet, our example dog is eating an average of about 34 grams of liver per day, which would be 5,780 IU on the low side and up to 11,900 IU on the high side for beef liver. As you can see, overall that’s actually pretty high given even the highest estimated requirement, but well within our established safe zone and not coming anywhere near the “safe upper limit”. Even the high possibility of 11,900 IU is only about a quarter of the safe upper limit. In order achieve the threshold of the safe upper limit, our example dog could be fed 150 – 200 grams of beef liver per day every day for months and likely still be fine from the perspective of vitamin A toxicity. That is about one-third to almost one-half of the total diet, and even that is just where higher risk might begin.
I want to mention in support of feeding a variety of livers from different animals and sources that chicken liver would come in at about 3,774 IU for our example dog’s daily 34 gram serving, lamb liver 8,364 IU, and pork liver 7,378 IU. Turkey liver is very high in vitamin A with the serving contributing about 9,146 IU of vitamin A! Arctic marine animals are famous for having a lot of vitamin A stores in their livers, but even if you had regular access to walrus liver, that 34 gram serving would contain about 27,600 IU of vitamin A, which is just over half of the ‘safe upper limit’. Maybe not the best idea to feed regularly, but for the sake of our argument even walrus liver as a full 10% of the diet would be just hovering around that safe upper limit mark.
The Waltham Centre For Pet Nutrition (an entity owned by Mars, makers of some of the kibbles you love to hate, but we’ll consider their findings anyway) has established a safe upper limit for puppies at 100,000 IU per kcal fed, which in raw food terms would be approximately 67,000 IU per pound of food fed daily, or 200 grams of beef liver for every pound fed! In other words almost HALF of the total diet in beef liver over an extended period of time, and that’s still the “safe upper limit” — not recognized to cause harm. That’s pretty much the same figure as the one produced with NRC figures for adult dogs. For cats the figures are similar too.
So, as you can see, no matter which figures you use or what you’re feeding, it would be virtually impossible to impose vitamin A toxicity via a raw diet, especially one fed in an informed and responsible manner. While figures of about 5% of the overall diet or approximately half of all organ matter fed are reasonable from a nutritional angle (vitamin A is not the only nutrient in liver — just the topic of this post), when it comes to vitamin A at least, even feeding much more liver or vitamin A rich foods than that would still not pose threat of poisoning or death from vitamin A.
Resources used in this post, and interesting further reading:
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