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Common Equine Parasites and Deworming Strategies
Deworming protocols are a common discussion amongst barn managers, horse owners, and veterinarians. In order to understand various deworming strategies and apply the one that works best for your horse, you have to know the common parasites that affect the horse.
In years past, Strongylus vulgaris (large strongyles) was the equine parasite of most concern. Large strongyles take approximately two months from the time they are ingested by the horse until they are shed in the manure to further contaminate the pasture. Thus the traditional rotational deworming strategy was developed and adequately controlled large strongyle infections. However, large strongyles are rarely an issue in managed horse populations today, and therefore rotational deworming is no longer needed or recommended.
Cyathostomins, or small strongyles, are considered the major adult equine parasite. Small strongyles are pervasive and infect grazing horses everywhere. Luckily, small strongyles typically only produce disease when the parasitic burden is severely elevated, although they can result in disease at lower levels if the horse’s immune system is compromised in some other way. Since low levels of small strongyles do not result in disease and large strongyles are well controlled in today’s horse populations, frequent deworming is no longer necessary, rather properly timed deworming during the seasons of heavy parasitic burden and transmission is ideal.
Anthelmintic (dewormers) resistance is becoming a problem that can be delayed and hopefully controlled with the use of fecal egg counts (FEC), proper pasture management, and appropriately timed deworming for that particular environment. Parasite refugia is a common term used by parasitologists and veterinarians that refers to the population of parasites that survive the administered anthelmintic; this includes the stages of parasites that are not affected by that drug, the parasites within the horses that were not treated, and all of the living parasite stages on pasture. The larger the proportion of parasites in refugia, the slower resistance can develop. Therefore, it is advised to perform fecal egg counts on your horses biannually and deworm according to parasitic burden so that only a proportion of the horses in the herd will be dewormed at that time rather than deworming all of the horses at once. Another management tactic to slow anthelmintic resistance is to avoid rotating pastures right after deworming as this eliminates the dilution effect. Lastly, avoiding deworming during periods of low parasite transmission/low pasture refugia is advised. Low pasture refugia occurs during periods of extreme temperatures because larvae (parasite eggs) cannot survive in harsh weather, such as the winters in the north or the summers in subtropical and tropical environments.
It is also important to understand that some horses are more sensitive to small strongyle infections, and therefore will always shed more eggs than others. In fact, 20-30% of adult horses in a herd shed approximately 80% of the total eggs. Therefore, horses are divided into three categories based upon their FEC numbers: low (0-200epg), moderate (200-500epg), and heavy shedders (>500epg). On average, if a horse’s FEC is over 200 eggs per gram (epg) then he/she should be dewormed, although individual veterinarians may have different cutoff values. Moderate and heavy egg shedders may require more frequent deworming than twice a year.
Other gastrointestinal parasites that affect the adult horse are Anoplocephala perfoliata (tapeworms), Oxyuris equi (pinworms), and Gasterophilus spp. (bots).
· >Tapeworms are spread through the ingestion of an oribatid mite commonly found on grass pastures. These mites live in moist areas, and therefore tapeworms are usually not an issue in arid environments. Tapeworms have the potential to result in various types of colic. They cause small mucosal erosions at the site of attachment, which can be painful. Also, an infection with tapeworms can result in an ileocecal impaction or a spasmodic colic if the burden is high enough. Tapeworm eggs are intermittently shed in the manure and can be easily missed on fecal floats. Therefore, it is important to deworm with an anthelmintic once a year that is efficacious against tapeworms, such as praziquantel (sold in combination with ivermectin or moxidectin) or a cestocidal dose of pyrantel pamoate. It is recommended to treat for tapeworms in the late fall or early winter.>
· >Pinworms have historically been an issue with young horses; however, they have become increasingly more common in adult horses recently. Pinworm eggs are deposited on the perineum and perianal regions and result in pruritus (an itching sensation), which can lead to intense tail rubbing and skin excoriations. The tail rubbing in addition to sharing grooming materials and tail wraps can spread the pinworms to other horses. The best way to control pinworms is to deworm when clinical disease is present. Ivermectin, moxidectin, pyrantel pamoate, or fenbendazole will eliminate a pinworm infection. Additionally, it is recommended to wash the perineum and perianal regions to provide relief of pruritus and to decrease transmission to other horses.>
· >Bots rarely result in disease but are aesthetically displeasing. Therefore, deworming annually in late fall or early winter will help to decrease transmission the following season. Ivermectin or moxidectin are the only anthelmintics available at this time that are efficacious against bots.>
Parascaris equorum (roundworms) is the primary parasite of foals and weanlings. Infections can result in poor growth, airway inflammation (cough, nasal discharge), and small intestine impactions. Small intestine impactions and subsequent fatal intestinal ruptures can occur when foals/weanlings with a heavy roundworm infestation are dewormed with an efficacious anthelmintic. Small intestine impactions are not seen when foals/weanlings are dewormed with fenbendazole, and therefore that is the drug of choice when deworming foals for the first time. During the first year of life, foals/weanlings should be dewormed a minimum of 4 times beginning at 2-3 months of age with fenbendazole. The second deworming should occur just prior to weaning, and the drug of choice will depend on whether primarily small strongyles or roundworms are seen on the fecal float. The third and fourth dewormings should be performed at 9 and 12 months respectively and they should target small strongyles (ivermectin or moxidectin).
In summary, small strongyles are the parasite of most concern for adult horses today. Having a fecal egg count done on your horse at least twice a year to determine his/her parasitic burden is essential. Deworming at least twice a year is recommended, with additional dewormings as needed based on the parasitic burden of the individual horse. Deworming in late fall or early winter with praziquantel (found in combination with ivermectin or moxidectin) is essential to treat for any tapeworm burden or bot infestation. Discussing your horse(s) with your veterinarian to develop an appropriate deworming strategy is the most important way to keep your horse(s) healthy.
Kristina McGinnis, DVM
New England Equine Medical and Surgical Center
AAEP Parasite Control Guidelines
Reading between the Lines: White Line Disease
What is it?
White line disease (WLD), is a multifactorial process that leads to a progressive separation of the inner zone of the hoof wall. The white line of the hoof can be visualized on the sole, and is the junction of the insensitive laminae of the hoof wall and the horn of the sole. The hoof wall consists of three layers: the stratum externum (external layer), stratum medium (middle layer), and stratum internum (inner layer). In WLD, the hoof wall separates from the underlying laminae (stratum internum) at the level of the stratum medium, also known as the tubular horn. When we use the term "white line disease", we are referring to the fact that the horse has some degree of separation of the hoof wall from its laminar attachments. Typically, the condition begins with a crack or opening within the white line, which then allows bacteria or fungus to enter the stratum medium. Since this is closely associated with the laminae, cavities subsequently develop between the laminae and outer hoof wall.
What causes it?
White line disease can affect a horse of any sex, age or breed, barefoot or shod. Mechanical stress, inappropriate farriery, genetic factors, and environmental conditions may all play a role in the development of WLD. Poor hoof hygiene has often been held responsible for the development of WLD, however it remains questionable as the initiating cause. It is believed that the primary event is mechanical stress on the inner hoof wall such as from poor hoof conformation or less than ideal farriery. These include, excessive toe length, poor hoof conformation, and various hoof capsule distortions such as long toe-under run heel, clubfoot, or sheared heels. This stress leads to breakdown of the hoof's natural barrier, and allows invasion of opportunistic bacteria that possess keratinolytic enzymes. These bacteria digest the hoof horn, leading to the progression of the separation proximally towards the coronet band. If left untreated WLD will become extensive and displacement of the distal phalanx can become a sequel.
How do we diagnose it?
Clinical signs for WLD can vary and the degree of lameness present can range from non-existent to severe. Some horses may show a positive reaction to hoof testers while others may not. This is why it is very important to start the diagnostic process with a thorough physical exam and lameness evaluation. As WLD becomes moderate to severe, damage is sufficient to allow mechanical loss of the attachment between the laminae and the inner hoof wall, clinical signs of pain (typically lameness) can be seen. When examining the foot from the solar surface, there is often a visual confirmation of a separation between the hoof wall and underlying laminae. Looking even deeper into the inner hoof wall, the inner white line will typically show a separation filled with a grey/white powdered horn material. A probe can be used to further explore the depth and extent of the cavitation. Additionally, a hollow sound is typically heard if the outer hoof wall is percussed with a hammer. WLD should be differentiated from other common foot lameness that will block out to a palmar digital block, such as chronic laminitis and foot abscesses. If lameness is present on initial evaluation, a thorough lameness examination should be performed including nerve blocks to confirm the suspected area followed by radiographs. When extensive hoof wall damage is present and subsequently pain, WLD can mimic laminitis both clinically and radiographically, and thus it is important to differentiate between the two.
Radiographs should be taken to show the extent of separation between the hoof wall as well as to rule out laminitis. A lateral and dorsopalmar view are generally sufficient to allow for accurate interpretation of WLD. In chronic cases of WLD, pedal osteitis has been seen as a sequelae. Radiographs also allow for better visualization of the hoof capsule and can help with trimming and shoeing the horse in the future.
How do we treat it?
When treating WLD, corrective trimming is imperative to remove abnormal stresses on the hoof wall, in conjunction with resection and debridement of the entire extent of the separated hoof wall until the firm, healthy adhesion of the hoof wall to the underlying stratum internum can be seen. Resection of the hoof wall is performed using hoof nippers, a hoof knife, and motorized tools.
Adjunctive shoeing techniques are then applied to provide adequate support to the remaining foot and to remove stress from the affected part of the foot. A heart bar or egg bar shoe redistributes weight-bearing forces to the frog and palmar region of the foot and away from those damaged and therefore weakened areas. Resilient putty is typically used in conjunction with shoe to provide distal phalanx support, especially if displacement of P3 (coffin bone) is a concern. Additionally, it is important that the hoof remains clean and dry. The horse must be kept in a dry stall after treatment, and drying agents (ie. iodine) can be applied to the resected area to prevent excessive moisture from building up. The affected hoof should be cleaned daily with a wire brush. Systemic medical therapy is not required in conjunction with the resection since this disease is limited to the keratinized area of the hoof wall. Plastic acrylic repair may be used as well for prosthetic hoof wall repair, as depicted in Figure 4.
Figure 4: Acrylic hoof wall repair
Prognosis is dependent on the response to treatment, as well as the effect of the original insult. Horses with poor hoof quality or primary laminitis tend to have reoccurrences of the disease. If initial response to treatment is good and proper environmental conditions exist, then the prognosis is better.
For any other questions associated with white line disease, please feel free to call New England Equine Medical & Surgical Center, or discuss management strategies with your local farrier.
Jordan E. Koivu, DVM
Elizabeth Taylor, DVM, DACVS - LA
"White Line Disease in Horses." Lameness in Horses: Merck Veterinary Manual. 1 Sept. 2015. Web. 10 Dec. 2015.
O'Grady, Stephen E. "Management of White Line Disease." Equine Podiatry. 2006. Web. 10 Dec. 2015.
Ross, Mike W., and Sue J. Dyson. "The Foot: Trauma to the Sole and Wall." Diagnosis and Management of Lameness in the Horse. 2nd ed. St. Louis, Mo.: Elsevier/Saunders, 2011. Print.
Recurrent Airway Obstruction (Heaves)
Horses are active and athletic animals that need to breathe efficiently and effectively to perform to their full potential. Respiratory problems can often go unnoticed, especially in the early stages, due to subtle or mild signs. The main signs of illness horse owners are advised to watch for such as fever, depression, or going off feed are not always present. Recurrent Airway Obstruction (RAO, "heaves") is a respiratory disease that is often overlooked in the early stages.
Recurrent airway obstruction is an allergic airway disease characterized by a chronic cough, nasal discharge, weight loss, and respiratory impairment that ranges from exercise intolerance to respiratory distress while at rest. Affected horses are typically middle-aged to older and do not show other signs of illness such as fever, depression, or pain. There have been two forms of RAO described: one is associated with exposure to irritants commonly encountered with confinement housing such as from dust, hay and bedding. The other is associated with molds growing on pastures in the summer. RAO is a common non-infectious inflammatory pulmonary disease that impacts the health and performance of horses across all equine disciplines.
Clinical signs occur in susceptible horses that are exposed to inhaled allergens from dust, mold spores and particles released by hay and bedding (straw bedding). When exposed to these allergens the horse's body responds by closing the airways (bronchoconstriction) and increasing bloodflow and cellular exudate resulting in inflammation and mucus production to trap the allergens and facilitate clearance. These mechanisms are meant to be protective of the airway but the result is detrimental to the horse's respiratory function. The bronchoconstriction and excess mucous increases the resistance to airflow especially during expiration. The increased expiratory pressure requires recruitment of the abdominal muscles to aid in exhalation. This results in well-developed abdominal muscles (hypertrophy of the external abdominal oblique muscle which gives the characteristic "heave line" appearance. The increased respiratory effort leads to decreased feed intake which results in weight loss. Horses with RAO tend to be exercise, heat, and humidity intolerant.
Continuous and prolonged irritation and inflammation of the airways increases their sensitivity resulting in exaggerated responses to the irritation, further exacerbating the problem. The respiratory tract's barrier defense is weakened and lead to secondary bacterial infections. Chronic infections lead to scarring of the lower airways further restricting the elasticity of the lung tissue and increasing the respiratory effort.
Recurrent airway obstruction is diagnosed based on clinical signs and by ruling out other causes of respiratory disease. A chronic cough, and nasal discharge without a fever are characteristic of RAO. An expiratory wheeze may be auscultated by your veterinarian on physical exam. Labwork typically shows a normal complete blood count, fibrinogen, and serum chemistry unless a secondary infection or concurrent disease is present. A Bronchoalveolar Lavage (BAL) is performed to evaluate cellular infiltrate, of which 35-50% of cells are expected to be neutrophils in horses with RAO. Spiral shaped mucous plugs from small airways (known as Curshmann's spirals) may also be seen. Transtracheal Wash (TTW) may be performed to obtain a sample for culture prior to a BAL in cases suspected of bacterial infection. Yellow exudate of increased viscosity may be visualized in the trachea via endoscopic exam. Radiographs may reveal over-expanded lung fields and peribronchial pattern of infiltrates while ruling out other lung disease (interstitial pneumonia, neoplasia, and abscess). Ultrasonographic evaluation of the lungs may also be used to assess the lungs and rule out concurrent disease.
Horses in respiratory distress need immediate veterinary intervention. Severe cases are treated with systemic corticosteroids and bronchodilators. While very effective, the potential complications (laminitis, adrenal suppression, decreased gastrointestinal motility, colic, etc) of these medications preclude their use as long-term therapies. Medical management with anti-inflammatories and inhaled bronchodilators are short term therapies to be used until the respiratory tract returns to a healthy state and environmental adjustments can be made.
The most important treatment and prevention of RAO is long-term environmental management. Affected horses should be kept on pasture at all times. A three sided run-in shelter may be provided for protection from inclement weather. Dry lots and enclosed confinement should be avoided. Prior to feeding, hay is to be closely inspected for signs of mold and soaked in water to remove dust and particulate allergens. Alternatively the horse's diet may be changed to a pelleted complete feed or fed bagged hay with high moisture content. Horses with the summer-pasture associated RAO respond best to stall confinement during the summer months when molds are growing on pastures. For horses that must be confined to a stall, stable management should be a priority. Hay should be stored in a separate building from where the horse is stabled, and never above the stall. Stalls should be well ventilated and cleaned daily, kept free of dust, cobwebs, and loose feed, and the horse should be removed during cleaning when the air concentration of particulate matter is highest. Additional measures such as using hypoallergenic bedding and watering arena footing can help to minimize dust and RAO irritation.
Early diagnosis and intervention is essential to prevent the disease from reaching an irreversible state. Recurrent airway obstruction is not curable, but it can be well managed through appropriate environmental changes. Horse owners and barn managers play an important role in the prevention and treatment of this disease.
Doctor Joslyn Mumford
Equine Colic: More than just a bellyache
It’s colic season!! Or so it seems that way in New England.
Colic, a term that simply means “abdominal pain”, is anything but simple when it comes to horses. Colic is one of the leading causes of premature death in horses and the number one emergency for equine veterinarians. Whether the clinical signs are obvious or very subtle, the sooner that you realize your horse is colicking, the better the prognosis will be.
Continue reading below for ten important things to remember when your horse is colicking on the farm as well as ways to decrease the risk of colic.
1) >Clinical signs of colic can vary immensely, depending on the horse, their pain tolerance, and the type of colic that they are experiencing. Some horses may exhibit multiple clinical signs, while others may only show one or two. Here are some clinical signs to watch out for that could mean your horse is colicking:>
- >Loss of appetite>
- >Flank watching (turning of the head to look at the abdomen)>
- >Biting at sides>
- >Straining to urinate>
- >Getting up and down repetitively>
- >Decreased fecal output or diarrhea>
- >Increased respiratory rate>
- >Increased or decreased gastrointestinal sounds>
2) >Check your horse’s vital signs. Try to get a heart rate or pulse rate, either by using a stethoscope to listen directly to the heart (just behind the elbow of the front left leg, under the shoulder) or get a pulse rate by feeling the facial artery underneath the horse’s jaw. A normal heart rate for most horses is between 28 and 44 beats per minute. If the heart rate is above 44 beats per minute, it is elevated and could be due to pain. Grab a thermometer and check to see if the horse has a fever – a normal rectal temperature should be between 99F and 101.5F. Take your horse’s respiratory rate, which should be between 12 and 20 breaths per minute. Check to see if there is any manure present in the horse’s stall or paddock, and if so is it normal consistency, dry or diarrhea.
3) >Call your veterinarian as soon as you are suspicious that your horse is colicking. Whether the clinical signs are severe or very subtle, waiting too long could allow small problems to become critical and critical problems to become untreatable. Describe your horse’s behavior to your veterinarian, and let them know the vital parameters if you were able to obtain them. It can also be beneficial to let your veterinarian know if the horse has a history of colic. Lastly, let them know if feces were present in the stall and if the horse has been eating and drinking normally. With this information, your veterinarian can better assess the horse over the phone as well as the severity of the colic.>
4) >While you are waiting for your vet to arrive, make sure your horse is not rolling, pacing or thrashing, as this can lead to further injury. Hand walk the horse if they continue to roll or thrash in a stall. If the horse will lie down quietly, without rolling or constantly getting up and down, this is okay. Sometimes, it is easier for gas to be passed when they are recumbent. Check on your horse every 15 minutes. Colics can progress rapidly in some circumstances and need to be closely monitored so that any deteriorating condition can be treated promptly.>
5) >Restrict access to any feed while you are waiting for your vet. Food can often make the existing problem worse, even though some horses still have an appetite when they colic. It is also important to limit any water intake until a veterinarian has passed a nasogastric tube to check for additional fluid (reflux) causing distension of the stomach. Excess water could lead to a ruptured stomach.>
6) >You should talk with your veterinarian over the phone before medicating the horse, since anti-inflammatories, analgesics and sedatives can mask clinical signs, which can make it more difficult for the veterinarian to properly diagnose the severity of the colic. If the horse is very painful and needs medication immediately before the vet can arrive, be careful not to overmedicate. Banamine® (flunixin meglumine) should only need to be given once every 12 to 24 hours. If banamine is not decreasing the horse’s level of pain, then the horse needs stronger pain medications and potentially medical or surgical treatment.>
7) >Whenever your horse is colicking, it is important to keep in mind whether the horse has the option of going to a referral center for further medical or surgical treatment. The sooner the horse is treated medically or surgically, the better the prognosis will generally be. Financial concerns play a huge role in this decision and so it is important to think about this before an emergency actually occurs. A medical colic that requires IV fluid therapy can cost up to $5000 and surgical colics can range from $5000 to over $15000 depending on complexity and postoperative complications. If you have an insurance plan, make sure you know beforehand how much your company will contribute.>
8) >Once you decide that the horse can no longer be medically managed at the farm and you would like to take it to a referral center, start to plan for transportation. Do you own a trailer or will you have to call a shipper? It is important to have a trailering plan in place before an emergency occurs so that time is not wasted trying to find a ride. If it is possible for the horse to be shipped in a box stall, or to remove the partition in a smaller trailer, this is best in case the horse goes down on the way to the referral center and becomes trapped between the divider. Never travel in the trailer with a colicking horse, as this can quickly become dangerous for the passenger. >
9) >Many colics occur due to changes in frequency of feeding, type of feed or hay, or decreased water intake. It is best to feed smaller amounts of feed more frequently throughout the day if this is possible. Any changes to your horse’s feed should be made very gradually over 10 to 14 days. Forage should always be the main component of a horse’s diet unless special circumstances discussed with your veterinarian state otherwise. Finally, always monitor your horse’s water intake and be sure to encourage them to drink as much as possible. This is especially helpful with preventing impactions. Whether this means adding some water to their grain, or putting out an extra water bucket with some electrolytes, it is important to take extra steps to ensure that they are staying hydrated.>
10) > Management strategies, such as effective deworming protocols, gastric ulcer prevention, and regular exercise all play a role in maintaining a healthy horse with a lower risk of colic. Always refrain from giving medications unless instructed by your veterinarian, since NSAIDs, such as Bute® (phenylbutazone) or Banamine® (flunixin meglumine), can cause gastric ulceration, and antibiotics can disrupt the natural microflora of the gut and predispose to colitis.>
Colic can be a scary condition when it happens to your horse, but taking steps to prevent it and being prepared to deal with it can certainly help everyone remain calm in the incidence that it does occur.
If you have any questions regarding this article, or the treatment and prevention of colic, please contact your veterinarian or the doctors at New England Equine Medical & Surgical Center.
Jordan E. Koivu, DVM
New England Equine Medical & Surgical Center, 15 Members way, Dover, NH 03820
My Horse has a Cough. Now What?
Lori Smolkovich, DVM
As a horse owner, it is often a clear decision as to whether your horse needs veterinary care. Examples include lameness, colic, choke, etc. But what do you do when your horse shows signs that are more vague, like a cough. It could be a mild irritation, or it could be indicative of an underlying condition that needs treatment. How do you decide? In this article, cough, some of the causes of cough, and treatment will be discussed. Hopefully this article will allow you as a horse owner to be able to make a more educated decision as to when a cough requires veterinary care, help you be prepared for some of the questions your veterinarian will ask you, and allow you to better understand why certain questions are being asked and why some tests are necessary to perform.
There are dozens of reasons why your horse could be coughing. So the best place to start is by determining whether or not your horse has a fever. Take your horse's temperature once or twice a day for several days. If the temperature is higher than 101.5 F your veterinarian should be contacted. A cough with a fever is often indicative of an infectious or neoplastic condition and warrants veterinary care immediately.
If your horse is not febrile, take notice of your horse's environment, times that he coughs, and whether he shows any other clinical signs. This will allow your veterinarian to have more insight as to what may be going on. Does your horse cough more in one season than the others? Does your horse cough when he is in his stall or outside in turnout? Does he cough when he is eating? During/after he has been exercised? Does he have nasal discharge? If so is it coming from one or both nostrils? Is the discharge clear, yellowish, bloody, etc?
The first thing your veterinarian will do to assess the cough, is a thorough physical exam. If an arrhythmia is ausculted (heard through a stethoscope), a cardiac ultrasound may be warranted. This is because if the heart is not able to adequately pump blood forward as a result of a heart condition, fluid can accumulate in the lungs, causing a cough. If respiratory noises can be ausculted in the lungs of your horse, a transtracheal wash (TTW) or a broncheoalveolar lavage (BAL) are warranted. These tests are different, and depending on what your veterinarian suspects is the problem, will decide which test is appropriate. A TTW is very useful for identifying infection such as a bacterial or viral pneumonia. A BAL is very useful if an infection is less likely and a condition such as Inflammatory Airway Disease (IAD), Recurrent Airway Obstruction (RAO) or pleural effusion is suspected. Both of these tests allow a sample of fluid to be collected. By analyzing the cells in the sample, your horse's condition can likely be diagnosed.
Ultrasound is a great modality to allow us to gather more information about the lungs. Even if no abnormal lung sounds can be ausculted, it is possible diseased lung is still present, it has just not progressed far enough for abnormal lung sounds to be detected. Thoracic ultrasound allows us to visualize the lungs and determine whether there is consolidation (deflated lung that is no longer able to participate in oxygen exchange), fluid in the lungs, pleuritis, pleuropneumonia, etc. Also, if there is fluid in the chest (pleural effusion), ultrasound allows us to choose the most accurate location for thoracocentesis (collection of lung fluid for analysis), which will in turn provide more information.
In working up and evaluating a horse with a cough, an endoscopy is warranted. During an endoscopy, a camera is used to visualize the trachea, upper airways and the guttural pouches. The endoscopy allows us to diagnose many conditions of the upper airway that can cause a cough. Examples include anatomic defects that result in the airway not being appropriately protected from debris, resulting in a cough, such as dorsal displacement of the soft palate, rostral placement of the palatopharyngeal arch, arytenoepiglottic fold entrapment, and subepiglottic cysts. Other conditions that can cause a cough, such as tracheal collapse, partial obstruction of the trachea, either by a foreign body or a mass can be visualized on endoscopy. Finally, the guttural pouches can also be inspected for conditions such as empyema (pus in the guttural pouches), chondroids, and guttural pouch mycosis (fungal infection in the guttural pouches).
Other clinical signs can help your veterinarian localize the problem, resulting in less tests and a quicker diagnosis. If nasal discharge is present with a cough, skull radiographs may be warranted because an infected sinus could cause discharge from the nose but also some of the discharge may travel down the throat causing a cough. If the cough only occurs during/after exercise, it is possible your horse has exercise induced pulmonary hemorrhage. In some cases, the blood runs down the throat and causes a cough. If the cough only occurs when your horse eats, conditions such as a cleft palate, dorsal displacement of the soft palate, and soft palate paresis should be ruled out.
Two of the more common causes of cough that owners often confuse are Recurrent Airway Obstruction (RAO), better known as heaves, and Inflammatory Airway Disease (IAD). RAO is a condition that generally affects older horses. These horses show increased respiratory effort at rest, exercise intolerance and a cough. It is frequently caused by an allergy, most often mold or dust. IAD is a condition that generally affects younger horses. Signs also include exercise intolerance and a cough, but IAD horses do not have increased respiratory effort at rest. IAD is also believed to have an allergic component. Treatment for both of these conditions consists of medical therapy and environmental changes. Initially the horse must be treated medically with anti-inflammatory medications and bronchodilators to allow the horse to breathe easier. But the environment of these horses must also be altered so that the inciting factor does not cause a recurrence of the condition. Environmental changes consist of removing the irritants from the horse's environment. This can include giving the horse a stall with a window or by the door to ensure good ventilation and fresh air, turning the horse out to reduce exposure to times when the barn has debris in the air, such as when the stalls are being mucked or when the aisle is being swept, not keeping hay stored above the horse's stall, using shavings that are not dusty, wetting the hay, keeping arena footing well watered to minimize dust, etc. All of these, are ways to manage the horse's environment so the condition will not reoccur.
A horse with a cough is a very vague complaint that many horse owner's have. It is also a frustrating condition for owner's because there are many possible causes so in turn, many tests may need to be performed by your veterinarian. By paying more attention to when and where the cough occurs, what your horse is doing at the time of the cough, and additional clinical signs that your horse may have, your veterinarian will be better equipped to find the cause and help your horse.
Polysaccharide Storage Myopathy (PSSM)
Dr. Cat Ruksznis
Let's face it: no one wants to go to work on Monday morning. In the days where 'horse power' really did refer to the draft horses pulling the cart, their drivers noticed that even the horses were reluctant to move on Mondays. In fact, this condition was dubbed "Monday Morning Disease" - horses were stiff and slow on Monday mornings after a weekend off while still on full feed. We know this disease by many different names today - tying up, rhadbomyolysis, azotemia, etc. Earlier observations to the contrary, this is a true disease of the muscles (mypoathy), not a coffee deficiency! Although horses may develop this disease sporadically, there are also horses with an underlying genetic predispositions. Polysaccharide Storage Myopathy (PSSM) is one such muscle disease.
What causes PSSM?
There are two types of PSSM: type 1, in which the specific genetic mutation has been identified, and type 2, a category which is essentially a catch-all for horses with PSSM that do not have the known mutation. As the name suggests, these horses have abnormal accumulation of a polysaccharide (a sugar) in their muscle cells. Type 1 PSSM is most common in horses descended from Continental European draft breeds (Quarter Horses, Warmbloods, Appaloosas) and has been found in over 20 breeds. These breeds have a mutation in the enzyme responsible for making glycogen (GYS1). Glycogen is a type of sugar which is normally stored in skeletal muscle fibers and used for energy during the first 20 minutes of exercise. In horses with PSSM, there is a greater amount of abnormally constructed glycogen created, which accumulates in the muscle cells. Although the link between abnormal glycogen and muscle cell damage has not been fully elucidated, we do know that the increased activity of the GYS1 enzyme disrupts the normal muscle metabolism during exercise, leading to muscle damage.
Horses with Type II PSSM do not display this mutation in GYSI, but the muscle cells do display abnormal glycogen deposits (mechanism unknown). It is possible that there are numerous, as of yet undetermined underlying causes that we are currently grouping under this heading.
What are the clinical signs?
Diagnosing muscle diseases can be tricky - they are easily confused with colic, acutely, or a lameness problem chronically. Acute clinical signs include sweating, muscle twitching, muscle stiffness, muscle fasciculations, dark colored urine, unwillingness to move and recumbency. Muscles are most often tense over the hind quarters and the signs worsen with continuing exercise. Although episodes are most often triggered by exercise, these signs are not always perfectly correlated.
As the muscle cells are damaged they release a substance known as myoglobin, which is normally contained within the cells. Myoglobin bears a passing resemblance to hemoglobin; the molecule found in red blood cells that allows them to carry oxygen. However, once myoglobin is free in the body it does more harm than good. The molecule accumulates in the kidneys and, in large enough quantities, can lead to renal failure.
Less severely affected horses with low-level chronic disease may show more subtle clinical signs. Poor performance, a bad attitude, lack of energy, slow onset muscle atrophy or unwillingness to track up may all be signs of PSSM.
How can you diagnose PSSM?
To first diagnose a horse with rhabdomyolysis (tying up), a biochemistry panel is very helpful. This test will show elevations in muscle enzymes (AST and CK) which increase with muscle damage. A chemistry panel will also allow your veterinarian to monitor kidney values, if the muscle damage is severe.
In the case that the patient is a breed known to carry the genetic mutation responsible to type I PSSM, genetic testing can be diagnostic. This requires a blood or hair sample to be sent away for testing. Type I or Type II PSSM can also be diagnosed through a muscle biopsy. A small sample of muscle can be examined with specific stains to look for abnormal cellular features and amylase resistant accumulations of glycogen.
What are the treatment options?
When working with a horse you suspect may be tying up, exercise should be stopped immediately. The horse should be offered water, but no other feed. Veterinary treatment of an acute case of rhabdomyolysis includes intravenous fluid therapy to flush the kidneys, muscle relaxants to stop muscle damage and anti-inflammatory/analgesic medication (NSAID's).
That being said, PSSM is primarily managed through exercise and dietary adjustments. After an episode, horses should be gradual brought back into consistent work with no prolonged period of rest. Regular exercise, being ridden or worked 3-4 days a week with access to daily turn out, is very important to horses with PSSM. Initially, exercise should be light (walk-trot) and they should always be warmed up adequately. Regular exercise is thought to improve energy metabolism within the muscle cells.
Horses with PSSM should be fed a diet low in nonstructural carbohydrates (starch/sugar), with a compensatory increase in fat if necessary to meet caloric requirements. There are many commercial options for low starch/high fat diets currently available. Restricting dietary sugars (NSC) from grass or hay is more difficult, but can be achieved though use of a grazing muzzle and/or soaking hay prior to feeding.
Even with excellent management, horses with PSSM will always be predisposed to developing muscle soreness. However, most will show improvement in clinical signs.