Iron overload in horses: Is it a real problem?

Many people seem to worry iron overload in horses. They even seem to worry about iron overload in other people’s horses.. I don’t know enough about the topic, so I asked various experts in related fields if they would be willing to answer some questions.

Three people generously agreed to share their knowledge. Each brings a distinct perspective that reflects their experience and expertise, and they were invited to answer my questions as best they saw fit.

Is iron overload a real problem? You decide, after reading the information below, and doing some more investigating if needed. Further information is available on their sites and links provided below or on the Facebook groups Equine Wellness and Nutrition Group and ECIR Group – Equine Cushings and Insulin Resistance.

Table of Contents

Meet the experts
What are the signs of iron overload in a horse?
Are there any tests your horse can undergo to confirm excess iron?
What about forage? Do you recommend testing your grass and/or hay?
What should we look for in forage and other feed content?
How should we compensate for excess iron content in forage?
Is there any feed you would recommend?
What about any feeds you would advise us to AVOID for certain horses/scenarios?
Is there anything else you would like to say? 

The experts:

Eleanor Kellon, VMD

Dr. Eleanor Kellon attended the University of Pennsylvania School of Veterinary Medicine, graduating magna cum laude in 1976. An expert on equine nutrition, she is an authority on use of nutraceuticals in horses. Currently a veterinary specialist for Uckele Health & Nutrition, Dr. Kellon owns Equine Nutritional Solutions and the Equine Cushing’s & Insulin Resistance Group. She has authored eight books and numerous academic papers as well as writing for the popular press.

David Ramey, DVM

Dr. David Ramey is a 1983 graduate of Colorado State University.  After completing an internship in equine medicine and surgery in 1984 at Iowa State University, he moved to southern California, where he established his own practice in 1987.  Dr. Ramey is the author of 13 books on horse health, over 70 scientific publications, and dozens of articles for lay and professional journals.  He blogs on Facebook at David Ramey, DVM and doctorramey.com.

Lara S. Worden, MSc.

Lara L. Worden, MSc., is an agriculture extension agent with NC Cooperative Extension. She has 15 years experience working in the field of livestock and equine production and nutrition. Although Lara works predominantly with cattle, sheep and goat producers, she has a passion for equine nutrition and forage quality and spends her spare time trying to help fellow horse owners improve upon their basic equine nutrition knowledge.

Q1: What are the signs of iron overload in a horse?

Kellon:

The most easily observed signs are bleaching of the coat and red tips on dark manes.  Severe cases develop liver disease. High insulin levels in EMS (Equine Metabolic Syndrome) horses are often associated with iron overload.

Ramey:

Iron toxicosis is rarely reported in horses.  Prior to 2019, chronic excessive oral iron intake has not been reported to cause clinical symptoms in equids.  However, in 2019, a report came out from the Netherlands of 21 horses and 1 donkey that had been drinking excessive iron in their water.  These animals had liver problems and iron salts deposited in the skin (a condition called hemochromatosis).  The development of the disease was slow and the clinical signs were not specific for any particular condition.

There was also an experimental study in 2001 in which 6 ponies were given excessive iron over an 8 week period.  The researchers couldn’t find any evidence of harm.  Finally, in 1993, 3 horses with signs of iron toxicity were reported, with signs similar to the 22 animals from 2019.  However, there was no evidence of excessive dietary iron intake in those horses.

That said, that may not be what you’re talking about.  I’m assuming that you’re asking about the assertion that excessive iron is somehow related to insulin resistance.  The fact is, that this not a real concern for equine nutritionists or veterinarians. 

All of this iron-insulin resistance stuff appears to trace to a 2012 study.

 Apparently, iron overload disorder can be a problem in captive rhinoceros, and the digestive tract of the horse is similar (not the same) to that of the rhinoceros.  So, in that study, 16 Arabian horses were used as a model.  They were given oral sugar solution and corn (not your normal horse diet) and researchers tried to find a relationship between serum ferritin levels (a measure of iron) and serum insulin (the hormone that allow the horse’s body to use sugar (glucose) from carbohydrates in their food for energy, or to store it as fat). 

In that study, researchers had a hard time establishing a relationship. For example, in the male horses, there was no relationship at all.  The researchers concluded that, “A relationship between iron accumulation and insulin sensitivity may exist in horses,” but only in female horses.  They also admitted that the statistical power of the study was weak due to the low numbers, and, “These results should be interpreted with caution and additional studies to control for such factors as age and gender are warranted.”

But even that’s not the end of the story. It turns out that the results were mostly the result of one horse in the study, that was referred to as an “outlier” by the researchers themselves.  As a result, the researchers said that their study “does not prove a link between serum ferritin and insulin resistance.”

So, in some, iron toxicity is a real, but rarely reported condition.  When horses have been reported with iron toxicity, they have not also been reported to have insulin resistance.  On the other hand, in the one study that used the horse as a model for captive rhinoceros, the researchers themselves were unable to prove a link between iron and insulin resistance.

Worden:

Iron overload symptoms in horses are likely a combination of direct iron effects and induced secondary deficiencies of other minerals (i.e copper & zinc). Common symptoms include coat color changes, either bleaching, “hooked/split end” appearance and/or red ends on manes and tails, often hoof issues such as poor overall hoof horn quality, abscessing and even laminitic issues.

Q2: Are there any tests your horse can undergo to confirm excess iron?

Kellon:

The only definitive test is the iron panel of ferritin, transferrin and serum iron from Kansas State Comparative Hematology Laboratory. No other lab does equine ferritin; the most accurate test in all species.

Ramey:

Sure – serum ferritin

Worden:

The only way to accurately diagnose iron overload is to test serum iron ferritin levels, which is a measure of the body’s total iron content. As far as I know, there is only one lab in the U.S. that test iron ferritin levels – Kansas State University Veterinary Hematology Lab.

Q2a: How accurate are these tests?

Kellon:

Very, validated against spleen and liver iron levels.

Ramey:

They’re accurate, in that they measure serum iron at the time that the blood was drawn, but the results aren’t necessarily meaningful in and of themselves.

Worden:

A standard serum iron test is not accurate. It reflects iron in the diet but not how much is stored in the body.

Q2b: Would you recommend getting one? If so, what should we know before getting our horses tested?

Kellon:

If indicated by the horse’s condition.  There are special handling procedures on the lab’s web page.

Ramey:

No.  Before getting your horses tested, you should note that the iron overload-insulin resistance correlation is not a concern for equine nutritionists and veterinarians.  Rather, it appears either to be a misunderstanding of or an over-interpretation of a single study, which itself didn’t establish a relationship.

Worden:

Not unless you have a metabolically challenged horse and you have exhausted all other options, such as diet and prescription drug management with little to no success. Not sure I am qualified enough to answer the second question.

Q3: What about forage? Do you recommend testing your grass and/or hay?

Kellon:

Yes.

Ramey:

No.

Worden:

Much of the forages that we feed to horses are naturally high in iron. The National Research Council recommends a minimum of 40 to 50 ppm (mg/kg) of iron for the average sized horse in the feed (this would be an average of all feed provided on a daily basis). This recommendation is a minimum requirement, but not necessarily an optimal requirement. The optimal amount may be, and likely is, a bit higher.

The NRC also clarifies the upper safe limit for iron in the diet to be around 500 ppm. This upper safe limit is based on the amount eaten. So if we assume that the horse eats 10 kg (22 lb) of hay per day at 500 ppm, then the upper safe limit is 5000 mg of iron per day. To put this into perspective, if we use the average iron levels (343 ppm) in mostly mixed grass hays from the Equi-Analytical forage testing lab and we again assume that the horse eats 10 kg (22 lb) per day, then the horse is consuming 3430 mg of iron, which is higher than the NRC minimum requirements but under the NRC upper safe limit.

Q3a: Where can we get hay/grass tested?

Kellon:

Commercial forage laboratories or state labs.

Ramey:

Commercial feed labs.

Worden:

There are a number of forage testing labs throughout the U.S. that one can used for a basic nutrient analysis of hay and pasture grasses, but one that is commonly used among horse owners is Equi-Analytical in upstate New York.

Q3b: How accurate are these tests? Is there anything we should be aware of?

Kellon:

Accuracy is good if many bales are sampled. A hay probe should be used.

Ramey:

The tests are accurate.  You should be aware of the fact that they are largely pointless, at least insofar as establishing a diagnostic or treatment plan for insulin resistance in horses.

Worden:

In order to have an accurate forage test it is important to have a representative sample. The method of sampling varies with forage type. When sampling hay it is best to use a core hay sampler. Take 10 to 20 core samples from each hay lot, then mix and sub-sample for analysis. Small rectangular bales should be sampled by coring from the end. Large round bales should be sampled from the side through to the core (center) of the bale in order to get a good cross section of the rolled hay.

There are essentially two methods to test forage – near infrared reflectance spectroscopy (NIRS) vs. wet chemistry. In a nut shell, wet chemistry is a bit more accurate, particularly for minerals, and pricier, but just for a standard forage analysis, NIRS generally gets the job done.

Q4: What should we look for in forage and other feed content?

Kellon:

Both adequate mineral levels and correct balance. The National Research Council has set an upper safe limit for iron of 500 ppm.

Ramey:

Good quality – fresh, good smelling forage and good quality feeds (most commercial feeds meet quality standards).

Worden:

Test the forages and feedstuffs fed and balance the trace minerals (i.e. iron, copper, zinc & manganese).

Q4a: What is the ideal ratio of minerals? What is acceptable? 

Kellon:

Ca:P from 2:1 to 1.2:1. Higher levels increase risk of bladder stones and sludge. Ca:Mg approximately the same. Fe:Cu from 4:1 to 10:1, Cu:Zn:Mn 1:3:3 to 1:5:5.

Ca = calcium; P = Phosphorus; Mg = magnesium; Fe = iron; Cu = copper; Mn = manganese

Ramey:

I guess the question is, “Which minerals?”  That said, horses can tolerate a wide range of mineral availability.  This makes sense, actually – a horse, or any biological system, wouldn’t be able to survive if it’s requirements for anything were overly tight. 

Worden:

Not sure that there is a universally accepted ratio of iron (Fe):copper (Cu):zinc (Zn):manganese (Mn), but it seems to be widely accepted that the ratio be somewhere in the range of 4-10:1:3-5:3-5.

Q4b: Does this change according to the horse’s workload? Age? Gestation/lactation? Disease?

Kellon:

Yes, to all four.

Ramey:

Workload? Mineral requirements?  No.
Age? Younger horses tend to have higher requirements for most everything – including protein and calories.  That’s because they’re growing.
Gestation and/or lactation?  Those mostly require extra calories, especially during lactation or the last three months of gestation.  You can tell if they’re getting enough calories by their body condition (if they’re too skinny, for example).
Disease? Well, that’s a pretty broad question – there are a lot of diseases – but in general, disease doesn’t affect nutritional requirements much.  Of course, there are disease conditions associated with some nutritional problems:  obesity and laminitis, for example.

Worden:

Workload, age, gestation/lactation: Iron requirements can and do change with workload, age and stage of production, but not by a lot. See the NRC Nutrient Requirements of the Horse Working Doc.
Disease? I am probably not qualified to answer this question, but with that being said, one needs to be careful of diagnosing a horse as anemic with just a standard bloods test. True anemia in horses is almost unheard of. Horses are really good at storing away red blood cells in their spleen and thus they won’t show up on a standard CBC test. Excess iron is a much more common occurence.

Q5: How should we compensate for excess iron content in forage?

Kellon:

Keeping Fe:Cu no higher than 4:1 and look for hidden sources of iron like water and supplements. Extreme cases may have body iron levels lowered by venisection (“bloodletting”) since red blood cells have a high iron content.

Ramey:

Well, honestly, I wouldn’t worry about it much.  The forage is changing all of the time and a single sample may not reflect the horse’s diet.  But if there were excess iron, I’d change the forage rather than trying to compensate for it.  I’d keep in mind that excess iron over a long period of time causes liver disease, not insulin resistance.  Lastly, I’d keep in mind that the insulin resistance-iron thing doesn’t appear to be a real problem anyway.

Worden:

Balance iron (and manganese) to essential copper and zinc.

Q5a: Are there any ration balancers you recommend? 

Kellon:

Uckele has an extensive line of vitamin/mineral supplements with no added iron.

Ramey:

No.  In fact, the whole premise of a “ration balancer” is a bit of a stretch.  Horses don’t have to have a “balanced” diet every day any more than people do.  They can have more of some things on some days and more of others on other days.  “Balance” is – or at least it should be – a general concept, not a specific one.

Worden:

Just about every major feed company has a ration balancer and in general, the differences between them are minimal. So my response to this question is the one that best balances the primary forages fed and that is readily available to you.

Q6: Is there any feed you would recommend?

Kellon:

I prefer whole oats balanced with either alfalfa or well rinsed beet pulp for horses that need a concentrate.

Ramey:

Other than, “Good quality,” not really.  That’s one of the really interesting things about horses.  If you look  at how they are kept around the world, they tend to do really well on a wide variety of feeds.  For example, horses in the wild do just great eating lots of fairly poor quality feed all the time.  In northern Europe, straw can be part of the diet (potatoes can be, too).  Some horses eat fermented feed (silage).  In California they eat a lot of alfalfa and in the mountain west it’s mountain Timothy.  Coastal Bermuda hay is probably the most commonly fed hay, but good hay is made from pasture grasses, too. 

For a horse in light-moderate work?  Mostly, those horses may need extra calories, which can usually be supplied with a little more forage.

For a horse in hard work (endurance, other demanding performance)?  Calories are the issue here, too.  For these horses, extra forage may not be enough.  They may need feeds that are more calorie dense because they may not be able to eat enough hay to fill their calories needs.  In those situations, fats or grains may be added.

For growing horses?  Growing horses need a bit more of everything since they’re growing.  The requirements change as they grow, too, for example, protein requirements drop as they grow older.  You can’t make blanket statements about “growing” horses – you’d want to ask about requirements at particular ages (and there’s been a lot of research on such things).

For pasture puffs? Pasture puffs generally need less of everything, especially calories.  In fact, obesity is a much bigger problem in horses than are nutritional deficiencies.

Worden:

This may sound like a cop out, but the answer to what feed I would recommend depends on – the age, current BCS, stage of production, level of activity and what major brands of feed are readily available.

Q7: What about any feeds you would advise us to AVOID for certain horses/scenarios?

Kellon:

Avoid anything with iron in the ingredient list if you suspect iron is an issue. Calcium phosphates and pelleting also add iron.

Ramey:

Sure.  Horses shouldn’t be fed excessive amounts of grain under any circumstances.  They shouldn’t be allowed to have excessive access to lush pastures (grass founder).  Avoid poor quality feed, e.g., moldy hay.

Worden:

In terms of iron levels, not particularly. Of course, there are those that say that all fortified commercial feeds are bad because they have added iron, but I would argue that the majority of the iron in said feeds is intrinsic (i.e. naturally occurring) and they generally only add a small amount to balance the trace mineral profile of the feed. Unfortunately, they cannot balance the trace mineral profile of the ‘entire’ diet because the feed manufacturers have no idea how the primary forages fed will test. So all they can do is balance the feed in front of them.

Q8: Is there anything else you would like to say? 

Kellon:

Iron overload has not been well studied in horses and is therefore underappreciated. Many nutritionists and veterinarians are unaware of the correct way to test for it.

References:
https://academic.oup.com/jn/article-abstract/114/4/677/4755646
https://pubmed.ncbi.nlm.nih.gov/30269378/?from_term=horses+iron+overload&from_size=100&from_pos=1
http://europepmc.org/article/MED/32042647

Ramey:

I think that some horse owners tend to worry too much about their horse’s diets.  It’s as if they think their horse is walking on the edge of a nutritional cliff, ready to fall over the edge at any time.  In fact, if a horse looks good – that is, he’s at a good body weight (you can easily feel the ribs), and is acting lively and energetic (“healthy as a horse”) it’s extremely unlikely that there’s also some nutritional time bomb that’s waiting to explode.  Yes, nutrition is important, but “precision” is rarely that important.  Keeping a horse in good condition isn’t – or at least shouldn’t be – that hard.

Worden:

Check out the ‘Iron Overload’ document in the Files section of the Equine Wellness & Nutrition FB group.

Resources

Where the idea for this blog started: Equine Wellness and Nutrition Group on Facoebook
Equine Cushings and Insulin Resistance on Facebook
Dr. Ramey’s Concise Guide to Medications, Supplements and Herbs for the Horse
Dr. Kellon’s Equine Supplements & Nutraceuticals: A Guide to Peak Health and Performance
My list of some good horse resource sites.