12/21/2021
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I know many of us horse owners and hoofcare providers have seen the conversations about iron in a horse's diet, and the potential effect on hooves. Before we get too into the nitty gritty of diet and the hoof, I want to back up and look at a horse’s needs, based on the NRC Requirements. Hooves are so often a reflection of the health of the animal, and to make sure a horse can grow the healthiest hoof possible, we need to make sure they are meeting all their nutrient and mineral requirements. Thank you to Dr. Gustafson for helping me understand this a bit better myself!
MINERALS IN FORAGE- are they sufficient?
From Dr. Gustafson’s database of hay testing, she found that out of 250+ samples of forages tested, 97.8% were deficient in zinc, 95.2% were deficient in copper, 12% were deficient in manganese, and 0% were deficient in iron. That means that just from hay, a horse could consume the daily requirement for iron, or sometimes far exceed it. On the other hand, horses rarely if ever meet their requirements for copper and zinc from their forage. That alone is a problem - one that grains and feeds rarely correct well, since so many horses can't handle or aren't fed the recommended daily amount of grains, often due to lower calorie needs or hoof issues preventing owners from feeding grains with sugar and starch above 10% combined. So horses are often walking around with frank deficiencies of minor minerals- copper and zinc to be exact.
But, many feed companies make a ration balancer to handle the caloric issue and they have a much more concentrated nutrients at a much lower feeding rate, you say! Sounds great, right? But here’s the catch: they often add iron, and sometimes a lot of it. We will talk about the issue with this in a second.
IRON AFFECTING COPPER AND ZINC ABSORPTION
On top of the fact that horses are walking around with copper and zinc deficiencies, the frank deficiency is worsened with a relative deficiency from iron - since we know that iron inhibits the uptake of copper and zinc. Dr. Piper Klemm has studied iron chelation extensively for her dissertation, and actually chatted with me on her podcast about why excess iron inhibits the uptake of copper and zinc in the body, and the horse has no natural way to chelate iron (other than bloodletting). Iron competes with copper and zinc absorption in the body, and copper and zinc are needed for healthy hooves.
BUT IS IRON REALLY ABSORBED?
Now, there are some groups that tend to say that iron isn't absorbed well or isn't bioavailable in various forms. While this would be wonderful- it just doesn't seem to work out well in practice. Aside from the fact that many hoofcare providers can show bloodwork on personal or client horses with high serum iron, TIBC, and ferritin, and have horses with diagnosed iron overload, article after article online shows how horses rarely if ever have an iron deficiency (in fact, iron deficiency anemia is almost unheard of in horses). So they are clearly getting their dietary iron from somewhere. One study linked below shows 22 equines on a property with high iron in the water, and each horse was found to have excessive iron stores and liver issues.
BUT ISN'T IRON REGULATED IN THE BODY?
Yes, hepcidin does regulate iron in the body, but unfortunately this can go awry if it is overwhelmed with excessive iron supply (Equine Applied and Clinical Nutrition, 2013). Couple that with the fact that horses with metabolic issues may also have problems with hepcidin and iron regulation, we can assume that not all horses are regulating iron properly.
DOES IRON CAUSE METABOLIC ISSUES?
In short- we can't claim that. And no one is trying to claim that. Let me explain.
Dr. Kellon and Dr. Gustafson published a study last year of hyperinsulinemia and hyperferritinemia in horses. They found that every single horse in their study, all hyperinsulemic horses, had serum ferritin that exceeded the reference range. They did NOT say that iron causes metabolic issues, or laminitis, though.
There is a CORRELATION between high iron and hyperinsulemic horses. I want to be clear that correlation does not mean causation so I’m not saying that high iron CAUSES metabolic issues, but it seems that metabolic horses may sequester iron, which can lead to a host of issues.
Another study in 2012 using horses (actually hoping to compare to rhinos) found the same correlation - high ferritin levels at peak insulin concentrations after dextrose administration. They even mention captive rhino diets are higher in iron, that the captive rhinos have more fat stores, and they are moving less. I’d say that is similar in domesticated horses compared to feral/wild. The issue here is hay is often high in iron, or at least not deficient in iron as Dr. Gustafson’s database mentioned, and some places also have high iron water, and then people will sometimes feed iron supplements or grain that has iron added. There is no "shortage" of iron in the equine diet. And we know that iron inhibits the uptake of copper and zinc, which is needed for healthy hooves.
SO WHAT CAN DO ABOUT THIS?
So what do we do for horses to ensure that they are getting all the minerals they need for a healthy hoof? Well, we know that feeding at least the NRC amounts of minerals is important for whole horse health and therefore hoof health, and often it can be a minefield, since feeding an excess of one mineral can affect absorption of another mineral. Dr. Kellon has a running field study (over 2 decades now) cataloguing owners practicing tight mineral balancing on metabolic horses, tracked on the ECIR online database of case histories. From there, we have seen that this mineral balancing over time, for example keeping an iron:copper:zinc:manganese ratio of 4:1:3:3, helps to balance for possible dietary iron excesses or at least meet mineral deficiencies, observed through hoof changes, bloodwork, and comfort over time. Many of us have seen a direct result of healthier feet, tighter white line, increased comfort, when doing this. I’m sure many of us could talk for hours about the improvements we have seen in feet when mineral balancing- anecdotally of course! And interestingly enough, there was a study in 1999 that even suggested that supplementing copper and zinc can help with the susceptibility to white line disease (Pollitt quoted this study in 2005).
Since the safe upper tolerable limits of copper and zinc are much higher than we would ever supplement, and since some hays almost hit the safe upper limits for iron, I'd say it's fairly cheap, easy, and safe to avoid added dietary iron and try testing hay (I use EquiAnalytical), and balancing copper and zinc in the diet. You just might be surprised at the results you see in the body, coat, and feet 😊
A few things to explore:
Iron issues in metabolic horses: https://pubmed.ncbi.nlm.nih.gov/32042647/
The rhino study, using an equine model: https://pubmed.ncbi.nlm.nih.gov/23156707/
Iron overload in horses: https://forageplustalk.co.uk/iron-overload-in-horses-by-dr-kellon/
Iron issues in water and liver issues:
https://beva.onlinelibrary.wiley.com/doi/abs/10.1111/evj.13029
Balancing copper and zinc to iron: https://www.hoofrehab.com/Diet.html
Podcast episode where Piper Klemm and I discuss iron and copper and zinc here: https://www.theplaidhorse.com/2021/10/22/plaidcast-252-michael-tokaruk-alicia-harlov-by-taylor-harris-insurance-services/
Podcast episode with nutritionist Scott Cieslar discussing iron and mineral balancing here: https://madbarn.com/videos/mad-about-hooves-scott-cieslar-on-nutrition-for-hoof-health-the-humble-hoof/
Podcast episode with Sally Hugg here, for more basic information: https://thehumblehoof.com/2023/08/08/nutrition-and-the-hoof/
I also have a webinar which spends 40 min on nutrition and the hoof here: https://youtu.be/RUKjGgoKnyw
This webinar includes case studies/pictures.
