Stallion Handlers Should Be Moms

Some mom skills come in really handy – like sensing when things are too quiet and having eyes in the back of your head.  In many ways stallions are like overgrown kids.

This is not to make light of interacting with stallions in any way. They are quick, powerful and no mere human is a match for a stallion in a flat out battle. However, the common perception of stallions as aggressive and inherently dangerous is not accurate.  They are also not sex crazed maniacs that will hurt a mare and kill foals.  Nothing could be further from the truth.  Mares are much more of a threat to the stallion than the other way around and stallions are normally very protective of foals.

Stallions mellow with advanced age to rather stately and dignified gentlemen but in their younger days can be challenging.  It starts early. Colts are more active and physical than fillies, tormenting their dams from an early age with their penchant for mounting.  Rearing and mock fighting with their pasture mates is also a favorite.  As they become sexually mature, feral males form bachelor bands where they peacefully coexist but with an obvious herd hierarchy that is established through posturing and threats much more often than any actual physical contact. The posing is part of their daily interchanges with herd mates.

This behavior carries over to human interactions with domesticated stallions. The dominance  behaviors almost become a form of play where the horse is constantly trying to sneak in a nip, invade your space or keep you from entering his.  Calling his bluff with a sharp word and tap is sufficient to “win” if you are operating from a position of strength – i.e. have adequate restraint on the horse if he is out of the stall or have yourself in a position of power and movement if you are in an enclosed area with the horse loose. These encounters won’t be a once and done phenomenon.

The stallion will continue to challenge you every day and several times a day.  As handler and horse get to know one another, these exchanges can be almost invisible to an observer as a subtle change in body language communicates both the posturing and the response.  Like a mom, an experienced stallion handler can read their minds and convey the don’t-you-even-think-it message with as little as a sideways glance. The horse appears to only be quietly behaved but let someone else try to work with the horse and he can seem to be a different animal, immediately “in your face”.  There is no malice in the behavior though; no intent to inflict harm.

I’m leaving a lot out here, most notably the ground work training of breaking, leading, respecting your space, teaching the absolute zero tolerance for serious behaviors like rearing, striking and aggressive biting and making sure the animal has sufficient exercise and social interaction, with other horses at least visible. However, stallions are trainable just like mares and geldings.  On the whole, dangerous stallions are made not born.  They are a product of poor management and abysmal horsemanship coupled with excessive physical force.

It’s unfortunate that many horsepeople will go their whole lives without ever getting to know a stallion. They are a challenge and keep you on your toes but their unique zest for life is the essence of horse.

Eleanor Kellon, VMD

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Summer Allergies

Nothing ruins enjoying the warm weather with your horse quite like the scourge of allergies.  Manifestations run the gamut from sneezing and snorting to wheezing, runny eyes and agonizing itching.

from Towcester Vets, UK

Allergies are basically a misdirected and unbalanced immune reaction. When the immune system is exposed to a protein that is not a normal component of the body the usual response is to engage both major arms of the immune system (termed Th1 and Th2) to develop antibodies of the IgG and IgA class.  In individuals prone to allergic reactions, IgE antibody is produced and primarily the Th2 type reactions are activated.  When the sensitized immune system is next exposed to the same protein (called an allergen), a reaction is triggered which results in release of chemicals like histamine.

Why some horses are prone to allergy is not entirely clear but studies have suggested a strong  genetic component.  A horse can inherit the predisposition to develop allergies but will not inherit any specific allergy such as to a particular food.

Management of the allergic horse includes minimizing exposure to the trigger as much as possible. Antihistamines may be used to try to prevent the development of new reactions but antihistamines cannot reverse symptoms already present. Corticosteroids are typically prescribed for problems that do not resolve on their own.  They are extremely effective but come with side effects such as reduced immunity and metabolic disorder with chronic use or high dosages.

We can help the horse by providing supplements that support a balanced immune response.  At the most basic level this includes key antioxidant nutrients of copper, zinc, selenium, vitamin E and omega-3 fatty acids.  These are indispensable building blocks for the body’s own antioxidant defenses such as glutathione, EPA, DHA and the superoxide dismutase enzymes.

Vitamin C is a key antioxidant both in its own right and by virtue of its ability to regenerate other antioxidants, like vitamin E, to an active form.  It is abundant in fresh grass but activity is lost rapidly in hays. Vitamin C is particularly important in the respiratory system and the eyes.  Flavonoids (e.g. quercetin) are plant compounds which work synergistically with vitamin C. MSM also has documented antioxidant activity.

Spirulina is an edible algae which promotes normal balance between the arms of the immune system including supporting the production of IgG and IgA antibodies and healthy levels of histamine.

Finally, several herbs have been found to support a normal balance between the Th1 and Th2 arms of the immune system.  These include Astragalus, Siberian Ginseng (Eleutherococcus), Pau D’Arco and Echinacea.  Herbals used topically can also provide soothing relief for temporary irritations.  Ingredients that excel in this include Aloe Vera, Chamomile, Calendula and Chickweed.

There is no question that allergies can ruin your warm weather fun and torture your horse but there are several nutritional and herbal approaches that can be used to support normal function of the immune system and provide temporary relief for skin involvement.

Eleanor Kellon,  VMD

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Electrolyte Supplements

If you are thinking ahead to the imminent summer heat by looking at electrolyte supplements, good for you.  Horses lose massive amounts of electrolytes (and water) in sweat, putting them at high risk for dehydration, impaired performance, heat stroke, GI issues and impaired organ function.

An electrolyte is simply a mineral present in the blood in a charged electrical state, positive or negative.  The major electrolytes of nutritional importance are sodium, potassium and chloride.  In addition to the sweat losses with exercise, requirements also include sweat losses at rest in the heat and baseline losses in urine and manure (digestive tract secretions).

Sodium is most problematic because dietary levels are usually very low. In hot weather the baseline requirement is at least 20 g/day for a 500 kg horse which is equivalent to approximately 2 oz of salt.  Salt, sodium chloride, is the best choice for a sodium supplement since chloride level in the diet is highly variable and could also be low.  Levels in grass hay range from a low of 0.169% to 1.035% in the Dairy One database which contains over 40,000 samples.

After meeting the baseline requirements you need to compensate for sweat losses. Sweat contains approximately twice as much chloride as sodium and twice as much sodium as potassium. Your first step in selecting a supplement is to find one that approximates these electrolyte ratios although if your horse is not exercised heavily in the heat you can allow lower levels of potassium since the equine diet always has excess potassium. In other words, sodium can be greater than 2X potassium.  The relative electrolyte amounts in horses is very different from human sweat so using human products like powdered Gatorade is not advisable.

If the product label only lists salt rather than sodium and chloride separately you can calculate the amounts using figures of 40% sodium in salt and 60% chloride in salt. For example, if the % salt is 50%, sodium would be 0.4 x 50% = 20% and chloride 0.6 x 50% = 30%.

Once you have found a product with the correct ratios of sodium, potassium and chloride the next step is to figure out how much you would have to feed.  Product labels don’t always make this easy!  Law requires they always be listed as a %.  A product that is 10% potassium will provide 0.1 x 28.4 (28.4 g/oz) = 2.85 g of potassium per oz. You will need to know the weight of the serving size in grams (g) if it is different from 1 oz.  A half ounce serving would be 14.2 g (28.4/2) and at 10% potassium would provide 0.1 x 14.2 = 1.42 g of potassium.

A horse that is sweating only lightly will lose about 5 grams of potassium an hour  but if sweating heavily loses over 20 g/hour.  There is a HUGE variation in the levels of electrolytes provided in a  manufacturer’s recommended “dose”.  For example, potassium ranges from less than 1 g to over 9 g/serving so you have to do your homework and compare your horse’s actual needs to what each serving of the various products provides.

To summarize correct electrolyte supplementation:

  • Meet baseline sodium and chloride requirements first, using 2 oz of salt per 500 kg of body weight
  • Look for a product that provides approximately twice as much chloride as sodium and at least twice as much sodium as potassium
  • Once you have a supplement with the correct proportions of electrolyte ingredients, calculate how many servings you need using the guideline of 5 g of potassium for every hour of light sweating up to 20 g/hour with profuse sweating (500 kg horse).  Note: Because you made sure the proportions were correct first you only need to calculate servings for one of the electrolytes.  The others will follow along in correct amounts because the ratios are right.

Eleanor Kellon, VMD

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No Quick Fix for Laminitis Risk

It’s perfectly natural to want a silver bullet that will instantly remove the threat of devastating health problems like laminitis but it’s just not that simple.

         The classical laminitis stance is something you never want to see.

The latest proposed silver bullet currently popping up in mail boxes and on groups is a magazine article from 2016 regarding a vaccine developed in Canada.  The headline was “Laminitis Vaccine Offers Horse Owners a Preventive Tool”.

The vaccine is against two exotoxins produced by Streptococcal bacteria which proliferate in the hind gut when there is an overload of grain starch or fructan. These exotoxins are believed to trigger the enzymatic cascade that breaks down the laminar connections in hind gut associated laminitis.  In an experimental model the vaccine prevented laminitis in 20 out of 24 horses and reduced the severity in the remaining 4 animals.  Formal testing for regulatory approval has not been done.

Sounds really promising so far but there’s one big problem.  The vast majority of laminitis cases are caused by insulin resistance, not hind gut carbohydrate overload.  Streptoccal overgrowth and exotoxin absorption are not involved so obviously protecting against those exotoxins isn’t going to work.

There is no guaranteed protection against pasture laminitis with an IR horse. There are times of the day, weather conditions and grass growth stages that are more likely to be safe than others but no guarantees because grass is a living tissue with sugar and starch levels in constant flux.

Well controlled IR horses are more likely to escape without problems if they accidentally get pasture access, or if you roll the dice and allow grazing when sugar and starch levels should be safe.

Good control requires hormonal normalization if the horse has Cushing’s disease/PPID (pergolide) and an IR appropriate diet with sugar and starch intake at less than 10% of the analyzed nutrients.  Correct mineral amounts and balancing are also very important.  Common deficiencies and imbalances which are involved with normal functioning and hormonal activity include magnesium, phosphorus, copper, zinc, selenium and iodine.  If your hay was grown on alkaline soils, common in the mid West, adding chromium can be of benefit since uptake of this mineral is impaired in alkaline soil.

Acetyl-l-carnitine is a metabolite normally present in the body that supports insulin sensitivity in other species when supplemented.  Jiaogulan is a Chinese herb that also participates in insulin responsiveness and supports normal blood flow to the foot in the face of the high vascular tone induced by IR.

It’s not as easy as a shot in the neck but correct nutritional support for an IR horse is your best defense against laminitis.

Eleanor Kellon, VMD

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Myth Busting

It’s easy for opinions or hypotheses that are repeated often enough to eventually morph into what passes as a fact and from there to a myth that’s difficult to eradicate. These are three commonly repeated, but wrong, horse feeding myths.

Constant access to hay buffers stomach acid/Feeding grain increases stomach acid.  Damkel et al in a 2015 study fed horses either free choice hay, limited hay plus grain or the hay and grain diet with a pectin and lecithin supplement (75 g/100 kg of body weight). The horses had electrodes implanted in their stomachs to monitor pH.  Diets were fed for 14 days before starting the experiment.  Horses on the free choice hay had significantly lower (more acidic) pH values with a median pH of 2.69 over 24 hours compared to the the hay/grain diet (3.35) or the hay/grain diet with the supplement (3.4).  Similarly, Nadeau et al 2000 found much lower pH in horses fed a grass hay diet than in those receiving corn and alfalfa. As a corollary myth, it has also been widely stated that alfalfa will reduce ulcers and buffer stomach acid but Vondran et al 2016 fed grass hay, alfalfa pellets or alfalfa chaff to weanlings and found no difference in ulceration in most areas but greatly increased ulceration at the pylorus in the weanlings fed alfalfa chaff.

Depriving horses of 24 hour access to hay causes cortisol to rise from the extreme stress.  Gordon et al 2009 fed overweight horses a diet of either a high calorie pellet or reduced calorie, low carbohydrate weight control feed with 1% of their body weight in hay.  Hay was only fed once a day, in the afternoon. Grains were fed twice a day.  Some of the horses on weight control and restricted hay were also exercised.  The unexercised weight control horses lost significant weight and also had a large drop in their cortisol levels from 11 ng/mL down to 1.8 ng/mL.  Exercised also dropped from about 10.6 to 6 ng/mL (note: exercise increases cortisol naturally). The control horses that did not lose weight because of the high calorie grain had no significant change in cortisol with this feeding pattern (although it dropped a little in them as well.)  Two other studies also found a drop in cortisol when feeding was restricted.

Feeding high glycemic index diets (i.e. grain) causes insulin resistance.  Suagee et al 2013 fed nonobese horses feeds of 10%, 20% or 60% non-structural carbohydrate (primarily starch) for 90 days.  They found no change in insulin sensitivity with the high carbohydrate diet. This study was important because other work looking at the effect of diet was done with horses that were obese or were deliberately overfed and became obese. Bamford et al 2016 also showed that feeding 1.5 g/kg body weight of glucose every day for 20 weeks did not alter insulin sensitivity even though it caused the horses to gain weight. In fact, feeding glucose actually improved insulin sensitivity in these non-IR horses.

Even if it seems to make sense it is always good to question what you think you know – and what other people think they know too.

Eleanor Kellon, VMD


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Can We Prevent Arthritis?

Oral joint supplements/nutraceuticals have been with us for a quarter of a century. It didn’t take long after their appearance for the question to be raised regarding the potential to actually prevent arthritis.

                      Few active horses escape the bane of arthritis.

There are now hundreds of studies looking at the ability of oral supplements to prevent the development of arthritis or slow its progression. For example, positive results have been found for Boswellia in mice (Wang et al 2014), mussel extract in rats (Chakraborty et al 2010),  quercetin in rats (Gardi et al 2015), glucosamine in rats (Aghazadek et al 2014), glucosamine in overweight women (Runhaar et al 2016) and long term chondroitin sulfate in humans (Kahan et al 2009) just to list a few.

The situation in horses is a bit more complicated.  Being natural athletes they often make whatever they are doing look easy but the sheer size of the horse means tremendous forces are generated on his joints.  These are further magnified by obesity, work on uneven ground, pre-existing OCD or traumatic damage, any hoof imbalances, conformation imperfections, rider weight, rider errors and quite possibly genetics.  Preventing arthritis will never be as simple as giving a supplement. Nevertheless, there is reason to think we can have a significant effect.

In one of the earliest equine studies, White et al 1994, it was found that a commercially available chondroitin and glucosamine supplement did not protect against arthritis induced chemically by injection into a joint.  However, Vidella and Guerreo 1998 did find significant protection by both oral and injected chondroitin sulfate in a similarly induced condition.  The only difference between injected and oral was the injected chondroitin worked faster.

A small unpublished study by Dr. Smith at Rood & Riddle in Kentucky looking at Thoroughbreds in training with and without supplementation with hyaluronic acid oral gel for 59 days found statistically significant decrease in the number of horses evaluated for lameness when supplemented. HA greatly reduced postoperative joint swelling following surgery for OCD lesions in the hock, Bergin et al 2006.  Prevention of postoperative joint degeneration was also confirmed by a study looking at supplementation with ASU (avocado soy unsaponifiables) in a situation where damage was created surgically, Kawcak et al 2007.  They found no effect on pain but greatly improved cartilage quality.

In the most recent study, Leatherwood et al 2016 treated young Thoroughbreds with 30 mg/kg/day of glucosamine sulfate for 84 days before injected a carpal (knee) joint with lipopolysaccharide, a bacterial product which induces inflammation.  A matched control group was not supplemented.  The glucosamine group showed reduced markers of inflammation and cartilage breakdown, increased marker of regeneration compared to the injected control group. That dosage produced a blood level of glucosamine very similar to what was reported to be preventative in laboratory animals.

What to use at what dosage is the million dollar question. Firm answers just don’t exist but the evidence points to keeping at the high end dosages for at least one of the three major joint ingredients – 10,000 to 15,000 mg glucosamine, 2500 to 3500 mg chondroitin, 100 to 200 mg hyaluronic acid.

That’s what I’ve been doing with our racing Standardbreds for the last quarter century, starting when they are broken.  The difference in the incidence and severity of joint problems compared to the days before these supplements were available is undeniable. I’ve been around long enough to see both first hand!

Eleanor Kellon, VMD

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Do Horses Have Food Allergies?

Your immediate response would probably be – Sure, why not? That may well be true but you could be surprised to find out that a true food allergy has never been formally proven in a horse.

Seeds, nuts and grains are among the most common food allergies in other    species

A food allergy is defined as an unpleasant or dangerous reaction to the ingestion of a food. It can range from life-threatening immediate anaphylactic reactions to hives or swelling and tingling in the mouth or lips.  People may develop eczema and dogs often have itchy and inflamed ears, faces and/or paws.

Gastrointestinal symptoms may also be involved, such as abdominal pain, bloating/gas, vomiting or diarrhea although these may be symptoms of food intolerances rather than true allergy. For example, horses may be particularly susceptible to food intolerances because of the extensive fermentation in their hind gut.  The microflora of each horse is unique so the way they handle fermenting things may be different.

For all the horses you hear about  that are supposed to have feed allergies you would think that someone would have published on the problem by now.  A major difficulty is diagnosis. In humans and dogs it is well established that skin testing by scratch, patch or intradermal testing has at best 60% accuracy while blood testing for IgE levels is even worse. You might as well go through the list of possible allergens flipping a coin.

Despite this, blood testing for equine feed allergy is widespread and of course the companies claim it is useful. Are horses really different?  A 2016 study (DuPont et al) used a commercial testing service to do blood IgE allergy testing on 17 healthy ponies and tests were repeated twice to look at consistency of results.  They found 10 of the 17 tested positive for one or more food allergy but only 3 tested positive twice and only 1 tested positive twice for the same allergy.

Ponies with positive IgE tests were further tested with the “gold standard”, a challenge test where they were fed the identified offending food for 14 days and serum amyloid A levels were also monitored. Serum amyloid A is a very sensitive marker of inflammation.  There were no abnormalities in blood work or symptoms during the provocative trial.

Two studies have reported that intradermal testing can sometimes provoke signs of enteritis (intestinal inflammation) and hives in horses with food allergy confirmed by alleviation of signs when the food is removed from the diet.

A 2001 study (Lorch et al) looked at horses with known skin or lung allergic disease and compared reactions on intradermal testing to 3 different blood allergy assays. They concluded “None of the 3 serum allergy tests reliably detected allergen hypersensitivity compared with the intradermal testing”.  Morgan et al 2007 also confirmed IgE testing was not worthwhile for skin allergies and Tahon et al 2009 found the same for RAO/”heaves”.

If only by chance, the blood IgE tests are bound to get it right sometimes but research really does not support their use as a diagnostic tool.  Too many people are unaware of this and agonizing unnecessarily over what to feed their horse based on a host of positives on IgE testing.

The horse cannot be allergic to a food he has never been exposed to so if you see positives for things you never fed you can write that off.  Also realize that when showing the signs you suspect are a food allergy it has to be something he is eating then.  The best way to get to the bottom of it is list hay/grass type(s) and food ingredients for all feeds and supplements. Start the horse on a hay only diet of a hay type he has never eaten before. If symptoms resolve, start adding back individual foods (e.g. oats only) one at a time allowing 2 weeks between additions.  If you add an item the horse is allergic to or does not digest well, symptoms will return.

Eleanor Kellon, VMD

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Understanding Fat and Fatty Acids

Fat is much more than a storage form of calories.  The membrane of all cells contains fat. Fatty substances form a waterproof barrier in skin and hooves.  Some classes of hormone are derived from fat/cholesterol.  Some fats help regulate the immune system.

Fats from your horses diet are digested and absorbed as fatty acids. Once inside the horse they are stored and transported as triglycerides which are three (tri) fatty acids attached to a backbone of glycerol.

Sn = stereospecific numbering and refers to the fatty acid’s location on the glycerol.

There are five major naming systems for fatty acids.  In one seen commonly, fatty acids are referred to by the number of carbons in their chain, the “c” designation, as well as how many double bonds they have, e.g. C18:3 = alpha-linolenic, a dietary plant source of omega-3.

A horse’s natural pasture diet is low in fat with about 4% on a dry matter basis (food consumed minus its water content is dry matter). Hay is much lower at 2% because the fragile omega-3 fats in grass are lost with curing. Most horses benefit from some fat supplementation when not on pasture.

No research has been done on dietary fat requirements of horses. The horse can manufacture all the fat it needs for vital functions but skin, coat and hoof quality may decline on low fat diets. The only fats considered a dietary necessity for any species are the essential fatty acids, omega-3 alpha-linolenic and omega-6 linoleic.  Again, there is no equine research but if we use the evolutionary diet, grass, as a guide the horse should optimally get a ratio of omega-3:omega-6 of about 4:1.

All grains and most readily available vegetable and seed oils are higher in omega-6  than -3.  The only choices with high omega-3:omega-6 ratio are flax or chia.  Chia and flax seed are typically supplemented at a rate of between 2 and 16 oz/day.  If using a liquid oil give approximately 25 to 30% of this amount.

The omega-3:omega-6 ratio is believed to be important because in other species it influences the balance between inflammatory and antiinflammatory cytokines in immune responses.  This makes it very difficult to avoid omega-6 overload in horses that need added fat for weight or control of EPSM.  There is now an option.

I avoid talking about specific products for the most part but this one is unique. Uckele has a new fat source called CocoSun, available in liquid or powder.  This combines extra virgin coconut oil with extra virgin, organic sunflower oil from a special strain high in  omega-9 (oleic acid).  Oleic acid is also the major fatty acid in olive oil.

You can feed this with flax without upsetting the omega-3:6 ratio.  Coconut oil is rich in medium chain triglycerides which the body prefers to burn rather than turn into fat stores and the monounsaturated oleic acid has metabolic benefits in other species.

Feeding fat optimally takes more thought than just grabbing some oil off a store shelf but armed with the facts you can maximize the benefits you get from adding fats to the diet.

Eleanor Kellon, VMD

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Transitioning onto Pasture

Spring grass is mother nature’s panacea for winter’s nutritional hardships and the huge demands of pregnancy and lactation.  However, rangelands utilized by feral horses usually bear little resemblance to the fields of domesticated horses and even in the spring their diets also include high fiber items like shrubs. Unlimited access to powerhouse grasses can cause some problems.

Young grasses are low fiber, very high protein and higher in rapidly fermentable carbohydrate fractions than more mature growths.  This can lead to a variety of hind gut digestive upsets including bloating, varying degrees of manure softening/diarrhea and in some cases colic.  This can be avoided by careful introduction to the new grass.

Given the option, every horse will gorge on the succulent young grasses and largely ignore anything else you try to get them to eat – including grains in many cases!  When their large intestine is packed full of the rapidly fermenting grasses it produces conditions that do not favor proliferation of fiber fermenting organisms.  To balance this out, keep the horses off the grass for 12 to 18 hours per day with access to good hay. When the pasture is particularly dense it may need to be longer than this.  Gradually allow longer grazing periods always keeping a close eye on manure.

Supplementing with live yeast cultures is also beneficial. Yeast have been documented to help avoid the large changes in the colonic environment that have a negative impact on fiber fermentation.  It is also useful to feed a source of easily fermented soluble fiber to further support the fiber fermenting organisms.  Psyllium and beet pulp are particularly good sources.

Spring grasses can also be low in magnesium and sometimes other major minerals such as calcium as well.  Sodium levels are typically quite low.  Combinations of these factors may interfere with digestion or intestinal motility and can even result in electrolyte disruptions such as thumps.  Magnesium sensitive horses can also show increased nervousness and muscular twitching. EPSM horses often have noticeable increase in symptoms which could be from low magnesium intake and/or high sugar and starch in the grass.

Speaking of sugar and starch levels, insulin resistant horses are at extremely high risk of developing laminitis. It may not be a full blown laminitis every year but there will always be damage to some degree. There is no way to prevent this, no supplement or management approach that makes spring pastures safe for IR horses.

If reaction to low magnesium is suspected, supplement with 5 to 10 grams/day.  All horses should also receive a minimum of 1 oz of table salt/day in their feed.  If  free choicing salt, use a coarse granular rather than salt blocks, fed in a covered feeder.  Daily formal exercise is particularly important for EPSM horses on lush spring pastures. If worsening symptoms persist, pull them off pasture until it has matured.

There can definitely be too much of a good thing with high quality spring pastures. Controlled intake and a few intelligently selected supplements will help your horse get maximum benefit without the drawbacks.

Eleanor Kellon, VMD

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The Genetics of Insulin Resistance

Insulin resistance [IR], which is a failure of insulin responsive cells to take up glucose under normal levels of circulating insulin, affects an estimated 12 to 15% of horses. Insulin resistance is typically (but not always) associated with easy weight gain.  Abnormal fat deposits are usually evident. The most important consequence, however, is a risk of developing laminitis.

In a well-intentioned effort to protect horses from laminitis caused by uncontrolled IR, many things have been proposed as causing IR.  These include feeding grain, improved strains of pasture grasses, insufficient exercise, obesity and a host of proposed environmental factors including pesticide and herbicide exposure.

Arguing against the idea there are external causes is the observation that there are very clear breed risk factors for IR, with it being extremely rare to nonexistent in some, like Thoroughbreds, but very common in others, such as Arabians.  Furthermore, the Virginia Polytechnic large long term study of IR in a herd of mixed breed ponies also found strong evidence of a genetic component when they did pedigree analysis.

Most recently, a study just released in the Journal of Animal Science searched the genome of the Arabian horse and identified a genetic risk locus where markers correlated with laminitis, high blood insulin, abnormal indirect measures of glucose metabolism and potential obesity.  The findings were strong and confirm that IR has a genetic cause.

It is also true that feeding an inappropriate diet, no exercise and letting the horse get obese will indeed worsen IR.  So, if these are factors that need to be watched closely what difference does it make whether they actually cause it or not?  It makes a big difference.

If someone has a life-threatening strawberry or peanut allergy, they must avoid those things at all costs but can otherwise live a perfectly normal life if they accept and respect that restriction. The allergy does not go away, it simply is managed by avoiding the dangerous trigger. The same is true for an insulin resistant horse.

On the individual level, if a horse diagnosed as insulin resistant is put on an appropriate diet, exercised and loses weight, eventually resulting in blood insulin levels returning to a normal range, that horse is not cured of insulin resistance.  The underlying genetics are still there.  Failure to appreciate that leads people to do things like turn the horse out on unsafe pastures that put them at risk of deteriorating and developing laminitis.

Buying into the idea that IR can be caused by diet has also led to an epidemic of concerned owners becoming positively paranoid about feeding any starch and the simple carbohydrate levels in pastures. While it is certainly true that many horses do not need supplemental grain (or fat calories), it is not a metabolic poison that must always be avoided. Similarly, the vast majority of horses are not at risk of laminitis from pasture levels of simple carbohydrates.  Despite this, grass “sugar” tends to be blamed for a host of hoof quality issues, hoof tenderness and even thrush when the real cause(s) has nothing to do with sugar.

It is important to be diligent about correctly identifying and managing horses with IR as early as possible for the best outcomes.  It is equally important to realize this is a lifetime commitment.  At the same time, remember that the vast majority of horses do not have this issue and there is no reason to be unduly restrictive with their turnout or diet and certainly no need to buy into a long list of supplements to treat or prevent a condition they do not have.

Eleanor Kellon, VMD

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