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  • Pigeon Fever

    Watch this video of a presentation on pigeon fever by Dr. Nora Grenager. (Be sure to turn up your sound!) Related resources you may also be interested in: “Pigeon Fever” by Nora Grenager, VMD, DACVIM and Tim Eastman, DVM, DACVS, MPVM AAEP Infectious Disease Guidelines: Pigeon Fever EDCC (Equine Disease Communication Center)

  • EGUS: Equine Gastric Ulcer Syndrome

    By Nora Grenager, VMD, DACVIM Equine gastric ulcer syndrome (EGUS) is prevalent in our equine population and can be a cause of a huge variety of clinical signs ranging from suboptimal performance and behavioral issues to poor appetite and mild colic. It has been estimated that 50 to 100 percent of adult horses have gastric ulcers depending on level of work and management practices. Unlike in humans, a horse’s stomach continuously secretes gastric acid because horses were designed to graze throughout the day. The equine stomach is divided into two parts — a smaller upper squamous portion (about one third) and a larger lower glandular portion (about two thirds) — separated by a raised border of tissue called the “margo plicatus.” The upper squamous portion is like a continuation of the esophagus; the lower glandular portion is where acid is produced. EGUS occurs when there is an imbalance between gastric acid secretion and the stomach’s normal protective mechanisms. Types of Gastric Ulcers There are two syndromes of EGUS that have different predisposing factors, signs, and treatments — gastric ulceration in the squamous portion and gastric ulceration in the glandular portion. The glandular portion of the stomach secretes acid and other compounds. It has intrinsic protective mechanisms to deal with acid and is accustomed to acid exposure. Ulceration in this portion is likely due to both an increased acid exposure as well as a decrease in its protective mechanisms. Gastric ulcers in the squamous portion is likely due to the fact that this region is not accustomed to, nor equipped for, acid exposure. The majority of gastric ulcers in the squamous portion of the stomach occur along the margo plicatus, which is closest to the glandular acid-producing portion. Risk Factors Factors that likely predispose horses to glandular ulceration include stress and administration of nonsteroidal anti-inflammatory drugs, called “NSAIDs,” such as phenylbutazone (Bute™), flunixin meglumine (Banamine™), and less commonly firocoxib (Equioxx™). Stress decreases the stomach’s natural protective mechanisms. NSAIDs also decrease the stomach’s natural protective mechanisms, more often with high doses or long duration of treatment. Factors that predispose horses to squamous ulceration include infrequent feedings, high concentrate diets, and intensive training. Stress and NSAID administration can augment these processes in this region as well. Feed deprivation or infrequent feeding has been found to cause gastric ulcers because when the stomach is small and contracted the squamous portion of the stomach is exposed to acid. The byproducts from fermentation of high concentrate diets can also cause acid injury of the squamous portion. Consuming hay and the salivation that accompanies eating (because saliva contains natural buffers) help to buffer stomach acid. Intense exercise potentially increases intra-abdominal pressure and delays gastric emptying time, which increases the exposure of the squamous portion to acid. Clinical Signs Many instances of gastric ulceration probably go unrecognized. Interestingly, the severity of a horse’s clinical signs does not correlate with the degree of gastric ulceration. Horses with EGUS may have poor or picky appetite, weight loss, rough hair coat, poor performance, poor body condition, sore back, “girthy” behavior, or changes in attitude (the horse may seem “grumpy”). A horse with EGUS can present with excessive teeth grinding or excessive salivation, mild recurrent colic or even a more severe acute colic episode, though this is uncommon. Diagnosis Suspicion of EGUS may be based on history and clinical signs, but evaluation of the stomach with an endoscope (a procedure called “gastroscopy”) is the only way to confirm the presence, type, and severity of EGUS. This procedure can be performed at the barn or at a referral veterinary facility. The procedure is usually done in the morning after an overnight fast (the horse must be fasted for a minimum of 12 hours prior to gastroscopy so that the stomach is empty for evaluation). The horse is typically sedated and the endoscope is passed through the nostril down the esophagus into the stomach. The presence, severity, chronicity, and type of gastric ulceration is determined. Unfortunately, there is no blood or fecal test available that can accurately diagnose EGUS. Treatment Several types of drugs are available and commonly used to treat EGUS, and it depends on whether ulceration is present in the squamous, glandular, or both parts of the stomach. Treatment duration usually lasts 4–8 weeks. The gold standard treatment for squamous ulceration is omeprazole (Gastrogard™), a proton-pump inhibitor drug that directly blocks acid secretion. It is formulated as a flavored oral paste given once daily and has been proven to most effectively cure gastric ulceration. Ideally this is given on an empty stomach, 30–60 minutes prior to feeding (so usually first thing in the morning or just before lunch). Antacids (such as aluminum or magnesium hydroxide and calcium carbonate) can help relieve immediate clinical signs, but do not effectively treat the ulceration. Antacids also have a short duration of effect and need to be administered orally every 2–3 hours so they are not convenient for long-term treatment. The typical treatments for glandular gastric ulceration include sucralfate and misoprostol, sometimes along with Gastrogard™. Sucralfate coats ulcerated areas and stimulates the GI tract’s own local protective mechanisms. It is sometimes used alone, or in conjunction with Gastrogard™ for mild to moderate cases of glandular ulceration. Misoprostol is used for moderate to severe glandular ulceration (usually in conjunction with sucralfate +/- Gastrogard™). It increases the body’s own protective mechanisms against glandular ulceration. It cannot be used in pregnant mares and it can occasionally cause transient cramping at the start of administration. Therapy is typically tapered off rather than stopped cold turkey. We usually recommend repeat gastroscopy at the end of the treatment interval to assess the response to treatment. Most cases of squamous ulceration respond well to appropriate treatment, but glandular ulceration is less predictable. Some cases respond well to one month of treatment, while others require longer; unfortunately, it is difficult to predict into which category a horse will fall. Last but certainly not least, it is widely believed that EGUS does not occur in a vacuum. There is typically something else driving the condition — be it musculoskeletal pain, other GI pain, stress, or feed changes. It is very important to try to home in on any other potential causes to maximize the efficacy of your treatment and prevent recurrence. Prevention Gastrogard™ given at a quarter dose once daily (called Ulcergard™ — available over the counter) is effective at preventing the formation of gastric ulcers. This is often recommended around times of stress or NSAID administration in horses at risk for EGUS. Corn oil added to the feed has also been shown to help increase gastric pH (i.e., decrease the amount of acid), although some horses can become “hot” with corn oil supplementation. It has been shown that supplements containing pectin and lecithin can help prevent EGUS, and mineral-rich calcified marine algae helps prevent squamous ulceration. Most importantly, prevention of EGUS involves recognition of situations that may predispose a horse to gastric ulceration. Horses on high doses of NSAIDs or long-term treatment with NSAIDs are theoretically at higher risk for EGUS. Horses in training or who are fed high concentrate meals without access to roughage are at an increased risk. Performance horses are not the only horses at risk for EGUS, as severe ulceration has been diagnosed in recreational and retired horses in seemingly calm environments. It is important to keep EGUS in mind if a horse is being exposed to potential stresses, particularly those horses that have had EGUS in the past. Recognition of clinical signs with appropriate diagnosis and treatment of EGUS improves attitude, performance, and quality of life for our horses.

  • Emergency & Disaster Preparedness

    Published by the American Association of Equine Practitioners (AAEP) When an emergency or natural disaster occurs, it is always in the best interest of the horses for both the equine practitioner and the horse owner to be prepared. Foreign animal disease outbreaks or other catastrophic events can adversely affect the health and well-being of horses. Preparation is a key part of making sure your horses are safe and taken care of in a crisis situation. One must understand who the other resources are and what their plan is in order for a coordinated response to result. The American Association of Equine Practitioners (AAEP) has collected helpful links to make sure you, the horse owner, have vital information available before a disaster strikes. Learn more...

  • EDCC: Disease Outbreak Alerts

    The Equine Disease Communication Center (EDCC) is an industry-driven initiative which works to protect horses and the horse industry from the threat of infectious diseases in North America. The communication system is designed to seek and report real time information about diseases similar to how the Centers for Disease Control and Prevention (CDC) alerts the human population about diseases in people.

  • AAEP Horse Owner Resources

    The American Association of Equine Practitioners (AAEP) provides a wealth of information and resources for horse owners on horse health, how to find equine veterinarians and dental practitioners, disaster preparedness, disease outbreaks, and much more. “To protect the health and welfare of the horse” is one of the AAEP’s most important pursuits. The association and its members provide direct benevolent assistance to horses and charitable groups, including rescue and retirement facilities, international aid projects and emergency relief during natural disasters. Key industry initiatives, such as the Unwanted Horse Coalition and the Racing Medication & Testing Consortium, were formed from the AAEP’s sponsorship and commitment to equine welfare and practices in the best interest of the horse. .

  • Bone Scans: Using Nuclear Scintigraphy to Uncover Lameness

    Watch this video of a presentation on nuclear scintigraphy by Dr. Jacquelyn Dietrich. (Be sure to turn up your sound!) Learn more about Nuclear Scintigraphy at Steinbeck Peninsula Equine Clinic...

  • Equine Colic: Risk Factors, Disease Process and Prevention

    Watch this video of a presentation on equine colic by Dr. Danica Wolkowski. (Be sure to turn up your sound!) Related resources you may also be interested in: “Equine Colic: What to Expect,” by Nora Grenager, VMD “Enteroliths: A Rock and a Hard Place,” by Timothy G. Eastman, DVM, DACVS, MPVM “Colic in Horses: What You Should Know,” by Timothy G. Eastman, DVM, DACVS, MPVM “Colic Questions Answered,” by Lindsay Berreth, published in Chronicle of the Horse “Colic Updates and Prevention,” by Dr. Nancy Loving, published by American Association of Equine Practitioners (AAEP) “Colic: Minimizing Its Incidence and Impact in Your Horse,” published by American Association of Equine Practitioners (AAEP)

  • Maximizing the Golden Years: Care for the Aging Horse

    Watch this video of a presentation on equine geriatrics by Dr. Amanda Hedges and Dr. Nora Grenager. (Be sure to turn up your sound!) Related resources you may also be interested in: “Options for Managing Osteoarthritis” by Dr. Amanda Hedges “Choosing Oral Joint Supplements" “End-of-Life Considerations” by Dr. Amanda Hedges

  • Options for Managing Osteoarthritis

    By Amanda Hedges, DVM, cVA, CVSMT What is Osteoarthritis? A healthy joint relies on the production of synovial (joint) fluid to lubricate structures, bring in nutrients and clear away cellular waste products, and to transmit forces through the leg. Healthy synovial fluid is produced by cells in the cartilage in response to movement. Some components of healthy joint fluid include hyaluronic acid (HA) and polyglycosaminoglycans (PGAGs). Inflammation due to an acute traumatic event, chronic low-grade trauma/wear and tear, or a joint infection impedes the production of healthy joint fluid. Specifically, pro-inflammatory molecules damage cartilage. In general, inflammation leads to pain, as the joint loses its ability to lubricate, bring in nutrients and remove waste, and transmit force. In response to this pain and instability, the body attempts to stabilize the joint, remodeling it to limit mobility. The joint capsule becomes thickened and bone proliferates around the joint in an attempt to immobilize the damaged area. What are the Signs of Osteoarthritis and How Do We Diagnose It? In its advanced stages, signs of arthritis are hard to miss. These include clear lameness and/or visible joint distortion by extensive bone proliferation. However, signs can start subtly and the horse may be able to compensate, depending on the level of performance. These milder signs may include uneven wear on the hoof/shoe, difficulty holding up a limb for the farrier, decreased performance abilities, difficulty standing square, difficulty laying down or getting up, or behavioral changes. When dealing with an infected joint, joint fluid is sampled and analyzed for markers of inflammation. If arthritis is secondary to “wear and tear,” diagnostic imaging (radiographs, ultrasound, CT) is the best way to confirm the diagnosis. Diagnostic nerve blocks may be used during workup to both hone in on a particular joint and to shed light on the clinical significance of the changes seen on imaging. Treatment Goals There are three objectives of treatment: 1) decrease inflammation, 2) prevent further damage, 3) relieve pain. It is immensely important to remember that there is no one-size-fits-all program for treating arthritis. If there was, everyone would do it and we wouldn’t have so many options! It is always critical to work with your veterinarian to determine the best plan based on your goals for your horse; making sure to discuss reasonable expectations for treatment and possible costs. Oral Supplements Oral supplements rely on research in horses and other species to make claims for effectiveness. Challenges of oral supplements include lack of FDA-regulated supply, mixed results from evidence-based-research, widespread anecdotal claims, and palatability. Oral supplements can be beneficial in that they can be less expensive than some treatments and are relatively easy to administer. It is important to weigh out the cost vs. possible benefit as compared to injectable joint therapies long-term. Learn more about assessing oral joint health supplements... Topical Therapies Diclofenac (Surpass®) is an anti-inflammatory drug formulated to penetrate the skin and provide local anti-inflammatory actions and pain relief. This drug is in the same class as oral non-steroidal anti-inflammatory drugs, so care should be used to minimize negative systemic side effects when both topical and oral products are used together. Occasionally a skin reaction can be seen, and owners should wear gloves when applying this product. Many other topical options are available on the market or through your veterinarian. As with any product, discuss the benefits and possible risks with your veterinarian. Oral Medications The staple of anti-inflammatory drugs in horses is a class of drugs called non-steroidal antiinflammatory drugs (NSAIDs). Most commonly used are phenylbutazone (Bute®), flunixin meglamine (Banamine®), firocoxib (Equioxx®), and naproxen. These drugs act by halting the systemic inflammatory cascade at different points. Unfortunately, non-specific blocking of the cascade can also decrease other necessary pathways, resulting in the risk of damage to the stomach in the form of gastric ulcers, risk of damage to the intestinal lining resulting in colitis, and risk of kidney disease. Equioxx® is the most pathway-specific option and is often preferable for prolonged use (up to two weeks) but still carries some degree of risk. Oral steroids can also decrease systemic inflammation. Unwanted side effects of prolonged steroid use in horses include immune suppression and laminitis. Injectable Options Legend® and Adequan® are injectable joint support supplements both labeled for the prevention and treatment of arthritis. They may provide systemic anti-inflammatory effects. No contraindications are listed for either drug, but the risk of a site reaction applies, as with any intramuscular injection or intravenous injection. Legend® is a synthetic hyaluronic acid (HA) that has been studied to treat carpal and fetlock arthritis secondary to non-infectious causes. It can also be used in the joint for local anti-inflammatory therapy. It can be used as a weekly intravenous injection for 3 weeks, monthly, or at your veterinarian’s discretion. Adequan® is a synthetic polyglycosaminoglycan (PGAG) that has been studied to treat carpal and hock arthritis secondary to non-infectious causes. It is injected into the muscle every 4 days for a total of 7 injections, or at your veterinarian’s discretion. Note that both of these products were studied in young adult healthy horses, and their effect on a horse outside of this age-range is only anecdotal. However, both are widely used in veterinary medicine. Similar to oral steroids, long-acting injectable steroids may improve your horse’s comfort. Most common is a long-acting steroid that can provide systemic anti-inflammatory relief. Notable risks include site-reaction, immune-suppression, and risk of laminitis. Joint Fusion The body’s goal with producing excess bone around the joint is to decrease motion in the joint. In some cases, such as pastern or hock arthritis, we can help the body achieve this goal by fusing the joint (aka arthrodesis). Fusion can be hastened by injecting the joint with chemical irritants. Surgical procedures can also hasten joint fusion. Screws, plates, and/or cartilage drilling can all be employed to immobilize the joint. While these options may involve a greater initial cost, the chance of long-term comfort may make joint fusion a good choice for your horse. Intra-articular Options Anti-inflammatory drugs, synthetic joint components, and biologically derived anti-inflammatory products can all be injected directly into an arthritic joint to improve comfort. Steroids such as betamethasone and triamcinolone, often in conjunction with synthetic joint fluid components such as hyaluronic acid, can be injected under standing sedation and can provide targeted relief. Methylprednisolone acetate may decrease inflammation and impair cartilage health, making it a good potential choice for joints that are easy to fuse (such as the hock joints or pastern joints). Polyacrylamide gel (PAAG) is a synthetic gel that can be injected into a joint to add physical stability to a joint, although more research is needed before equine use can be recommended. Regenerative medicines such as interleukin-1 receptor antagonist protein (IRAP), Prostride®, stem cells, and platelet-rich plasma (PRP) may decrease inflammation and improve comfort in an arthritic joint as well. Anti-inflammatory mediators are removed and processed from the horse’s own blood, bone marrow, or fat tissue (depending on which therapy), and injected into the joint. This option may be preferable in a patient for whom steroids are not a good choice or depending on the nature of the injury. Learn more about these regenerative medicine modalities... Risk of joint infection or joint flare is present anytime a joint is injected. These risks are decreased by the use of sedation to prevent mobility and sterile injection technique. Dose and frequency of treatment depends on response to treatment. Adjunctive Therapies Acupuncture, chiropractic medicine, massage, light/laser therapy (usually Class 2 or 3), pulsed electromagnetic field (PEMF) therapy, thermal therapy, vibration floor plates, and controlled exercise programs may also improve comfort. Acupuncture creates a systemic release of endorphins and improves blood flow to painful areas. Chiropractic medicine relies on a high-velocity, low-amplitude thrust to a restricted joint (usually in the spine) to theoretically improve blood flow and nerve function. Massage can improve circulation and interrupt pain receptors. Light/laser therapy transmits energy in the form of light to cells, stimulating healing and pain relief. PEMF therapy (Assisi Loop®) pulses energy to cells via an electromagnetic current to stimulate healing and pain relief. The vibration floor plate VitaFloor® has been shown to improve topline muscle mass and improve circulation throughout the body. Learn more about equine acupuncture and chiropractic medicine... Controlled Exercise Perhaps the tool that has the greatest potential benefit and least cost is controlled exercise. A regular low-impact exercise program, such as walking for 20 minutes daily, can improve joint health and mitigate the potential injury and inflammation that comes from weak postural muscles and stiff joints. Exercises that focus on postural strength and core stability, low-impact mobilization of joints, and mental stimulation can benefit the arthritic patient. Equine rehabilitation facilities offer exercise programs, hydro-treadmills, and swimming pools to achieve equine fitness goals. Talk to your vet for more details! Other resources to consider: “Equine Joint Therapies: What to Know” by Erica Larson, published by The Horse “Lameness & Joint Medications” by Benjamin Espy, DVM, DACT and Justin Harper, DVM, MS, DACVS, LA, published by the American Association of Equine Practitioners (AAEP) “Equine Osteoarthritis: Early Interventions” by Natalie DeFee Mendik, MA, published by The Horse “What You Need to Know about Equine Osteoarthritis” by Stacey Oke, DVM, MSc, published by The Horse “Alternatives for Managing Osteoarthritis in Horses: PAAG and Stanolozol” by Alexandra Beckstett, published by The Horse 10 Equine Osteoarthritis Resources on

  • Choosing Oral Joint Supplements: ACCLAIM System

    Oral joint health supplements (OJHSs) “are a group of nutritional supplements that contain one or more non-nutrient, non-drug ingredient,” according to John P. Caron, DVM, MVSc, Dipl. ACVS, a professor in the Department of Large Animal Clinical Sciences at Michigan State University. With scores of OJHSs on the market, it can be difficult for horse owners to decide which one to try. Below you'll find an outline of the seven-step “ACCLAIM” approach to assessing OJHSs — for more details, see “Oral Joint Supplements for Horses” by Stacey Oke, DVM, MSc, published by The Horse. Below is a list of some common OJHS ingredients and what they may do to benefit horses, with dosage recommendations from the American Association of Equine Practitioners (AAEP). Note that combination products seem to have the best results. Steinbeck Peninsula Equine Clinics veterinarian, Amanda Hedges, reminds us that “Oral supplements rely on research in horses and other species to make claims for effectiveness. Challenges of oral supplements include lack of FDA-regulated supply, mixed results from evidence-based-research, widespread anecdotal claims, and palatability. Oral supplements may be beneficial in that they can be less expensive than some treatments and are relatively easy to administer. It is important to weigh out the cost vs. possible benefit as compared to other therapies, in the long-term.” For more information, see “Options for Managing Osteoarthritis” by Dr. Amanda Hedges.

  • End-of-Life Considerations

    By Amanda Hedges, DVM, cVA, CVSMT “Is it inhumane to keep him alive? What would YOU do in this situation?” Making end-of-life decisions can be difficult and emotional. Veterinary medicine and preventative care means horses often survive conditions that would result in death in the wild. By providing quality care, we also prolong our horse’s natural life expectancy. For example, most housing situations lack predators that would eat a horse that cannot keep up with the herd. We provide our horses with regular access to feed and water so they do not starve or suffer from dehydration as their feral counterparts may. By taking a horse out of its “natural” environment, we also accept the responsibility of providing a humane end for our horses. Our hope is that the following considerations will help you navigate this situation and prepare, as best as possible, for when the time comes to facilitate a peaceful passing. Ambulation Can your horse lie down safely, and does he/she lie down regularly (at least once every 2-3 days)? Does he/she lie down so much that he has bed sores/pressure sores? Can your horse walk around? Does he/she safely and voluntarily walk around his/her enclosure? If your horse lives in pasture, can he/she keep up with the herd? Can your horse perform basic behaviors, such as picking up and holding all 4 feet for the farrier? Appetite Does your horse show interest in feed? Is he/she able to chew and swallow the feed you provide? Are you able to make any feed changes your horse may need? Are you able to medicate your horse as frequently as he/she may need? Is it safe for your horse to receive preventative dental care? Attitude What are your horse’s three favorite things? Can he/she still do them safely, and as regularly, as he/she would like? Does your horse have something that he/she looks forward to (besides eating) every day? Is your horse in pain? Refer to the Pain Scale developed by Colorado State University to better answer this question. Can your horse’s pain be managed? Consider writing down your horse’s behaviors in a notebook at each visit to look for changes over time. Consult with people you trust who know you and your horse. Has your trainer/farrier/barn friend noticed a difference in your horse’s attitude? Miscellaneous Can your horse’s condition(s) be cured? If they cannot be cured, can they be managed adequately? Can you afford the costs of medications, procedures, and/or recheck visits needed to manage the situation? Do the good days outweigh the bad? If there are more bad days than good, quality of life questions prevail. Emergencies: know as best as possible what you are able and willing to do for your aged horse. While it can be difficult and emotional to think about end-of-life decisions, it is far preferable to have considered how you will handle an emergency situation before it arises. It is much more challenging to have a clear and rational thought process during a veterinary crisis. Are you aware of the cost and process of euthanasia? How will the remains be handled? Be realistic with yourself and your situation. Honestly answer the question “What does my horse want?” with the knowledge that your emotions may make this question difficult to answer. And as always, discuss any questions or concerns that arise with your veterinarian. Except under extreme emergency exceptions, your veterinarian cannot make this decision for you. All he or she can do is do his/her best to answer your questions and support your decision. The veterinarian may be more or less involved in helping you make this decision depending on the relationship you have developed. This is also a good article about end-of-life considerations: “Being Prepared for Equine Euthanasia" by Holly Mason, MS, DVM, published in The Horse.

  • Deworming Programs – One Size Does Not Fit All

    Gastrointestinal Parasites in Adult Horses By Nora Grenager, VMD, DACVIM Over the past ten to fifteen years, there has been a huge shift in the equine veterinary community’s thoughts on parasite prevention. It is difficult to pick up a horse magazine or browse an equine website these days without reading about parasite resistance. Resistance to dewormers is increasing throughout the world, which is particularly concerning given the lack of new types of dewormers available. While there are many brand names, there are really only three or four main types of dewormer drugs. Unfortunately diatomaceous earth is ineffective in killing gastrointestinal parasites in horses. Parasitologists say it is not a matter of when, but rather how rapidly, parasite resistance will develop in any given region. The silver lining of this impending resistance is that we are now focusing our attention on more strategic deworming programs, rather than rigid regimens that do not take into account an individual horse’s needs. Most horses do not need to be dewormed as frequently as previously thought. It makes much more sense, from both a horse and herd perspective, to tailor the deworming program to each horse. Why do we deworm at all? Horses have evolved with parasites over millions of years and it is okay for a horse to have some parasites; actually it probably keeps their immune system active. Our goal of deworming programs is not to completely eliminate parasites. While often small worm burdens (i.e., just a few worms) cause no clinical signs, when there is a large burden these parasites steal nutrition from the horse. Gastrointestinal parasites can cause weight loss or poor growth, rough hair coat, poor performance, tail rubbing, colic, diarrhea, and decreased ability to fight other infections or respond to treatment for illness. The main gastrointestinal parasites of concern in adult horses (over 18 months of age) include: small strongyles, large strongyles, tapeworms, bots, and pinworms. This article will focus on adult horses, as younger horses have deworming needs that are distinct from those of adult horses. Each type of parasite has its own life cycle, but there are some similarities among them. Generally speaking, grazing horses ingest parasitic larvae that then (sometimes after extensive migration or hibernation that can cause significant damage) develop into adult worms within the gastrointestinal tract. These adult worms reproduce and the horses pass eggs in the manure so the cycle can begin again. Pasture conditions, environmental temperature and humidity all affect how long this takes and parasites in our part of California typically prefer late winter/early spring conditions when it is wet and getting warmer. There are three main types of large strongyles: Strongylus vulgaris, Strongylus edentatus, and Strongylus equinus. These large strongyles, also called “blood worms,” used to be the primary targets of deworming programs, but for the most part have been well-eradicated by the frequent deworming protocols used for the last several decades. Large strongyle larvae penetrate the lining of the small intestine and migrate throughout the body along blood vessels, causing hemorrhage and inflammation in the liver, pancreas, or abdomen before eventually taking up residence and reproducing in the large intestine. The migration of these large strongyles can cause organ damage or blood vessel damage with subsequent intestinal infarction and necrosis, peritonitis, and severe colic signs; the only way to diagnose this condition is at surgery or after death. There are over forty different species of the small strongyles or cyathostomes. Small strongyle larvae invade the large intestine and encyst (form a capsule in the intestinal wall), where they can safely hibernate for up to 2.5 years, a process called “arrested development,” until it is time to mature and then emerge. The larvae will often remain encysted during the hot, dry summer months or cold winter months during which they would have a difficult time surviving on the pasture. They are able to detect when environmental conditions will be favorable for their propagation and emerge at that time. When they emerge they can cause a large amount of inflammation within the intestinal wall, causing diarrhea of variable severity or colic. Diagnosis of large or small strongyle infections is dependent on finding the eggs in manure. However, during migration or arrested development there may be few to no eggs in the manure because it is larvae, not egg-producing adults, that are present. Tapeworms, or Anoplocephala perfoliata, have a more complicated indirect life cycle involving an intermediate host. Some larval stages of the tapeworm’s development take place in oribatid mites, which are prevalent on many pastures. Horses are infected by eating the tiny infected mites while grazing. Once ingested, the tapeworms attach to the intestinal lining, preferentially at the ileocecal valve between the small and large intestine, and complete their life cycle there. This can cause colic due to spasm of the intestine, blockage of the intestine, or telescoping of the intestine at the ileocecal valve (called “intussusception”). Diagnosis is based on finding eggs on fecal examination (which is not very sensitive) or serum antibody testing (which is difficult to interpret). Tapeworms, or Anoplocephala perfoliata, have a more complicated indirect life cycle involving an intermediate host. Some larval stages of the tapeworm’s development take place in oribatid mites, which are prevalent on many pastures. Horses are infected by eating the tiny infected mites while grazing. Once ingested, the tapeworms attach to the region between the small and large intestine (the ileocecal valve) and complete their life cycle there. This causes inflammation at the site, with signs of colic due to spasm of the intestine, blockage of the intestine, or abnormal motility with telescoping of the intestine at the ileocecal valve (called an “intussusception”). Diagnosis is based on finding eggs on fecal examination (which is not very sensitive) or serum antibody testing (which has not yet been well validated). There are two main types of horse botflies: Gasterophilus nasalis and Gasterophilus intestinalis. The adult botflies lay eggs in a horse’s hair coat that the horse then ingests during routine grooming. The eggs develop into larvae as they migrate to the stomach, then attach to the horse’s stomach where they can cause gastric ulceration or colic. While these are very common, they rarely cause notable clinical signs. Pinworms, or Oxyuris equi, can live in the large intestine and small colon and cause colic or anal pruritis (an itchy hind end as evidenced by tail-rubbing). Most often these infections are not diagnosed on a fecal sample. Instead, a piece of tape is used to collect and then identify eggs from around the anus. One of the most important concepts about parasite control is that each horse has inherent (likely at least partially genetic) variable susceptibility to gastrointestinal parasites. It is said that 20% of horses shed most of the parasite eggs, and 80% of horses shed very few eggs. Therefore most horses do not need to be dewormed very frequently, while only a few horses need to be dewormed more often. This difference in an individual horse’s susceptibility to parasites underscores the fact that if we use one deworming protocol for all horses, we are deworming some horses too often and other horses not often enough. Therefore, it would be ideal to only deworm horses that have too many parasites. So how do we determine which horses have too many parasites? Currently, our best option is the fecal egg count (FEC), which is relatively inexpensive and easy to perform but unfortunately this method of detecting parasite numbers is not very sensitive. The procedure involves floating a manure sample and counting the number of eggs seen. Horses are then categorized as non-shedders (no eggs seen), low shedders (usually less than 150 eggs per gram), moderate shedders (usually 150-500 eggs per gram), or high shedders (usually greater than 500 eggs per gram). In adult horses, this technique mostly counts large or small strongyle eggs, and sometimes tapeworm eggs. This is the most reliable method we have to noninvasively determine parasite burdens, but it has several limitations. First, as discussed above, it is often the larval stage of the parasite that causes a problem, and larvae are not sexually mature and therefore not making eggs. Second, the number of eggs does not always correlate very well with the number of adult parasites. Third, if the sample is too old or sits too long before evaluation, the egg counts can be falsely low AND there can be variation in the amount of eggs passed between piles of manure. There are blood tests available to help diagnose tapeworm infections, but the results are difficult to interpret because the test does not distinguish well between active and previous infection so it is not particularly helpful in diagnosing tapeworms in a single horse (better at telling if there is an issue within a herd). So while the FEC is not very sensitive, it is the best test routinely available to us to determine a horse’s parasite burden. There’s a cool new smartphone app that should be available soon to do FECs stall-side for less cost and faster results. How do we determine each horse’s individual susceptibility to parasites? Our methods of detecting parasite numbers are unfortunately not very sensitive. Fecal egg counts (FEC) are most often used and are relatively inexpensive, certainly noninvasive, and are easy to perform. The procedure involves floating a manure sample and counting the number of eggs seen. Horses are then categorized as non-shedders (no eggs seen), low shedders (usually less than 200 eggs per gram), moderate shedders (usually 200-500 eggs per gram), or high shedders (usually greater than 500 eggs per gram). In adult horses, this technique mostly counts large or small strongyle eggs, and sometimes tapeworm eggs. This is the most reliable method we have to noninvasively determine parasite burdens, but it has several limitations. First, as discussed above, it is often the larval stage of the parasite that causes a problem, and larvae are not sexually mature and therefore not making eggs. Second, the number of eggs does not always correlate very well with the number of adult parasites. Third, if the sample is too old or sits too long before evaluation, the egg counts can be falsely low. There are blood tests available to help diagnose tapeworm infections, but the results are difficult to interpret because the test does not distinguish well between active and previous infection. So while the fecal egg count is not very sensitive, it is the best test routinely available to us to determine a horse’s parasite burden. Parasitologists and veterinarians have done extensive work to make it as useful as possible in creating an evidence-based parasite control program. The good news is that research has shown that if a FEC is performed long enough after the last dewormer was administered so that no more dewormer is present in the horse’s system (i.e., 4–5 weeks for pyrantel/fenbendazole/oxibendazole, 6–8 weeks for ivermectin, and 10–12 weeks for moxidectin) then the results stay consistent over time. Once a horse has shown itself to be a non- or low-shedder, this will remain true unless something change’s significantly in the horse’s health (such as the horse developing equine Cushing’s syndrome or recovering from serious systemic disease). Therefore, after one or two negative or low-shedder FEC, horses in these categories no longer need to have FEC performed unless there are suspicious clinical signs or something changes in their condition. This ideal single sample would also be taken in the late winter/early spring here in CA, when pastures are wet, because parasites here do not enjoy the hot, dry summers. The ideal deworming program then would focus on each individual horse’s parasite susceptibility and would determine if there is any parasite resistance to dewormers on a farm/facility. Resistance to dewormers can be determined by performing the Fecal Egg Count Reduction Test (FECRT). The FECRT involves doing a pre-treatment fecal egg count, administering a dewormer if the horse is a moderate or high shedder, and then rechecking the fecal egg count on those horses that were dewormed in 10–14 days. This provides information as to whether the horse is a low, moderate, or high shedder of eggs, and then also provides information as to whether the dewormer administered is efficacious. Once resistance to a dewormer has been documented at a facility, that resistance will remain. To slow the spread of resistance to dewormers, some parasites need to be kept “in refugia.” These parasite are those that are not exposed to a dewormer at the time of treatment, either because they are encysted, on the pasture, or in horses not dewormed. So, if non- or low-shedder horses are dewormed less frequently, they would then likely shed some eggs (of parasites that have not been exposed to dewormer) into the environment, thus diluting out any possibly resistant parasites. Parasites in refugia are not under selection pressure to develop resistance, and therefore are maintained as a relatively “resistance-free” population.This concept of keeping some parasites around that have not ever been exposed to dewormer is key in the prevention of resistance. Additional strategies should be considered to help minimize parasite exposure. Larvae can live for weeks in a pile of manure, and are easily disseminated when the manure gets spread out, thus increasing pasture contamination. For this reason it is also important not to drag or harrow a pasture while horses are grazing on it. It is important to not put horses on a pasture for 2–3 weeks after harrowing, and pastures should never been harrowed in the winter or wet months. Manure should also only be spread on a pasture if it’s been appropriately composted first to kill parasites. Daily manure removal from pastures may be easier said than done, but is the most effective way to prevent pasture contamination. Horses who live in stalls or dry paddocks are therefore at lower risk for parasite exposure. Manure should not be spread in a pasture unless it has been composted for at least two weeks, or unless the pasture will be ungrazed for at least two weeks in the hot, dry summer. Sharing pastures with livestock (cattle, sheep, goats, camelids) is another highly effective way to minimize parasite contamination, but this is not often practical. Lastly, using feeders in pastures/paddocks so horses are not eating off the ground and ingesting parasites (also good for sand control!). In Denmark dewormers can only be purchased from veterinarians, and are only prescribed if a horse has evidence of a significant parasitic infection. This was implemented in 1996 and is the most dramatic example of developing a dewormer program with your veterinarian’s advice. As we are slowly starting to incorporate more of these ideas into deworming practices here in the United States, each owner and veterinarian will need to work together to determine what is the best program for his/her horse. Some may opt to only deworm those horses with higher egg counts, some may opt to use a particular dewormer once or twice a year to kill any migrating large strongyles, then the rest of the year only deworm those horses with higher egg counts. The FECRT should be performed as needed to evaluate for any emerging resistance. Regardless of the program chosen, it is clear that the time has come to think differently about deworming. If we do not, the resistant parasites will eventually force our hand as resistance is being documented with increasing frequency around the country and world. In general, at Steinbeck Peninsula Equine Clinics we still recommend twice yearly deworming at the time of spring/fall vaccines. In the fall we usually recommend ivermectin or pyrantel or fenbendazole, while in the spring we recommend using a product that will kill tapeworms such as Quest Plus, Zimectrin Gold, or Equimax Plus. Each horse should have a FEC done at least once, ideally in the spring and long enough after the last dewormer. Those horses that are non- or low-shedders do not need to have FEC done again, and can be dewormed just twice a year at spring/fall. Horses who are moderate- or high-shedders should have FEC done summer and winter (so 3 months after the spring and fall deworming times) to see if they have developed worm burdens that would necessitate deworming. Additional FEC can be done at spring/fall to see “where they are” but these horses should be dewormed at those times regardless of the results. Lastly, facilities need to consider doing FECRT on a handful of horses that have parasite burdens in order to start to look for resistance to dewormers in our area. Incorporating these newer strategies into your deworming program will help create a bespoke deworming protocol for each horse leading to decreased administration of dewormer in most horses (80%) and therefore financial savings in the long run. Most horses will require less deworming treatments each year while those that would benefit from additional treatments (approximately 20% of horses) will be identified, leading to their improved health.

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