Cold-Induced Laminitis

It happens every winter. A horse that may not even have a prior history of laminitis is found to be very lame and reluctant to move.  It’s more than the typical hesitation horses show on hard, frozen ground. Looks like laminitis but the feet aren’t hot. What’s going on?

Cold-induced hoof pain strikes horses with insulin resistance. IR is a well described risk factor for laminitis and even when the horse is not glaringly lame it is causing damage to the laminae. We haven’t uncovered all the mechanisms behind laminar damage from high insulin levels but one known factor is elevated levels of endothelin-1.

Endothelin-1 is a peptide (small protein) produced by the cells lining the interior of blood vessels. It is the most potent vasoconstrictor known and is normally balanced by production of the vasodilating chemical nitric oxide. Cold-induced reduction in blood supply to the hoof when superimposed on the pre-existing high endothelin-1 activity may explain why some IR horses develop hoof pain in cold weather but normal horses do not.

Cold stress may also cause insulin to rise.  Insulin resistance is part of the metabolic adaptation to cold weather in several species.  Researchers have also noted insulin levels become erratic in horses in cooler weather.

Laminitis caused by high insulin is different from laminitis due to other causes.  Activation of enzymes and inflammatory reactions are not part of the picture.  This probably explains why the usual treatment with NSAIDs [nonsteroidal antiinflammatory drugs] like phenylbutazone has little effect.  There is help though.

Blanketing the horse when temperatures dip below the equine thermoneutral temperature of 45 F helps avoid cold stress. Keeping the lower legs wrapped and feet protected inside lined boots also helps maintain normal circulation to the distal extremities.

Adaptogens are herbs which support a healthy response to stressors like cold weather. Jiaogulan [Gynostemma pentaphyllum] is a particularly good choice because this herb is also known to support production of the vasodilator, nitric oxide. Jiaogulan should be given twice daily, preferably before a meal. Most horses love the taste and will lick it up as a powder or paste.

L-arginine is the amino acid precursor for nitric oxide and can be supplemented along with the Jiaogulan. L-citrulline is another amino acid that the body converts to L-arginine for nitric oxide production.  Cold stress also results in considerable oxidative stress and antioxidants help neutralize these free radicals.

Finally, acetyl-l-carnitine supplementation can be indicated for support of normal nerve function and glucose handling.

When you understand the trigger of winter laminitis you can support the horse with simple measures to minimize cold stress and maintain normal blood flow to the feet.

Eleanor Kellon, VMD

 

 

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Pica

Pica is defined as ingestion of items with no food value over a period of at least one month. This is actually normal in the young of all species. Horses rarely fit the description of chronic consumption except for devoted wood chewers but sporadic eating of dirt or manure is fairly common.

Bark stripping yields negligible nutritional benefits and could be considered a form of pica.

Most formal research has been done in humans and may not be directly relevant to the horse but at least they can provide feedback.  Pica is seen in a number of developmental or psychiatric disorders. It is also commonly associated with anxiety, which may fit well with the equine picture.

In people, an association has been noted between pica and pregnancy and/or anemia. However, this has been difficult to tease out from other associated factors.  For example, dirt eating during pregnancy is a cultural practice in some developing countries where dirt is actually sold by street vendors.

Detailed analysis of many studies has been unable to settle the chicken or egg question regarding a connection between mineral deficiencies and pica. One problem is that dirt eating often focuses on clay (same is true of animals) and clay can bind nutritionally beneficial minerals and/or be a source of toxic ones like lead or aluminum.

Another interesting association with pica reported by humans that we really can’t confirm or rule out in animals is that it can be caused by nausea.  Clay is the obvious choice for relief of any GI upset and is a common ingredient in both human and animal products for both gastric upset and issues with diarrhea and gut toxins.  Clay binds many fungal and bacterial toxins and is a major ingredient in Kaopectate.  Horses are certainly no strangers to GI upset in many forms.

Eating feces (coprophagia) should be in a special category because it does have some nutritional value. It is so common in rats and rabbits that the practice is considered a normal behavior used to obtain protein and minerals that are not well absorbed from the large bowel and would otherwise be wasted. In fact, deficiencies can develop is they are prevented from eating feces. It is also a perfect prebiotic that is not only rich in live organisms but also precisely the types the animal needs.

Coprophagia is also normal in foals, piglets and even young ruminants like calves and sheep.  Dogs are notorious for eating the fecal matter/manure of a variety of other species.  Cats will eat their own feces out of hunger or boredom (reduces or stops if they are allowed free choice access to food) or when vomiting. It’s unclear if they are eating feces to induce vomiting (e.g. hairballs) or to attempt to recover nutrients.

So, what do we actually know about aberrant feeding behaviors in horses?  Two studies in horses from the late 1970s identified low protein intake as a trigger for coprophagia which fits with data from other species. No solid connection with mineral deficiencies has been documented although by observation dirt eating may increase in ill horses and could be an instinctive but nonspecific drive for minerals. Horses may also eat dirt or lick metal when seeking salt.  Pica as an outlet for anxiety, boredom or not having food available is likely an issue in many scenarios, as is dirt eating related to GI upset.

Fortunately, most of the possible causes are benign.  Small net hay feeders, toys, plenty of exercise and a quality diet may help prevent pica. However, if anything seems “off” when your horse starts odd eating behavior it’s best to involve your veterinarian.

Eleanor Kellon, VMD

 

 

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Cold Weather and Stiff Horses

Research has proven that exposure to cold causes increased stiffness in both muscle and connective tissue, including tendons and ligaments.  A recent human study also confirmed that dampness (relative humidity) is correlated with increased joint pain and this effect is worse when the weather is also cold.

The effects are magnified in older horses.  “Sarcopenia of aging” is age related loss of muscle mass which gets worse if the horse is not regularly exercised.  Age also causes increased tendon and ligament stiffness/loss of flexibility and lesions develop in the core of flexor tendons.  To top it all off, muscle is less strong in the cold because energy generation becomes less efficient, allowing more energy to escape into the cells as heat.

The end result of all this in its mildest form is horses which have a wooden, stiff movement. In the worst case scenario they are so severely affected that getting up from a down position becomes very difficult or even impossible.  Fortunately, this scenario isn’t inevitable.

All horses require an adequate place to shelter from precipitation and winds in the cold. For the horse prone to cold related stiffness, it’s critical. Blanketing to preserve body heat and support muscle energy generation and soft tissue flexibility is also desirable. For horses prone to stiffness, don’t wait until they are shivering.  If the hocks or knees are known to be an issue, look into Neoprene or lined boots to keep the joint warm when the horse is confined and/or overnight.

Wraps can also be used for the lower legs to protect those joints and the tendons and ligaments. Lined shipping boots with Velcro closures are often a good option because they cover from below the knee to coronary band, are very warm and can’t cause problems related to slipping and too much pressure.  Hoof boots with a liner between the bare rubber and the horse’s sole are also helpful.

Horses with obvious areas of discrete muscle/tendon/ligament involvement rather than a stiff all over picture can benefit from use of a topical containing capsaicin.  Mint in the formulation will increase the warming effect.

Supplements to support homeostatic defenses against cold-related oxidative stress can be very helpful. Look for ingredients like Devil’s Claw, Cat’s Claw, Turmeric, Boswellia and Yucca. On the nutrient end, good choices include MSM, berries, Resveratrol, Quercetin and Grape Seed Extract.

Finally, bolster normal joint cartilage maintenance with the big three of Glucosamine, Chondroitin and Hyaluronate plus connective tissue support in the form of Green-Lipped Mussel and hydrolyzed collagen.

Winter is a stress on any horse, even moreso for seniors. Supportive measures don’t have to be complicated if you understand the physiology and the tissues you need to target.

Eleanor Kellon, VMD

 

 

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Co-Products, not By-Products

There is a trend these days to label many highly nutritious feed ingredients as worthless wastes.  This particularly falls on anything that might be classified as a by-product, including beet pulp, wheat mids, soybean hulls and distiller’s dried grains.

Do you consider such things are semolina, wheat germ, rice bran, linseed meal, corn meal, couscous, molasses, copra (coconut meal), Psyllium, and bran cereals to be by-products? Probably not, but like the ingredients listed first they are all co-products generated during the processing of a food to remove certain portions of it.

        Psyllium products are made from the thin coat surrounding Psyllium seeds

Soybean meal, like all seed meals, is a co-product of the oil extraction industry. They have all of the protein, carbohydrates/fiber, vitamins and minerals of the original food, just not the high fat. As a plus, reducing the fat considerably boosts the protein percentage in the meal.

Some of the prejudice against co-products likely arises from unfamiliarity. You won’t find beet pulp on the shelf in human food stores because people can’t digest it – but horses can. Beet pulp is a low sugar, essentially zero starch, high soluble fiber that is easily fermented in the horse’s hind gut, is prebiotic and yields more calories/energy than hay. The same is true of soybean hulls.

Some co-products have unique characteristics. Feeding distillers’ or brewers’ dried grain instead of corn, etc. means starch and calories have been reduced to very low levels via fermentation of the grain but palatability is retained and protein is significantly higher than in the grain.

Psyllium (Plantago) husks are another specialty co-product. They are the thin outer coating on Psyllium seeds and are rich in mucilage, a form of soluble fiber.  When fed on an intermittent basis they are an effective way to enhance sand removal from the colon. When fed on a daily basis they become a prebiotic as the hind gut organisms adapt and begin to ferment them.  An added bonus is that wet Psyllium gives a distinctly slippery/slimy coating to a meal which makes it easy to swallow.

Co-products may be criticized because they are not whole foods but the whole foods mentality can be carried too far. Do you eat peanut shells or walnut hulls when you eat those foods?  Lemons, bananas or oranges with the peel? Of course not, because they are largely undigestible and/or unpalatable.

Co-products may actually have enhanced nutritional qualities for the horse. Beet pulp, distillers’ dried grains, brewers’ dried grains are safer because of greatly reduced sugar and starch levels.  Seed meals have reduced calories because of fat removal and higher % of protein. Brans and seed coats have very good to high protein levels, low sugar/starch and are good mineral sources. Wheat co-products have all the concentrated nutrition of wheat without the starch, which was processed out to make white flour for people.

Not all co-products are appropriate for horses (e.g. oat hulls or cottonseed products) but those you find in feeds and supplements typically are. Be fully informed before you make a judgement call.  There’s a good chance your own diet contains co-products.

Eleanor Kellon, VMD

 

 

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Air Quality in the Barn

When the winds are up and temperatures drop we want our horses to be comfortable and protected. Nestling into a cozy stable may seem like a good solution but there are health risks lurking in a tightly closed up barn.

Fine particulate matter and fungal elements from stored hay and straw are a major source of respiratory irritation in barns with poor ventilation.

Horses with respiratory issues actually breathe easier in cold, dry air.  However, this winter advantage is lost when horses are confined to a poorly ventilated barn where humidity and particulate matter in the air is high.

An elevated concentration of irritants in the air causes measurable lung inflammation in all horses. There may or may not be a true allergic component. Continued exposure can lead to IAD (inflammatory airway disease) or RAO (recurrent airway obstruction) in susceptible horses. These conditions have a considerable impact on the horse’s comfort and performance. There may be increased risk of infectious lung disease or irreversible damage in chronic cases.

A variety of airborne substances have been implicated. Ammonia from bacterial breakdown of urea in urine is a well documented lung irritant in a variety of species. “Organic dust” is also an offender. This includes microscopic particulate matter from mites, plant material (e.g. beta-glucans), feces, bacteria and their products (endotoxin) and fungal spores.

Keeping stalls clean and the building well ventilated are the first steps in reducing exposure. Using wood chips or synthetic bedding (e.g. paper based) reduces plant and fungal matter but must be used in all the stalls. Horses are also exposed when hay or straw are stored in the same building, even in a loft.  Horses with clinical signs should have their hay and bucket fed meals thoroughly wet down. Always strive to remove horses from the barn when stalls are being cleaned and aisles swept.

These measures will go a long way in reducing risk of developing lung disease and reducing breathing difficulty in horses that already have it but they cannot completely eliminate exposure and some horses will need more help.

Medical treatment includes a variety of systemic or inhaled agents including corticosteroids, bronchodilators and mucolytics.  There are also supplements you can use to assist the horse’s body in normal respiratory function and maintaining healthy tissues.

Exposure to lung irritants and activation of the immune system results in considerable oxidative stress. Vitamin C is an important antioxidant in the lung and studies have shown low levels of vitamin C in the lung fluid of diseased horses. Oral dosages of 4.5 to 10 grams/day are used for the average size horse. Antioxidant activity can be boosted by pairing it with sources of plant antioxidants such as Grape Seed and citrus bioflavonoids.

Nagging coughs are a common sign of both infectious and noninfectious lung disease. The coughing itself is also irritating. Human over the counter lozenges and chest rubs take advantage of the ability of aromatic oils like camphor, eucalyptus, menthol and orange to help maintain open, relaxed airways with thin mucus that is easily cleared. They work the same way in the horse and equine specific products are available. Pastes are easiest to administer.  Look for a soothing base with ingredients such as Aloe vera, apple cider vinegar, glycerin and honey.

Spirulina, 20 grams twice daily, helps the horse maintain lung homeostasis by stabilizing mast cells and supporting a balanced immune response.  Jioagulan supports control of stress responses and maintenance of relaxed bronchial tone. Omega-3 fatty acids from flax seed provide the raw materials for normal balancing of inflammatory reactions. MSM also assists the body in balancing its responses to triggers of lung irritation.

Controlling exposure to lung irritants greatly reduces your horse’s risk of developing chronic lung disorders.  If you do have to deal with signs of lung irritation there are many options, including nutritional support for normal lung function.

Eleanor Kellon, VMD

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Spirulina for Insulin Resistance?

First, I’m a huge fan of supplemental Spirulina platensis and have been for many years. There has been buzz this fall surrounding a study that supposedly shows Spirulina supplementation reversed Equine Metabolic Syndrome [EMS].

Spirulina platensis under the microscope.

The study by Nawrocka et al appeared in the August 2017 issue of the journal Marine Drugs. In the first part of the study the researchers quantified fatty acids, amino acids and other components in the Spirulina. They also confirmed its previously documented antioxidant benefits in cultured equine cells.

The second part of the study utilized three groups of horses – normal, EMS and EMS on a Spirulina supplemented diet.  After 3 months on the experimental diets 5 of 6 horses in the EMS + Spirulina group tested normal on a CGIT – combined glucose and insulin tolerance test. A popular equine lay magazine reporting on this study stated this indicates the horses were negative for EMS after 3 months but this is not accurate and also not what the study said.

The CGIT test is not reliable in horses.  It has poor sensitivity, which means there is the potential for many falsely negative/normal results.  It also has poor repeatability. Results from one test date can be very different from another in the same horse. The bottom line is that we can’t rely on those findings but it should be noted significant changes only occurred in the EMS horses supplemented with Spirulina.

Among the other changes noted after three months in the Spirulina group was weight loss. However, the horses were on a diet of 1.5% of the body weight in timothy hay which alone could explain the weight loss noted.  The EMS horses not given Spirulina did not have a weight loss but the article did not give details about the differences between the pelleted feeds the EMS horses in the two groups received. The EMS + Spirulina group also showed a reduction in the cresty neck score, but not to a normal level.

Four out of six of the EMS + Spirulina horses had a significant reduction in their insulin levels while the EMS group not on Spirulina did not. The insulin levels were still very abnormal, but lower. Again, it is unknown to what extent differences in the composition of the pelleted feeds given to the two EMS groups might have contributed.

Leptin, a marker of insulin resistance independent of insulin and glucose dynamics, was not changed by Spirulina supplementation.

The study did not give the actual dosage of Spirulina that was used, or whether the horses were monitored to see if they were actually consuming the whole dose. This is a significant point because Spirulina is not particularly palatable.  In my experience, when horses are presented with Spirulina pelleted into a palatable base and mixed into their usual meal 1/3 will refuse to eat it, 1/3 eat slowly and may not eat it all while another 1/3 will consume it readily.

This isn’t the first time Spirulina has been investigated in metabolic syndrome/insulin resistance. Benefits have been shown in humans and laboratory animals. However, there are significant differences in the syndrome between these species and the horse.

The take home message is there are many questions regarding this study. Even if the findings are reliable, it’s not a cure by any means.  Controlled calorie intake using a diet of low sugar + starch hays with small amounts of similarly low sugar + starch carrier feed for supplements, plus as much exercise as possible, remains the foundation of management of Equine Metabolic Syndrome.  For details based on over a decade of following thousands of these horses please visit http://www.ecirhorse.org.

Eleanor Kellon, VMD

 

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Hoof Health Fix in the Off Season

It’s tempting to let hoof care slide a bit when you’re not working your horse but if you do you will be missing a perfect opportunity to improve hoof health.

The back of a healthy hoof cushions the internal structures and absorbs shock like the heel of a well constructed athletic shoe.

It used to be standard procedure to pull a horse’s shoes for the off season, and with good reason.  The hoof may seem like a pretty rigid structure but when unshod there is measurable expansion at the quarters when the hoof is weight-bearing.  An unshod hoof also engages the frog as a natural shock absorber and integral part of the weight-bearing structures.

When a horse is shod, expansion on weight-bearing is restricted and the frog does not receive as much direct stimulation as when the horse is barefoot. As a result, the heels and frogs tend to narrow over time (contracted) and the foot takes on a more oval shape. Less shock absorption means more vibration is transmitted to the internal structures of the hoof and leg.

When the shoes are pulled it’s not unusual to be able to see the heel area expand within a matter of hours. By a few days, the feet are obviously wider. The frog responds to stimulation by becoming larger and more robust.

Another benefit of the natural expansion and contraction of the bare hoof is that material in the crevices beside the frog are forced out when the horse walks.  This reduces the risk of thrush.  The same pumping action keeps snow from accumulating in a bare hoof and unshod horses have better traction.

If the horse has been protected in shoes for a long time the hoof wall may be thinner than it would be otherwise. This will also respond to the stimulation of being barefoot. To prevent cracking and chipping the hoof ground edge is usually rounded to produce what is called a “mustang roll”. This should always be done if the hoof wall is of poor quality or the horse will be moving over hard surfaces.

The rolled or beveled hoof edge also relieves strain and tension on the laminar connections, leading to a tighter white line. As laminar connections improve, the coffin bone will sit higher within the hoof capsule and you will see good natural concavity developing in the sole.

Another advantage to being barefoot for a while is that the horse can move, break over and wear the hoof in the way that is most comfortable for them.  This can provide valuable information for the veterinarian and hoof care professional.

Whether barefoot or shod, it’s important to maintain an interval between trims that keeps the hoof from becoming overgrown and distorted.  Hoof wall distortions are a very common cause of lameness both in the hoof and the structures above. Even when they are not the direct cause, improper hoof mechanics caused by an overgrown hoof will have a negative impact.

The off season is the time for your horse to rest up and recuperate.  Pulling the shoes and regular hoof care during this period also makes it possible to return the horse to work with the best possible hoof health.

Eleanor Kellon, VMD

 

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The Skinny Older Horse

Impending winter weather and loss of good pasture make all owners of thin senior horses anxious.  Some things to consider when a horse is underweight span all age groups, but seniors have additional considerations.

CHEWING SURFACE

Transverse ridges on the chewing surface of molars and premolars are important for breaking down food but become worn smooth with age.

Older horses need frequent, but not necessarily aggressive, dental care. Problems such as worn teeth, loose or missing teeth, abscesses and gum irritation from food packing into diastemas (gaps at the gum level) are common older horse issues which interfere with effective chewing and/or cause pain. Wear also changes the angle of the chewing surface which reduces the effectiveness of chewing.

The goal of dentistry should be to remove pain, not necessarily “fix” things. Horses with significant dental issues reap the most benefit from a wet, if not soupy, diet. Hay cubes or pellets can be thoroughly soaked, as can complete feeds,  beet pulp and bran. Get professional advice in formulating the diet.

I commonly recommend incorporating psyllium into these wet senior diets. It further increases how easily they are swallowed (choke is a concern with seniors) and is an excellent prebiotic. Use 1 to 2 oz of psyllium husk fiber per meal.

Older horses often have reduced natural immunity to parasite infections and may even become positive for parasites normally only seen in foals, like roundworms. This is one cause of weight loss you can control. Keep an eye on fecal egg counts and work with your vet on developing an individual deworming program for your  senior.

Supplementing fat, up to 0.5 kg/day, considerably increases the caloric density of the diet. Begin with a flax based supplement to replace omega-3 fatty acids if the horse is not on fresh grass. Use at least 0.12 kg/day of this or even up to 0.5 kg/day.  If feeding less than the full 0.5 kg/day of flax based supplement I recommend making up the difference with something that will not upset the omega-3:omega-6 ratio, like Uckele’s CocoSun.

Senior citizens of all species may suffer from reduced  digestive efficiency. Even the diversity of the microflora in the large intestine of the horse decreases with age.  A supplement with both high digestive enzyme activity and good numbers of live probiotic organisms can be very helpful for seniors.

Vanishing toplines is a common complaint with older horses. When this is seen the horse should always be checked for PPID – pituitary pars intermedia dysfunction, aka Cushing’s Disease – because high cortisol activity in these horses causes muscle loss. There may also be a factor of poor protein digestibility and/or inadequate key amino acid intake.  Supplementation with the triple combination of L-lysine, D,L-methionine and L-threonine is an inexpensive safeguard on the nutritional end.

Problems such as heart failure, kidney failure, liver disease or malignancies are rare in younger horses but anything goes with a senior. All of these may have weight loss as a component. It’s always wise to involve your veterinarian when having weight issues with a senior.  Odds are one or more of the factors mentioned earlier will be the explanation but keeping your vet informed of the issue and what was tried will save precious time in deciding on diagnostics and treatment down the road.

Eleanor Kellon, VMD

 

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Impaction Season

Colic remains the #1 health issue of horses across all ages, sexes, breeds and uses. There are many forms of colic and impaction is one of the most common.

MANURE MUCUS

The stringy, sticky, white/tan coating on this manure is mucus, a red flag warning sign for impaction.

Several things have been identified as risk factors for colic, including reduced exercise, diet change and tapeworm infestations.  These factors converge in the fall and winter with a diet change from pasture being a double whammy because of the very low moisture content of hay compared to grass.  Tapeworms are picked up during grazing season so have reached peak numbers and size.  It doesn’t help matters that bot fly larvae attached to the stomach lining have also reached a large size and may cover a significant amount of the stomach’s surface.

Early signs are easy to miss. Manure is present initially but total volume is less.  Some manure may have a coating of mucus.  The horse also continues to eat but will gradually decrease amounts. There is depression but obvious signs of colic do not usually appear until the obstruction is complete or near complete.  The horse often continues to pass manure for a while even when blocked because any manure that was present past the impaction will continue to move out.

Pain severity varies but can be quite dramatic in some horses. However, the color of their mucus membranes/gums remains good.  Pulse is moderately elevated.  They usually respond well to analgesics such as flunixin meglumine (Banamine) but typically need twice daily dosing.  When pain reduces because of treatment they will often eat, but eating quickly causes more pain.

Treatment also involves fluids intravenously and/or by stomach tube.  Softeners, mineral oil and/or osmotic laxatives like magnesium sulfate are commonly used.  Most cases resolve without surgery in about 3 days, but it can take as long as a week for the blockage to clear.  Enemas are sometimes used as the blockage moves closer to the small colon and exiting.

The most important part of avoiding impaction is keeping the horse and his intestinal contents well hydrated.  The best way to do this is to guarantee adequate daily salt intake.  For an average size horse that is not exercising/sweating this is at least 1 oz (2 tablespoons) per day. Horses over 1100 lbs need more.  Add this directly to the bucket meals. If the horse won’t eat enough salt this way, dissolve it in water and spray on the hay.

There must also be a constant supply of water at a palatable temperature – often a tall order in cold weather.  They will drink the most during and after eating and if the water is around body temperature. If you don’t  have hot water in the barn, invest in a heating coil. Make watering the last chore and offer warmed water two or three times a day.

Make sure the horse spends as much time as possible moving around outside the stall.  In addition to reduced manure output and drier fecal matter, Williams et al 2015 found significantly reduced large intestinal motility when horses were moved from pasture to stall confinement with light exercise.

Finally, don’t neglect a combined praziquantel and ivermectin or moxidectin deworming this time of year.

Impaction colic is rarely life-threatening but causes considerable pain and often runs a prolonged course.  You can reduce your horse’s risk by management that focuses on hydration, as much exercise as possible and removing parasites.

Eleanor Kellon, VMD

 

 

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Vitamin C for Horses

Vitamin C (ascorbic acid) comes in and out of supplement headlines.  As happens with many nutrients, exaggerated claims end up being made and when these eventually prove to be unwarranted the pendulum swings too far in the other direction but there is no question vitamin C plays a pivotal role in health.

GRASS

The horse’s body can manufacture vitamin C but fresh grass is a rich source and blood levels drop off in winter when on hay.

Just about everyone thinks of vitamin C in terms of the immune system and resistance to infections/”colds”.  What it actually does is protect the immune system and other tissues from free radicals generated when the immune system cells are activated.  It therefore ends up moderating friendly fire from immune system activity rather than actually preventing infection.  Another antioxidant function is the regeneration of “used” vitamin E back to an active form.

Vitamin C is also an important antioxidant in muscle cells and all body tissues.  High levels of free radicals are generated by such things as exercise and exposure to pollutants.  Horses with chronic lung disease have been documented to have low levels of vitamin C in lung fluid and supplementation shown to support normal lung function.

Vitamin C also maintains minerals forming the reactive site of enzymes in their active form, is essential to production of carnitine and norepinephrine as well as creation of normal connective tissues throughout the body including integrity of blood vessels, structural framework of bone, joint cartilage, ligament and tendons and is critical for the restitution of wounds and injuries.

Most mammals, including horses, can manufacture vitamin C from glucose.  Unlike other water soluble vitamins, there can also be a limited storage of vitamin C in the body, at least in humans.  We don’t know much about vitamin C in horses.  They make enough to never suffer from full blown deficiency (scurvy) but we don’t know how much they can ramp up production in times of increased need, like injury or infection, whether they can store the vitamin or whether production decreases with age.  This uncertainty coupled with the observation that blood levels drop in stabled horses and over winter suggests some supplementation may be optimal.

Vitamin C has low toxicity, the major issue being gastrointestinal irritation and diarrhea at high doses (typically 20 grams/day or more in an average sized horse). Caution should be used in insulin resistant horses or other horses known or suspected to be iron overloaded.  Vitamin C increases bioavailability of inorganic iron by changing its electrical  charge and directly stimulating absorption. A daily dosage of 4.5 grams or less is best and has been shown to increase blood levels over time.

Supplementation is reasonable in horses with chronic lung irritation, musculoskeletal issues, infections or wounds, to support the body’s inherent antioxidant defenses and maintain vitamin C supplies for normal functions under conditions of high demand.

Vitamin C may be supplemented alone or in combination with plant and/or nutritional antioxidant ingredients such as bioflavonoids, grape seed and skin, vitamin E, berries, glutamine and N-acetyl-cysteine.

Eleanor Kellon, VMD

 

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