Fresh air is crucial to maintaining a horse's respiratory health. ©EQUUS

When considering your older horse's respiratory health, first take a look at the numbers; The average horse takes about 17 breaths per minute. By the time he reaches age 20, your horse will have inhaled and exhaled approximately 178,704,000 times. That’s a lot of breathing.

Fortunately, lungs don’t wear out. In fact, aging itself has little effect on the equine airway. Respiratory conditions are just as likely to develop in younger horses as in their older herdmates. But a chronic respiratory problem may worsen with the passage of time, par­ticularly if it hasn’t been managed effec­tively. And if an older horse develops an acute respiratory illness---pneumonia, for example---it may take him longer to recover than if he were younger.

For these reasons, it’s important to monitor your horse’s respiratory health as he grows older. Indeed, if you are as mindful of his lungs as you are of his legs, teeth, eyes and other organs, you’ll increase the likelihood that he will con­tinue to breathe easily well into old age.

The Effects of  Time
Recurrent airway obstruction (RAO, also known as heaves) is age-related only in the sense that it is rare in horses under age 5. “We don’t see it in very young horses,” says Frederik Derksen, DVM, PhD, of Michigan State University. “We don’t know exactly why it takes some time to show up, but it’s most likely related to the development of the immune system.”

Heaves is caused by airborne ir­ritants in the horse’s environment. Inhaled dust, molds and other particles travel to the deepest reaches of the lungs, triggering an allergic inflamma­tory response that leads to excess mu­cous production and a narrowing of the airways. These changes, in turn, make it harder for a horse to breathe, particu­larly to exhale.

Other than becoming excessively winded after exercise, a horse with mild heaves may seem normal. In contrast, a horse with a severe case may struggle to breathe even when simply standing in his stall. The sustained effort required to exhale can even lead to abnormal muscle development around his dia­phragm, leaving a visible “heaves line” along his flank.

Though heaves is rare in young horses, advancing age does not neces­sarily increase the risk of the condition. A horse who does not have a genetic makeup that leaves him susceptible to heaves probably won’t develop the con­dition as he grows old, says Derksen: “We have a herd of 30 older research horses here at Michigan State. They’ve been here between 10 and 15 years. About half have RAO. The horses who do not have it never develop it---no mat­ter how long we leave them in a dusty barn. The ones who do have it, however, will consistently develop heaves when exposed to irritants---sometimes within a few hours. This tells us that there is a genetic predisposition to the condi­tion and if a horse exposed to allergens doesn’t have heaves by the time he’s mature, chances are he’s not going to suddenly develop it.”

Nor does the management of heaves change with age: The first step is al­ways reducing the horse’s exposure to dust as much as possible. “Turning the horse out, wetting hay, feeding hay cubes---all of these work when a horse is 20 as well as they did when he was 10,” says Derksen.

On the other hand, says Derksen, additional measures may be required if an aging horse’s heaves haven’t been managed effectively over the years. “If heaves is left unchecked for a long time, the lungs will eventually remodel and develop scarring,” he says. “When you have these types of changes, it’s harder for the lungs to recover. That’s when you may need medications like bronchodilators and corticosteroids in addition to the envi­ronmental changes.”

In cases where medication is required for heaves, the horse’s age can play a role in treatment decisions. “Many older horses have Cushing’s syndrome,” says Derksen, “and, as a result, can be more sensitive to cortico­steroids. To avoid the risk of laminitis, veterinarians will use these drugs very judiciously. They’ll want to make sure the Cushing’s is well under control.”

Protection from Infection
Respiratory infections are not a big concern for most older horses simply because their working days are behind them. “These infections, like pleuro­pneumonia0, tend to occur when horses are traveling and competing,” explains Derksen. “The stress of being on the road and the athletic efforts, combined with being exposed to new horses and germs, can all lead to respiratory ill­ness.” Older horses, however, tend to travel and compete less. “It’s a perk of retirement for older horses,” he says. “They aren’t being shipped all over and exposed to as many new germs. You’ll regularly hear of elderly people dying of pneumonia, but that would be a very unusual way for an old horse to go.”

When an older horse does pick up a respiratory bug, however, the resulting illness may be more severe and take longer to resolve than it would have when he was younger. “The immune system of an older horse may be less effective in fighting off disease,” says Derksen. “As a result, an older horse may get sicker and be sicker longer.” While a younger horse may muddle through an infection with standard medications and a bit of rest, an old horse may need more powerful antibiotics and intensive supportive care to deal with a bout of serious respiratory illness.

In addition, the effects of an infec­tion may linger. “If there is any un­resolved airway inflammation in the lungs, cold air or a high airflow rate across it can trigger a cough,” says Derksen. An older horse may seem completely recovered as he stands around the field but start coughing if he picks up a fast trot to come in for dinner. This can go on for weeks or months until the residual inflammation is resolved.

Of course, if your older horse is still traveling, competing and meeting new horses, protect him from respiratory infections as you would a younger horse, says Derksen. “That means keep­ing up with his vaccinations, leaving him tied loosely in the trailer so he can drop his head to cough and clear his airway, not letting him drink from com­munal water troughs and preventing him from touching noses with every new horse he meets.”

Horses enter their golden years with the same or fewer respira­tory risks they had as young­sters. They don’t require different or specialized care to keep their lungs in good shape. If you’ve managed your horse wisely before, you’ll be in a good position to continue maintaining the health of his airways.

Respiratory Medications
A number of drugs are useful in the treatment of equine respiratory disorders:

Antihistamines: These medications act by reducing the immune system’s reaction to irritants, reducing airway inflammation. Although antihistamines help control allergy-related respiratory disease in people, they are effective in only about 10 percent of horses. They are, however, extremely safe, so your veterinarian may give them a try in case your horse is one of the few who can benefit.

Corticosteroids: These powerful medications control the inflammatory response in the horse’s lungs. Dexamethasone has been shown to be particularly effective at improving lung function, producing dramatic results within three days.

Corticosteroids can be given orally, but the preferred method of administration is through an aerosolizing mask, which delivers medication directly where it is needed and reduces the potential for systemic side effects. Because of the associated risk of laminitis, corticosteroids are given cautiously and only after environmental changes have not produced results.

Bronchodilators: These drugs, such as clenbuterol and albuterol, relax smooth airway muscles, “opening” the airways. Various forms are administered orally, intravenously or inhaled through an aerosolizing mask or device. Bronchodilators are often given to open the airways 15 minutes before inhaled corticosteroids are administered, increasing the distance they can travel into the lungs and, therefore, their efficacy.

Antibiotics: In cases of bacterial respiratory infections, a veterinarian will prescribe an antibiotic effective against the causal organisms. She may also prescribe antibiotics in cases of viral infections to prevent opportunistic bacteria from flourishing while the horse’s immune system is compromised.

Note: Nonsteroidal anti-inflammatory drugs (NSAIDs), such as phenylbutazone and Banamine, aren’t used in the treatment of respiratory disease because they inhibit a prostaglandin that protects the airways against bronchospasm.

Unexpected Dust
Poor quality, moldy hay is the obvious culprit when it comes to causing equine respiratory problems, but there are many more sources of airway irritants lurking around the barn:

• Riding rings. If you leave the arena with a visible layer of dust on your body, the air in that space is unhealthy for you and your horse. Use water or footing additives to reduce arena dust.

• Haylofts. Tossing flakes into stalls from an overhead loft is convenient, but with each meal, a storm of dust will rain down on the horse. Toss hay only when the stalls are empty, or move hay to a lower level and place it neatly in stalls.

• Leaf blowers. These machines stir up dangerous amounts of dirt and dust, blowing it directly to the level of horses’ noses, where it can hang in the air for hours. Never use a leaf blower when horses are in the barn. Instead, sweep aisleways when they are out in the fields.

• Pelleted feeds. A scoopful of feed dumped into a feed bucket can create a tiny cloud of dust as it lands. This would be a minor issue if horses didn’t wait eagerly with their noses in their buckets as meals are delivered. Scoop out grain and let it settle before giving horses access. Better yet, pour the grain and then spritz it with a bit of water, letting the horse eat it while it’s still damp.

• Bedding. Poor quality, musty straw and sawdust can irritate sensitive airways. A good choice of bedding for a heavey horse is clean, large wood shavings.

If you spend much time around horses, sooner or later you’ll encounter dimethyl sulfoxide (DMSO). After all, this pungent, syrupy liquid is used to treat a variety of equine health problems ranging from orthopedic inflammation to neurological injury.

Yet DMSO’s route to acceptance in equine veterinary care has been far more circuitous than that of most therapeutic substances. For starters, it was developed not in a pharmaceutical laboratory but from the industrial wastes of paper manufacturing. Initially, it was considered a potential miracle drug: “My first experiences with DMSO were in the 1960s,” says Barney Fleming, DVM, of Custer, South Dakota. “At that time it was considered something magic and everyone wanted to stick their finger in it.” But within a few years, the use of DMSO ceased entirely, in the wake of safety concerns. In the decades since, especially after it was approved for use in horses in 1970, DMSO has gradually gained renewed acceptance.

“DMSO is not just another medicine; we’re looking at a whole new therapeutic principle,” says Stanley W. Jacob, MD, of the Oregon Health and Science University medical school, who was the first in the United States to investigate the medical potential of DMSO. “A medicine treats a particular disease. A therapeutic principle is a new method for treating diseases in general.”

In other words, DMSO doesn’t just have specific effects on the body; its actions can also help other treatments work better. “DMSO is an economical therapy, and many people who have used it over the years swear by it and feel that it is a great help for many medical conditions,” says Fleming.

However, DMSO is a powerful agent that must be used with care. “DMSO is a relatively safe product when properly applied, but it can be harmful if misused,” says David McCarroll, DVM, DACVIM, of Interstate Equine Services in Goldsby, Oklahoma. “The best thing to do is use it under the direction of your veterinarian.”

Solvent to solutions
DMSO’s remarkable versatility as a therapeutic agent comes from its molecular structure, which allows it to interact with water in unusual ways. “DMSO is literally water’s alter ego,” said Jacob in a lecture to the American College for Advancement in Medicine in 1980. Because DMSO and water molecules are similar in shape, size and polarity, they share three important properties:

• DMSO and water blend together extremely well, at all concentrations. “The DMSO-water bond is 1.3 times stronger than the water-water bond,” said Jacob, in his 1980 lecture.
• Water has two and DMSO has six hydrogen atoms that act like magnets to dissolve and “hold onto” large quantities of complex organic molecules without binding with them or changing their structures.
• In the body, DMSO can pass through cell membranes as readily as water does without damaging the tissues, and it can replace water molecules within many bodily fluids. And, because DMSO so readily dissolves other molecules, it can also carry them through the cell membranes with it. “DMSO alters cell membrane permeability,” says Jacob. “It moves through membranes and substitutes for water so that it pulls substances through cells that ordinarily would not move through them. This is its basic mechanism of action.”

An indication of this action lies in that distinct taste DMSO causes in your mouth after it touches your skin: “When applied topically or by IV, DMSO goes into the blood quickly and is excreted through the lungs, giving the breath a garlic or burnt-almond smell,” says McCarroll. “People need to be aware of this when they use it, so they won’t be surprised.”

These properties, along with a few others, account for the ways DMSO is currently used in veterinary medicine.

Anti-inflammatory action
In horses, DMSO is applied as a topical gel or administered in liquid form intravenously or through a nasogastric tube. It is classified as a nonsteroidal anti-inflammatory drug (NSAID) because it has antioxidant properties that can interrupt the inflammatory process. DMSO binds readily with hydroxide (OH) and other “free radicals,” which are oxygen compounds that can damage or destroy healthy cells. Free radicals are often a byproduct of inflammation, and as they build up, they can stimulate more swelling and inflammation, which produces even more free radicals. Studies have shown that DMSO is a powerful free radical scavenger, and can slow or halt the destructive cascade of inflammatory damage to healthy tissue.

DMSO gel is sometimes applied topically to reduce swelling and inflammation associated with strained muscles and soft tissue injuries. Because the chemical is hygroscopic---meaning it attracts and binds to water molecules---it draws excess fluids out of tissues. “It makes a great sweat for swollen legs because it reduces edema,” says Fleming, who frequently uses DMSO in his work with endurance horses. Liquid DMSO injections may also be used to treat bowed tendons and other injuries of dense tissues that are difficult to reach with other drugs.

In addition, DMSO is also often administered orally or intravenously in the early stages of laminitis to arrest inflammation in the soft tissues of the hooves. “The toxic effects that are taking place in the feet of the horse can be relieved considerably by administering a 10 percent solution of DMSO, adding it to the IV fluids,” says Fleming. “It enhances the elimination of the toxins and reduces the damaging changes taking place in the foot.”

Finally, DMSO is sometimes prescribed to treat brain or spinal inflammation associated with trauma, oxygen deprivation or diseases such as West Nile encephalitis or equine protozoal myeloencephalitis (EPM). “DMSO does two things; it reduces inflammation, and since it is hydrophilic it also draws moisture from the tissues, reducing edema and swelling in the meninges or spinal cord, or any other tissues,” says Marlin C. Baker, DVM, of Alpha Equine Breeding Center in Granbury, Texas.

What more can DMSO do
DMSO also has wide-ranging applications that go beyond the control of inflammation:

Enhancement of drug action. When DMSO penetrates the skin and other membranes, it can readily carry many types of complex molecules with it---and that capability is often harnessed to help carry other drugs deeper into the targeted tissues. “For treating sore muscles, we just add DMSO to dexamethasone or prednisolone or any other drug we want to get inside the tissues as an anti-inflammatory,” says Fleming. “When you rub those drugs over the skin they only work topically, but if you add DMSO to them, they go into the tissues and work better.”

DMSO can also carry other drugs into tissues that are otherwise difficult to penetrate. For example, some skin infections, such as ringworm, rainrot or scratches can be hard to treat because the infective organisms can be deep under the skin or crusty scurf. DMSO can help other antifungal or antibacterial drugs reach their targets more effectively.

Not all drugs work well with DMSO, depending on their molecular weight, shape and electrochemistry. And DMSO will not carry bacteria or viruses across cell membranes because they are too large.

Pain relief. Research shows that DMSO slows or blocks conduction of impulses along nerve cells, which in effect reduces pain from musculoskeletal injuries, postoperative incisions and other sources. Relief is only temporary---lasting up to a few hours---because as the DMSO dissipates, normal function returns. However, DMSO is also often used in conjunction with other analgesic drugs to produce more long-lasting pain relief. “We also use it as an adjunctive therapy in intestinal surgeries and for analgesia postoperatively,” says McCarroll. “Many surgeons use DMSO in postoperative colic cases to improve microcirculation around the bowel. This promotes better healing and also gives some pain relief.”

Diuretic action. Because DMSO draws fluids from tissues, it may be administered intravenously in cases where it is necessary to increase the horse’s urinary elimination, such as to flush toxins from the system faster. “We use it for cantharidin poisoning [blister beetle toxicity],” says Baker. “In this situation it is given intravenously, to lessen the effect of that toxin on the kidneys and GI tract.”

Some veterinarians also routinely administer low levels of intravenous DMSO to horses who are tying up, experiencing massive cramping of the large muscles after exercise. “By giving it intravenously, with fluids, it also helps the horse urinate more,” Baker says, which in turn both helps the horse flush out and excrete the waste products from the breakdown of muscle cells and increases blood circulation into the area.

DMSO may be used to draw fluids out of the lungs in cases of acute pulmonary edema. “It is beneficial in respiratory disease because it reduces inflammation and draws some of the fluid/edema out of the lungs,” says Baker. “Along with DMSO, we use Banamine or some kind of corticosteroid (to also reduce swelling and inflammation) and sometimes it’s hard to tell which one is doing the most good, but they seem to work well together to gain a better response.”

Inhibition of microbial growth. DMSO is a bacteriostatic agent, which means it inhibits the reproduction of bacteria but doesn’t necessarily kill them outright. Some veterinarians add it in low concentrations to flushes used to rinse out draining abscesses or other infected wounds. Baker uses DMSO when he flushes out guttural pouches: “It’s not irritating when it’s diluted enough, and it does help liquefy a lot of the heavy, purulent material that is often found in the guttural pouch.”

Prudent precautions
Because DMSO carries molecules through the skin and into the body, it’s important to make sure the skin is clean and free of any other chemicals that could be inadvertently carried into the bloodstream. Fly sprays, for example, are safe when used as directed on the skin, but they contain chemicals that could become toxic if they are absorbed into the body.

“[DMSO] should not be used in conjunction with any organophosphate or cholinesterase-inhibitor insecticides,” says McCarroll. “If a person applies one of these types of fly repellents and uses DMSO, this can have an additive effect and cause toxicity. The insecticide or parasiticide would have been fine used alone, but when combined with DMSO it will potentiate or increase the effects of that drug and make it toxic to the animal.”

Many liniments also contain ingredients that are toxic if taken internally. “You don’t want to use [DMSO] with certain types of products, such as those that contain mercury salt,” says McCarroll. “This would take the mercury into the horse and can cause a fatal mercury toxicity. Iodine is not as toxic to the horse, but could also cause a problem. Certain other drugs like alcohol, insulin, corticosteroids and atropine may be made more powerful if used concurrently with DMSO.”

This ability of DMSO to ease absorption of other topical products is also an issue if a horse is to be drug-tested for competition. “There is a relatively new nonsteroidal anti-inflammatory drug called Surpass that is designed to be used topically,” says McCarroll. “When used according to directions it will not cause a positive drug test. But if you combine it with DMSO the drug level will be too high within the body and will cause a positive test.”

Because DMSO is a powerful diuretic as well as a vasodilator, it can be harmful when given to dehydrated horses and those in shock. “It can increase loss of fluid via the kidneys and further dehydrate the animal,” says McCarroll. “It also dilates the peripheral blood vessels and can thus lower the animal’s blood pressure. If the animal is in shock, this would make the condition worse.”Repeated or overzealous topical use of DMSO can dry out the skin, leading to scurf and scaling, redness or rash. DMSO produces heat when applied with other solutions, such as water or saline, alcohol or acetone, which can have therapeutic benefits---but too high a concentration can actually burn the skin. “In these instances it will produce a significant amount of heat and can actually cause thermal injury if a person is not careful with it,” says McCarroll.

Veterinarians often recommend mixing DMSO with Furacin ointment, which buffers it to reduce burning of the skin. Some horses may be more sensitive to this effect than others. “You also don’t want to use it on any individual that has had a bad reaction to DMSO in the past,” says McCarroll.

Intravenous administration of DMSO also carries the risk of side effects. If the concentration is too high or the solution is administered too quickly, muscle tremors, diarrhea, colic, seizures and/or other adverse reactions may occur. Large intravenous doses may also destroy red blood cells and inhibit clotting.

February isn’t the most inviting month for walking your bleak, frozen pastures, but if winter brought snow, ice or high winds to your area, now’s the time to check your pasture fences and ensure your perimeter is secure. And although it may be tempting to saddle up for this task, it’s best to walk the fence line instead---you’ll be better able to spot needed repairs. Here are some things to look for:

• broken or weakened fence boards
• slack smooth steel wire fencing in need of tightening or refastening
• loose or projecting nails
• wobbly posts or support braces
• sagging gates
• frayed, broken or inoperable electric fences. Use a fence tester to make sure they’re “hot.”
• downed tree limbs, especially from toxic red maple or cherry trees, and other hazardous materials.

If the fence is structurally sound or you have an alternate pasture for your horses, you may be able to put off addressing any problems you find until the weather improves. But assessing the damage and making your “to do” list now is an important first step to a permanent fix.

My veterinarian said that it is possible the bumps are old reactions to insect bites that may have flared up. It worries me to think that riding might be causing my horse pain. What can these bumps be and what can I do to treat them?

Photo © EQUUS Magazine. All Rights Reserved.

Answer: Your veterinarian is suggesting that your horse may have eosinophilic granuloma---a hypersensitivity disorder of the skin that is also called nodular collagenolytic granuloma, acute collagen necrosis or nodular necrobiosis. Variations of this disorder also occur in dogs and cats as well as people.

Eosinophilic granuloma is the most common nontumorous nodular skin disease in horses, and it is characterized by distinct bumps caused by the breakdown of collagen in the middle layer of the skin. Single or multiple nodules may occur, most commonly on the back, withers and neck. They are round, elevated, firm and well-defined, and the overlying skin and hair coat appear normal. Usually, they are not painful or itchy, unless they are irritated by tack or rubbing by the horse. The condition can occur in horses of any age, breed or gender, and diagnosis is based on history, physical examination and skin biopsy.

Why these nodules develop is unknown, but there are many theories. Because the lesions most often begin in spring and summer, insect hypersensitivity has been suspected---in other words, the horse may be having an allergic reaction to insect saliva. Other possible causes include any combination of trauma, injections with silicone-coated needles, body clipping and irritation from saddle pressure.

The most conservative treatment option is to leave the nodules alone since they generally don’t bother the horse. I would suggest applying insect repellent and keeping your horse covered with a scrim sheet to deter biting insects. However, if the bumps continue to enlarge or if they get in the way of tack, they can be injected with a steroid, such as cortisone, to shrink them. These injections are typically repeated at two-week intervals. Lesions that are still present after three injections will probably require surgical removal.

These nodules may or may not be why your mare resents being saddled. Eosinophilic granuloma does not usually cause pain unless the bumps are irritated by, for example, a saddle or pad---which may be the case here, since you mention that the ones on your mare are tender after she is ridden. I might suggest trying different equipment to see if that makes a difference.

But overall, I’d recommend that you have your mare’s lesions biopsied---especially the one on the girth area because it’s in an atypical location and may be unrelated to those on her back. Only by determining exactly what the nodules are will your veterinarian be able to prescribe the most appropriate treatment. Then, if your mare continues to resent being saddled, I’d suggest you investigate other possible causes of back pain.

Steve Adair, MS, DVM, DACVS, DACVSMR
University of Tennessee–Knoxville
Knoxville, Tennessee

There it is again---that strange-looking bump, or scruffy patch, or bald spot on your horse's skin. It looks harmless, and it doesn’t bother your horse when you touch it. But it just won’t go away.

Is it something you can safely ignore, or do you need to treat it? The answer depends on whether the spot or bump in question is caused by a bacterial, fungal or viral infection, an insect bite, sunburn, allergic reaction, bruise, abrasion or any number of assaults the world can throw at a horse.

The good news, says William H. Miller, VMD, professor of dermatology at Cornell University, is that many equine skin diseases and conditions are not very serious. In fact, some issues are considered merely cosmetic and may be left untreated, and in many cases, a knowledgeable horse owner can safely handle the situation on their own.

But there’s a catch: In order to treat a condition effectively, you need to know for sure what it is, and some issues that stem from completely different causes can look remarkably similar. Just reaching for your favorite ointment and applying it to the skin can do more harm than good. Heavy salves like Vaseline, for example, can plug hair follicles, and many homemade remedies can irritate skin.

What’s more, says Miller, persistent skin problems are rarely just skin-deep. “Skin diseases can be indicative of a compromised immune system brought on by poor nutrition, age or other disease,” he explains. So no matter how basic your horse’s skin problem may seem, if it doesn’t respond to treatment or continues to recur, talk to your veterinarian. Not only can she confirm the identity of the issue, she will help you develop a treatment plan that may include dietary and management changes and possibly systemic drugs in addition to topical treatments. And in any case, if you’re unsure what you’re seeing or how to handle it,
it’s always best to consult with your veterinarian.

But if you’re looking at one of these eight common equine skin ailments, especially if you notice them early, you may be able to manage them safely on your own.

Rainrot (rain scald)

• Appearance: scabby crusts that form raised bumps with upright tufts of matted hair. The crusts form on
  parts of the body that are chronically damp---often along the topline and where rain runs off down the barrel, shoulders or hindquarters, but also on the lower legs or faces of horses who regularly stand in mud or graze tall, wet grass. Over time, the crusts peel off, leaving small, round bare spots; pus may also be seen under newly sloughed scabs.
• Causes: Rainrot is a bacterial infection. The causative organism, Dermatophilus congolensis, can reside on the skin without causing trouble, but it multiplies rapidly in a moist environment. If the bacteria find a break in the skin, whether a small wound or insect bite, an active infection can develop. Anything that compromises a horse’s immunity---advanced age, malnutrition, illness---can make him more susceptible to the infection, as can having a heavy winter coat, which tends to trap moisture against the skin.
• Do I need to treat it? Yes. Rainrot is uncomfortable, if not painful, for the horse, and it can cause unsightly patches of hair loss.
• Treatment: First remove the horse from wet conditions and place him in a living arrangement where his coat can dry out thoroughly. A variety of anti-microbial shampoos and disinfectant rinses are available over-the-counter that are labeled for use on rainrot infections; the horse’s coat will probably need to be treated daily for at least a week. The specific duration of treatment depends on the product being used and the severity of the infection. Spot treating may be effective if only a small area is affected; otherwise, giving the horse a full bath may be advisable.
  Picking off loose scabs may help them heal faster, because exposing the bacteria to air helps to kill them, plus it will enable topical treatments to penetrate further. But do not remove scabs if they are still tight and pulling on them causes the horse pain.
  Call your veterinarian if an infection fails to improve after a week, despite treatment. She can make sure your horse actually has rainrot, rather than another similar condition, and may prescribe a topical medication or oral antibiotics, especially if a secondary infection has set in.
• Prevention: Provide dry areas that turned-out horses can retreat to in wet weather and keep your run-in shed’s roof in good shape. Waterproof blankets and light sheets can also help keep pastured horses dry; just make sure their coats are not damp when you put them on. Groom often, both to clear away mud or dirt, which can hold moisture against the skin, and to spot the infection in its earliest stages. Disinfect all blankets and equipment that came in contact with an infected horse before reuse.

Ringworm (fungal dermatitis)

• Appearance: rounded hairless patches with crusty, scabby skin. The lesions are most common on the face, neck, shoulders, chest or under the saddle or girth, but they can appear anywhere on the body. The affected areas may be sore or itchy, but they often cause no discomfort, and the horse may appear otherwise healthy.
• Causes: Despite the name, ringworm is a fungal infection, which can be caused by several organisms, usually members of the Trichophyton or Microsporum families. The fungi, called dermatophytes, consume keratin, the protein that forms the structure of hair and epidermal skin cells. The fungi can survive for months in the environment, on tack or fences, and they can be carried on the skin for up to three weeks before signs of infection are evident---during this time, the fungi can be easily spread to other animals, and sudden outbreaks may affect every horse in a herd.
• Do I need to treat it? Yes. Left untreated, the lesions will continue to grow and spread. Although infections might heal eventually on their own, the horses would be highly contagious until they do.
• Treatment: If you suspect ringworm, immediately isolate the affected horse from all other animals, including cats and dogs as well as other livestock. Clipping the hair around the lesions and removing scabs and crusty material as much as you can without causing the horse pain will reduce the organisms’ food source. Several over-the-counter antifungal medications, as well as some human dandruff shampoos, may be effective against ringworm, but you may need to try several products to find one that works best for your horse. First clean the area with a general antifungal antiseptic, such as chlorhexidine, then dry thoroughly before applying an antifungal ointment or medication. Repeat the treatments until the infection is resolved. Exposure to air and sunshine will also help kill the fungi.
  Call your veterinarian if the lesions continue to spread or the horse’s skin does not appear to be healing after a week. She can confirm that the infection is ringworm by scraping off a few skin cells and examining them under a microscope for the presence of fungal spores. If the case is severe or if you are handling many cases at once, your veterinarian may prescribe oral medications that can be used in combination with the topical washes.Prevention: Keep separate tack, equipment and grooming supplies for every horse in your care, and do not share with others at shows or events. Quarantine new horses brought to your farm for at least two weeks to make sure they aren’t carrying ringworm or other contagious diseases.
  In the case of an outbreak, clean and disinfect any tack or equipment as well as wash stalls and fences in communal areas that other animals may have had contact with. Use a power washer to get disinfectant into all the crevices. Remember that people can get ringworm as well as all your other animals, including cats and dogs. Always wear gloves when handling infected horses and exposed equipment.

Warts (papillomas)

• Appearance: raised gray or pink cauliflower-like growths that are usually fairly small, not much bigger than peas. They may appear singly or in clusters, most commonly on the muzzle or around the eyes but also occasionally on the ears, genitals and lower legs. The growths do not appear to cause any pain or discomfort.
• Causes: Warts are caused by the equine papillomavirus, an organism that can survive on skin, equipment and structures for weeks. Younger horses, under 3 years of age, are more susceptible, although warts can appear in adults.
• Do I need to treat it? No. The warts are harmless, unless they are inhibiting the horse from eating, blinking or moving or they are interfering with tack.
• Treatment: Left alone, the warts typically shrink and disappear, leaving no scars, over the course of about four months as the young horse’s immune system develops. They are likely to persist for a year or more when they appear in older horses. Warts that need to be removed can by excised with laser or cryosurgery, but these procedures may leave scars. Drugs that stimulate immunity may also be helpful.
  If warts do not go away on their own, have your veterinarian examine them; other diseases and conditions, including some sarcoids, can look very similar to papillomas.
• Prevention: Isolate affected horses from others, especially younger ones. Disinfect any shared tack or equipment.

Aural plaques (papillary acanthoma, ear papillomas)

• Appearance: flat, crusty, raised white lesions inside the ears; underneath, the skin may be pink and sensitive. Aural plaques usually cause no pain and are considered to be just a cosmetic problem. But biting flies may irritate the lesions, and some horses may begin to resist bridling or having their ears handled. Both ears are likely to be affected. They are not likely to shrink or go away on their own.
• Causes: Aural plaques are caused by an equine papillomavirus that is thought to be spread by biting flies, such as the blackfly, that target the ears. The plaques may appear in horses of any age or breed.
• Do I need to treat it? No, unless the plaques are bothering the horse.
• Treatment: Most horses resent having the plaques physically pulled off, and doing so can inflame the ears and make the problem worse. If the plaques are causing ear sensitivity, your veterinarian may prescribe a course of treatment with a topical cream containing imiquimod, a drug that stimulates a localized immune response in the ear and helps diminish the lesions.
• Prevention: Take precautions to protect your horse against biting flies, especially blackflies. Use fly spray, and outfit your horse with a fly mask that includes ear coverings. Also use ear covers that can be worn with a bridle, especially if you ride in wooded areas near water. Stable your horse at dawn and dusk, when blackflies are most active.

Primary seborrhea (dandruff)

• Appearance: Seborrhea can be dry or oily. In the dry form, small flakes of skin appear routinely, usually at the base of the mane and tail, and sand-like flecks may appear on the girth area or anywhere sweat accumulates. Oily seborrhea causes large, waxy crusts, often on the elbows, hocks or lower legs; when peeled off, these may leave hairless patches up to several inches in diameter. Dandruff sometimes causes a fetid odor, but the horse is not usually itchy or in pain.
• Causes: Heredity plays a significant role in cases of primary seborrhea, and it is more common in Arabians and Thoroughbreds. In affected individuals, dandruff is likely to be a lifelong issue.
  Please note, however, that primary seborrhea looks just like secondary seborrhea, which can also be either oily or dry. The biggest difference is that secondary seborrhea develops in horses who had not previously experienced the condition, although the onset can be very gradual. Secondary seborrhea is a sign that can accompany several potentially serious illnesses, including liver or intestinal disease.
• Do I need to treat it? No, but most people prefer to do so for aesthetic reasons. Consult your veterinarian if your horse develops seborrhea or if a mild case seems to be getting significantly worse with no obvious explanation.
• Treatment: Primary seborrhea is not curable, but it can be managed. A number of antidandruff shampoos are available that, when used as directed, can dissolve flakes and loosen oily scales. It’s best to choose products formulated for use on horses; human products can be too harsh. Gentle scrubbing with a soft- to medium-bristled brush can help remove crusts. If you have difficulty controlling a stubborn case, talk to your veterinarian, who may recommend other topical medications. She may also suggest performing diagnostic work, such as blood tests, to rule out other causes. Secondary seborrhea is likely to clear up when the underlying disease is treated.
• Prevention: Regular grooming stimulates circulation and natural oil production that help keep the skin healthy and clean. Feeding vegetable oils, especially omega-3 fatty acids, and supplements that contain biotin may also help promote healthier skin. Talk to your veterinarian or an equine nutritionist before making changes in your horse’s diet.

Eosinophilic granuloma with collagen degeneration (nodular collagenolytic granuloma, nodular necrobiosis, or simply nodules)

• Appearance: distinct, firm nodules about the size of a dime or smaller, found usually in the neck, back and withers. Several small nodules may cluster together to form what appears to be a larger lump. The skin above is normal, with no hair loss, and the nodules do not contain pus. The bumps can occur in horses of any age, breed or gender. They usually are not painful or itchy, unless they’ve been irritated by rubbing. Over time, they may mineralize, which makes them feel harder.
• Causes: The nodules are caused by the breakdown of collagen, the protein that forms the structure of connective tissue, in the middle layer of the skin. Why this happens is not fully understood, but the inciting event is believed to be hypersensitivity, when the immune system overreacts to the presence of some allergen and creates a “mass” to contain it. Allergic reactions to insect bites are thought to be the most common cause of these nodules, but injections with silicone-coated needles, minor scratches from body clipping and other traumas may be responsible in some cases.
• Do I need to treat it? No, the nodules are harmless, unless they are interfering with tack or continuing to grow in size because the horse is rubbing them.
• Treatment: Your veterinarian can inject corticosteroids into the nodules to shrink them. If the nodules are still present after three or more injections, which are usually given at two-week intervals, she may suggest surgical removal. The nodules become more difficult to treat medically once they have calcified, so some veterinarians may recommend more aggressive treatment earlier after they appear.
• Prevention: Take measures to protect your horse from biting flies, including the use of fly sprays and turnout sheets. If your horse has developed nodules at injection sites, ask your veterinarian to use noncoated needles for future injections.

Mange

• Appearance: small, round bumps at first, soon followed by bald spots, with scaly, thickened skin, usually on the lower legs of draft horses with heavy feathering, although any horse can be affected. In more serious cases the skin may be rubbed raw and show signs of secondary infections. Mange causes itching, and horses will rub, stamp and bite at their legs. In rare cases, mange may appear on other parts of the body.
• Causes: Mange is a parasitic infection caused by several species of tiny mites that can barely be seen by the naked eye. The most common form that occurs in horses in the United States is chorioptic mange, caused by the mite Chorioptes equi, which typically affects the lower legs of horses with feathering. Although rare, horses may also develop psoroptic mange (Psoroptes equi), which produces lesions under the mane and tail, under the jaw and in the groin and armpits, and demodectic mange (Demodex equi), over the face, neck and shoulders.
• Do I need to treat it? Yes. Not only is mange uncomfortable for the horse, it can cause permanent thickening and scarring of the skin that can impede the movement of the pastern joints.
• Treatment: A number of topical antiparasitic products can be effective against mange---look for products that contain lime-sulfur solutions, organophosphates or permethrins, which can be applied by spraying, sponging or dipping the leg. Administering oral ivermectin or moxidectin may also be helpful in some cases. Treatments may need to be repeated three or four times at 12- to 14-day intervals. Clipping the legs will help the topical treatments reach the skin but may not be necessary in all cases, especially if the infection is still mild.
  Call your veterinarian if the infection is severe or does not respond to treatment. She can examine skin scrapings under a microscope to confirm the presence of the mites, and she may suggest an alternative treatment. Oral antibiotics may be necessary to treat secondary infections.
• Prevention: Mites usually are passed directly from horse to horse, so do not allow your horse to have contact with others at shows or events and quarantine newcomers on your farm, especially if they have visible bald areas that appear to be itchy. Some horses can carry the mites without showing signs of infection and can be a source of recurrence after other horses are treated. If you have an outbreak, it’s a good idea to treat all horses who have been in contact with the ones affected and change out all of the stall bedding used by affected horses.

Lice (pediculosis)

• Appearance: hair loss from rubbing, usually appearing first on the shoulders and neck, as well as on the head and the base of the mane and tail. Affected areas are intensely itchy and may also have abrasions and scabs from rubbing and possibly secondary infections. Flattened insects up to two to four millimeters long may be visible if the hair is parted and the skin examined in good light. Pale, translucent eggs may be attached to nearby hairs. The horse is also likely to be generally unthrifty and in poor health. Lice infestations tend to be more severe during the winter months but can occur at any time of year.
• Causes: Two types of these parasitic insects infect horses: Chewing lice (Damalinia equi) feed on sloughed-off dead skin cells; these are more likely to affect the neck, flanks and the base of the tail. Biting or sucking lice (Haematopinus asini) feed on blood; this species prefers longer hair and may be found under the forelock and mane, the tail and on the pasterns of long-feathered horses. Both types cause skin irritation and itching.
• Do I need to treat it? Yes. Not only is a lice infestation extremely uncomfortable for the horse, severe cases can cause anemia.
• Treatment: Several types of products---permethrin sprays and wipe-ons, insecticidal powders and shampoos---are effective against lice. Read and follow label instructions and precautions carefully. Many treatments need to thoroughly coat the skin to be effective, but some products may irritate small cuts and abrasions. Oral ivermectin may be effective, but only against the biting lice. Because the insecticides will not kill eggs, the treatment needs to be repeated in two weeks to eliminate newly hatched adults.
• Prevention: Lice can be passed directly from horse to horse, as well as via shared tools and equipment. Isolate affected horses as well as those who have been exposed to them.
• Louse eggs that detach from the horse’s coat can hatch and re-introduce the infestation, so it is important to clean and sterilize any tack and equipment that was used on the affected horse. Clean brushes and small tools with an insecticide, or boil items that will not be damaged by heat. Pads and blankets can be sterilized by machine washing and drying at a high heat setting. Also spray or scrub down stall walls or paddock fences and change the bedding.

Question: I’m worried that a weed that grows on my property may be horse nettle, and I’d like to know more about what this plant can do and how to identify it. I know it’s poisonous for horses, but how much do they have to ingest for it to be harmful? Is there a cumulative effect?

Answer: Horse nettle (Solanum carolinense), also referred to as Carolina horsenettle or bull nettle, is a member of the nightshade family and is found in most of the contiguous United States but especially in the Central and Eastern states.

The plant grows up to two feet tall, with an erect, branching structure; the leaves are alternate and can grow to four to six inches long, with irregular wavy or lobed margins. The leaves and stems are often covered with fine hairs and prickly spines. The flowers, which appear at the top of the plant from June through August, are three-quarters to one inch across and range from light purple, blue to white. The plant produces round, tomato-like berries that are half an inch in diameter and change from green to yellow as they ripen.

Horse nettle, like many plants in the nightshade family, contains solanine, a glycoalkaloid that irritates the oral and gastric mucosa and affects the autonomic nervous system, which controls various internal organs. The glycoalkaloids act on the digestive system to cause excessive salivation, colic and diarrhea or constipation. These signs may be followed by depression, weakness, depressed respiration, dilated pupils, collapse and death if horse nettle is eaten in large amounts.

All parts of the plant are poisonous, but toxicity varies depending on growing conditions. The glycoalkaloid levels are higher in the fall than in the spring, and green, unripe berries are more toxic than ripe or dried berries. Toxicity is reduced (but not eliminated) when the plant is dried.

Any livestock---including cattle, sheep, goats and pigs as well as horses---may be poisoned after eating large quantities of horse nettle. Horses tend to avoid the plant because it is distasteful, and they are unlikely to eat enough to cause serious problems unless the weed is rampant in their pasture or they have no other suitable forage. The amount of horse nettle it takes to produce a toxic effect varies, depending on how concentrated the solanine isin the plant, and how much is eaten. However, it generally takes a pound or more to cause poisoning. A single mouthful or a few berries will have little effect on a mature horse. The glycoalkaloids act rapidly once they are absorbed from the intestinal tract, but the effects are not cumulative.

Eradicating established horse nettle is difficult. The plant propagates from seeds, and it also spreads through an extensive underground root system. Mowing the plants before they produce seeds will slow them down but won’t eliminate them. And because they can grow back from even small portions of their rhizomatous roots, they are difficult to control with herbicides or by pulling them up manually.

Contact your local extension agent to identify the plant and for tips on the best strategies to control it in your area.

Anthony P. Knight, BVSc, MS, DACVIM
College of Veterinary Medicine & Biomedical Sciences
Colorado State University
Fort Collins, Colorado

You know it’s important for your horse’s saddle and bridle to fit correctly. But don’t forget to make sure his bit fits, too. A bit that’s too small can pinch the corners of the mouth, while a bit that’s too big can move around too much and clunk against his teeth. Rubbed patches or thickened skin at the corners of the mouth are signs of bad bit fit, but it’s better not to wait to see physical evidence that a bit doesn’t fit well.

To test whether a bit is the proper size for your horse, you need only an ordinary piece of twine and a ruler or tape measure:

• Guide the twine into the horse’s mouth and back toward the corners so that it is positioned approximately where the bit would lie.

• Pull it taut and use your fingers to grasp it at each corner of the lips.

• Remove the twine and use your ruler to measure the length between your fingers.

The general rule is that a properly fitted bit measures a quarter-inch longer than the width of the horse’s mouth. You can adjust the cheek pieces of the bridle to make sure that the bit rests properly in the bars of the mouth, creating one or two wrinkles at the corners.

In addition to width, the overall shape of a horse’s mouth, including the hard palate and the size of his tongue, can influence the size of bit he needs. This means that a thicker bit is not always milder. And, as a horse ages, the contours of his mouth may change, so the bit you use now may not be comfortable for him in 10 years. It’s easy to start second-guessing your current bit, but don’t worry: If your horse is happy and responsive, chances are it fits just fine. If you’re concerned, you can always ask your veterinarian to evaluate it.

In the soggy months between winter and summer, your horse pastures can quickly turn into a muddy mess. Short of moving to the desert, you’re not likely to escape mud entirely, but you can take some practical pasture-management steps to minimize the worst of it:

• Pick up manure regularly. A single horse can produce up to 50 pounds of manure per day. Add ample spring rains, and it’s easy to see how turnout areas can quickly become a muddy mess. Remove manure from pastures and paddocks at least every two to three days.

• Avoid overcrowding. When too many horses are placed in a small area, their hooves churn up the ground, killing the grass and turning the area into mud. One option is to bring all your horses into a designated “sacrifice area” to protect the grass in your larger turnout during the wet season. But if you have the space, limiting the number of horses per paddock to one or two will help keep the grass intact and reduce mud.

• Install dry footing. High-traffic areas at the gate or feeders are likely to become wet and slippery. Try laying down gravel, wood chips, hog fuel, sand or some other material that will provide safe footing while allowing water to drain through.

• Inspect your runoff system. Make sure the gutters on your barn and sheds are clear of debris and redirecting rainwater well away from the foundations. Ideally, they’d send runoff into low-traffic areas with enough vegetation to capture and absorb the water.

• Plant “rain gardens.” A buffer zone of plants around pastures as well as driveways and other hard surfaces will help capture rainwater and reduce runoff problems, including mud. The best plants for rain gardens are deep-rooted wildflowers, small trees or shrubs local to your area; check with your county extension agent or a nearby garden center for suggestions.

You stand in the pasture and call your horse’s name, but he doesn’t raise his head and trot over as quickly as he used to. Is he just tuning you out or is his hearing starting to go?

Age-related hearing loss in horses is similar to what happens in people—tiny hairlike structures (cilia) within the
inner ear become damaged, which interferes with their ability to convert sounds into electrical signals that the brain
can interpret.

Detecting hearing loss in horses can be difficult because they are so responsive to body language, and they readily adapt to their circumstances. And, for the same reasons, deafness in a horse isn’t a serious concern—most get along just fine. Nonetheless, it is important to identify deafness so you can make allowances in how you handle and manage your horse.

Here are some ways to determine whether your horse’s hearing is impaired:

• Observe him with his herd for 30 minutes or longer. Horses rely on their hearing to track the movements of herdmates. Does he seem unaware of other horses as they move around the pasture? Is he startled when a frisky horse gallops by?

• Staying out of range of kicks, stand behind your horse while he is dozing and clap your hands sharply. A horse with normal hearing will react to the sound.

• Stand out of sight, shake a bucket of grain and watch for his reaction. Most horses will perk up at the noise.

If you need a more definitive diagnosis, contact your veterinarian. She may refer you for a brain-stem auditory evoked response (BAER) test, in which foam earpieces are placed in the horse’s ears and small electrodes are inserted just under the skin at specific points around the head.

When a series of clicks are played through the foam, the electrodes record the signals carried along the auditory nerves. The BAER test can’t determine how well a horse can hear, but it can detect total deafness.

After I lost a wonderful trail horse to a tragic accident, I was depressed and did not even want to start looking for another one. But my loyal friends, knowing how much I need a horse in my life, dragged me all over Michigan. Yet my response to every horse for sale was always, “No, thank you. Not quite right.” This went on for the entire summer of 2009.

Finally, while we were riding one day in our favorite local park, my friend and I met a couple with some very nice Quarter Horses. Casually I asked, “Do you know of anyone who might have a nice trail horse like yours for sale?” The man said he had a few, and he lived only 45 minutes away. On a very cold, windy November day, my friend and I made the trip.

I said that I really wanted a quiet horse so my granddaughter could ride too, and the man brought in from the pasture a 5-year-old Quarter Horse mare named Jodie. Her owner mentioned that she had not been ridden for a few months, so I was a bit wary. But he saddled her up, led her out into his 50-acre hay field and just hopped on. She walked right off and then he loped her around the field. Just then, a little old pony who roamed freely on the farm came cantering in and ran in circles around the mare. Jodie was unfazed and just kept loping along as nice as could be.

My friend and I took turns riding the mare, who seemed unconcerned about everything---just what I had been looking for. I purchased her the next day.

A sudden change
Jodie settled into her new home quickly. She was turned out 24-7 in a pasture with a run-in shed, keeping company with two ponies that belonged to my granddaughters. She also made an easy transition to our meal plan---grass hay to supplement the fall pasture, plus a token amount of complete feed.

The weather was beautiful, so I started riding Jodie right away at the state park. From our first outing, she was perfect. She walked out happily and freely and cantered beautifully down the trails. I rode as much as
possible that fall and through the winter and spring.

But the next summer, Jodie’s personality began to change. When I tightened the cinch, she’d pin her ears and try to bite me. I suspected the problem was back pain---she has a broad back and I’d been having a terrible time finding a saddle that fit her well. It seemed I was shipping saddles back and forth from tack shops almost every other week.

Despite my efforts to find a better saddle, Jodie got more and more miserable. In late October, she began stopping at the bottom of hills and would go up only with urging. Then one day she did not want to continue her canter. When I asked her to move on, she actually bucked and pinned her ears---this
from a horse who could have won the Miss Congeniality award just a few months earlier.

I knew this had to be more than just an attitude problem, so I called my veterinarian, Robert Renton, DVM, of Howell Animal Hospital. As he examined Jodie, it took him only a few minutes to discover the
nature of the problem: When he pushed gently on her side, she pinned her ears and tried to kick him. He carefully continued the exam and listened closely as I described the changes in the mare’s behavior.

Jodie was clearly in pain, Renton told me when he’d finished. That conclusion was easy. The difficult part would be figuring out what was causing it. My mind reeled as the veterinarian outlined what seemed like an endless list of potential causes, ranging from poor saddle fit to hock pain, ulcers and ovarian tumors.

A few of the possibilities didn’t seem likely. Gastric ulcers, for example, can cause overall grumpiness, but Jodie’s outdoor, hay-fed, low-stress lifestyle didn’t fit the profile for that condition very well. Renton also discussed a type of muscle disorder, but most horses affected with that have asymmetrical hindquarters and are on high-grain diets, neither of which was true for Jodie.

Renton suggested that I continue looking for a better-fitting saddle while we worked down the list of more probable causes of Jodie’s pain, beginning with the most likely one---her hocks. Renton took a series of radiographs of both Jodie’s hocks. Everything looked healthy and normal, but just to be sure, we started her on a course of phenylbutazone, which would reduce any pain and inflammation, to see if she would improve over the next few weeks. She didn’t.

To investigate the next possibility, Renton returned to do a full reproductive exam, including an ultrasound of Jodie’s ovaries and blood work to look for abnormal hormone levels. A growth on her ovary would be painful, and it would also secrete hormones that could explain her aggression. Once again, though, everything was normal.

And Jodie’s pain continued unabated. Things seemed to be at their worst around Christmas of that year. We had unusually nice weather just before the holiday and I slipped onto Jodie bareback to take a walk around the pasture. But the moment I sat on her, she pinned her ears, braced her back and sent me a very clear message that she hurt. I knew then it wasn’t the saddle, and I was starting to worry that my sweet mare was forever changed.

I wasn’t ready to give up, however. The next rule-out Renton suggested was equine protozoal myeloencephalitis (EPM), a progressive neurological disease caused by a parasitic infection of the central nervous system. Jodie didn’t seem particularly uncoordinated, as horses with EPM typically are, but she had started to drag her hind toes as she walked, which can be an early sign of the disease. A blood test for antibodies to the protozoa came back positive, which meant she had been exposed to the organism, as about half of U.S. horses are, but that doesn’t necessarily mean that they have the disease. Only about 1 percent of the horses who encounter the protozoa, which are consumed with contaminated feed or water, ever develop signs of illness.

To explore this possibility, we could have had a spinal tap performed. This procedure involves drawing a sample of cerebrospinal fluid from the spinal canal to look for the presence of the protozoa, but the test is invasive and can still yield false positives. What’s more, it would require taking her to a university hospital. Or, Renton suggested, we could just start Jodie on the medications for EPM and look for improvement. I opted to skip the spinal tap and begin the treatment. I had high hopes it would help. But it didn’t.

Gastric ulcers were next on our list. These painful lesions in the lining of the stomach can cause a number of subtle signs, including vague pain and touchiness, especially when being saddled. They are more likely to occur in horses kept in stalls, fed a high-grain diet and subjected to a stressful lifestyle, including travel and competition. But although Jodie lived outdoors and ate mostly hay, she did show some signs of digestive discomfort. Every morning when I went out to feed, she had moist ruffled hair on both her sides where she had bitten at herself.

Gastric ulcers can be diagnosed with an endoscope, a long tube with a camera inserted down the esophagus and into the stomach, but many veterinarians will simply administer the medication to treat ulcers, GastroGard, and watch to see if the signs of discomfort dissipate. We put Jodie on GastroGard, and after a month she did stop biting her sides, but she remained grumpy, and her body still seemed sore. In fact, if I just pointed to her sides, she would pin her ears.

By May of 2011, Renton and I had exhausted the obvious diagnoses that could be made on the farm. He suggested I take her to Michigan State University’s large animal clinic for a more complete exam. Two internists, a back specialist and a physical therapist saw her there, and together they performed a series of exams so thorough it took nearly two days to complete.

The only obvious problem they found was mild gastric ulcers, although the physical therapist also noted that Jodie’s back was oddly dipped. She wasn’t swaybacked, but it seemed as if her back muscles were weak and possibly strained by her extra weight. We were sent home with instructions to continue the ulcer treatment, begin a routine of exercises, such as belly lifts and carrot stretches, designed to limber and strengthen her back muscles, and have Jodie lose 100 pounds.

I faithfully did Jodie’s back exercises daily but saw little improvement. When I massaged or manipulated her back, she would crankily bite the cross ties. I was beginning to think that I would never be able to ride my poor mare again, but even more distressing was the thought that she’d always be uncomfortable and unhappy.

Finally, an answer
Over the Fourth of July weekend, I found myself searching the Internet for any situation that sounded even remotely similar to Jodie’s. As I clicked from one false lead to the next, I grew increasingly despondent.

Then, suddenly, I was reading a description of a horse who sounded remarkably like Jodie. This horse had suddenly turned cranky with no obvious physical reason. The owner, like me, hadn’t wanted to give up and eventually got a diagnosis: polysaccharide storage myopathy (PSSM).

This was one of the muscle disorders Renton and I had discussed briefly a year ago, but we’d decided that Jodie did not fit the profile. Well, neither had this horse I was reading about.

I immediately called Renton to tell him what I’d read, and he agreed it was worth a shot to have Jodie tested, even if the results came back negative. Currently, researchers have described two forms of this disease---PSSM Type 1, which has been linked to two specific genetic mutations that can be tested for, and PSSM Type 2, which is diagnosed by a muscle biopsy. Both tests are available only through the University of Minnesota, where much of the research on this disease has been done.

Which testing approach is recommended---the genetic test or the muscle biopsy---depends on the breed of horse. For Quarter Horses, the Minnesota researchers suggest doing the genetic test first, and by the end of the afternoon, I had received instructions via email on how to pluck mane hair and send it to the lab. Three days later I had an answer: Jodie had PSSM.

In the meantime, I’d been doing plenty of reading on PSSM, starting with the University of Minnesota’s website. I learned that many Quarter Horses, as well as more than 20 breeds, carry a genetic mutation that causes this disease (PSSM 1). Other light breeds, including Arabians and Thoroughbreds as well as some Quarter Horses, may also develop PSSM without carrying the mutated gene (PSSM 2).

Both forms of the disease affect the way muscle cells absorb, store and use the sugars they burn for energy. In horses with PSSM, the muscle tissue pulls a sugar (glucose) out of the bloodstream faster than in normal horses, according to the Minnesota researchers. The genetic mutation for PSSM, GYS1, results in overproduction of the storage form of the sugar, called glycogen, in the muscle cell. As a result, abnormal amounts of glycogen, as well as another abnormal sugar (polysaccharide), tend to accumulate in the cells. One reason for this, according to their research, is that the abnormal GYS enzyme that produces glycogen is very sensitive to insulin, a hormone released when a horse eats carbohydrates, which stimulates the muscles to take up more sugars and make more glycogen.

Horses who have inherited either one or two copies of the gene mutation may develop episodes of tying up (exertional rhabdomyolysis): painful, severe muscle stiffness and cramping in the hindquarters, usually after exercise. The muscles will feel very hard to the touch, and affected horses will resist moving their hind feet. In severe cases, the urine may be dark, brick-red or coffee-colored---a sign that muscle cells have been damaged and released proteins into the bloodstream. These proteins can damage the kidneys.

Fortunately, however, some horses like Jodie may have milder muscle pain, which is why I’d never seen signs that obvious. The downside, of course, was that her muscle stiffness and soreness were so subtle that it took
us nearly a year to figure out what the problem was.

But there was good news, too. Even in severe cases of PSSM, episodes of tying up can be prevented with careful attention to the horse’s diet and exercise. Because meals rich in starches and sugars cause insulin spikes, diets based on grass hays, with no added grains, are recommended for these horses.

Jodie got barely any grain at all, so the source of the sugars in her diet could only be our lush pasture and hay. I immediately put a muzzle on Jodie to keep her from eating any grass at all, switched her to a low-nutrient grass hay and began feeding a low-sugar, high-fat concentrate specially formulated for PSSM horses. Within two weeks she was moving much more comfortably and no longer snapped at anyone who tried to touch her.

But she still wasn’t entirely comfortable. After consulting with Renton and the University of Minnesota, I decided to discontinue the grain mixture because, frankly, Jodie didn’t need the extra calories. Within another week, her demeanor improved even more.

Regular exercise and as much turnout as possible are also recommended for horses with PSSM. This helps the muscle cells to continuously burn off the stores of glycogen they accumulate.

Jodie was already on 24-hour turn-out, but I continued doing the back exercises, and I noticed that she was beginning to lift her back and stretch more comfortably when I asked. I switched from using carrots, which are high in sugar, to celery as a lure to move her head and neck. Eventually, her topline filled in as her muscle tone and strength improved.

Once Jodie was moving comfortably, the next phase of the plan was to begin working her under saddle again. I’ll admit I was a bit anxious when I got back on her, but because she was no longer in pain, she was her old, sweet self. We hit the trails again, starting at a walk, then added short stretches of trotting. But to me it all felt as if we were flying. I cried tears of happiness the day we finally cantered and hopped over a small log.

Jodie’s PSSM wasn’t apparent when I purchased her because of the sparse fields at her previous home. Only as the sugar levels increased in our pasture over the spring and into summer did the problem arise. This past winter, the weather wasn’t cold enough to convince me the grass was dormant until mid-December, so I left Jodie’s muzzle on until then. I’ll put it back on the moment the days start to warm up again this spring.

I’ve also made one other management change. Knowing just how sensitive Jodie is to sugars and starches, I now have each batch of hay I buy tested for both. This is a lot of work, but everyone who knows Jodie knows it’s worth it. In fact, my wonderful husband even made me a hay corer for Christmas, allowing me to easily pull hay samples from the center of the bales. It was the perfect gift.