Question: Why are broodmares so prone to colic, and what colic causes are most common for them?

Dr. Katy Dern, Rood and Riddle Equine Hospital: According to the Centers for Disease Control, 1.4 percent of human delivery hospitalizations in the United States in the year 2014 developed what are characterized as severe maternal morbidities. This means that, even in closely supervised and intensively managed births, 1.4 in every 100 women developed potentially life-threatening complications. Parturition (birth) has potential consequences for the mother, and broodmares are no exception to this biologic reality.

Dr. Kathryn Dern

When we discuss colic (abdominal pain) in the broodmare, the cause of the pain can be broadly divided into two categories: pain originating from the gastrointestinal tract and pain originating from the reproductive tract.

Colic signs attributable to the gastrointestinal tract are a common phenomenon in the broodmare, and can be further subdivided into those conditions seen prior to foaling and those seen in the post-parturient time period (after foaling). Prior to foaling, causes of colic include mild discomfort due to expanding uterine size and fetal movements, as well as displacements or abnormal motility of the large colon, cecum, or small intestine. Mares exhibiting colic secondary to fetal movements or impingement of the gravid uterus on the gastrointestinal tract will usually not have dramatic changes in their vital parameters (heart rate, respiratory rate, mucous membrane color), and will respond to analgesics (pain management). If the mare's colic signs do not respond to pain management or increase in severity, she may have a gastrointestinal issue which can be life threatening to her and/or the foal. In either case, veterinary evaluation is important to differentiate between mild and more severe forms of colic, and to ensure that more aggressive medical and surgical interventions can be instituted if necessary.

Although our research has clearly shown that post-foaling broodmares are likely to develop large colon volvulus, we unfortunately have not yet determined exactly why they are prone to this disease. Common sense dictates that the presence of additional “room” in the abdomen post foaling must play a role, but this unfortunately does not account for the LCV cases we see in geldings, show horses, or preparturient [pregnant] mares.

Recent investigations into the role of intestinal microbiota in the development of colic suggest that significant changes in the fecal microbiota precede the development of colic. The changes in the bacterial population observed in the fecal samples of mares that developed colic are consistent with changes seen in both dysbiosis (imbalance in gastrointestinal bacteria) and inflammatory intestinal disease in other species, including humans. Further investigation into the role of intestinal microbiota in the development of large colon volvulus will hopefully allow us to not only fully characterize the disease process, but eventually identify at-risk mares and intervene prior to development of colonic displacement or volvulus.

Reproductive causes of colic are also common in the broodmare, and determining whether colic signs are gastrointestinal or reproductive in nature is one of the primary goals of the colic exam. In the pregnant mare, colic signs attributable to the reproductive tract can range from mild, medically manageable colics due to fetal shifting and increased fetal size, or abdominal discomfort can be a sign of more life threatening conditions such as uterine torsion or preparturient uterine artery hemorrhage. As with all signs of colic, evaluation by your veterinarian is indicated if your mare's colic signs do not resolve or increase in severity.  On the farm, your veterinarian may perform a physical, rectal, and/or ultrasonographic exam to determine if referral is indicated.

In the post foaling broodmare, causes of colic signs attributable to the reproductive tract include mild colic signs due to normal uterine contraction and involution, or more severe colic signs secondary to uterine artery rupture, uterine tears, invagination of a uterine horn or uterine prolapse. In the case of uterine artery rupture, the mare will often show signs of abdominal pain if the hemorrhage is limited to the broad ligament (soft tissue structure which suspends the uterus within the abdomen), as the hematoma dissects through the ligament itself. If she is bleeding freely into her abdomen however, she may not show signs of colic, rather exhibiting a high heart rate, anxiety, and increased respiratory rate consistent with blood loss. In these cases, a thorough physical exam, rectal palpation, abdominal ultrasonography, and abdominocentesis (analysis of a sample of the abdominal fluid) can be critical in determining whether or not the mare is actively hemorrhaging.

Lacerating or tearing the cervix during foaling is usually not painful and is commonly found later when the mare is spec'ed or when she is cultured. Manual examination of the cervix is required to definitively diagnose a cervical tear, which are usually repaired after the initial swelling from foaling has subsided (approximately three weeks after parturition).

It is important to note that just because a mare had an uneventful foaling does not mean that the foal didn't damage segments of the reproductive or gastrointestinal tract during parturition. In all cases of broodmare colic, evaluation by a veterinarian experienced in broodmare disorders and timely referral, if necessary, are critical to survival of both mare and foal.

Dr. Katy Dern is originally from Colorado and Montana. She attended Washington State University for her undergraduate work, and Colorado State University for her veterinary degree. Following graduation from CSU in 2012, she completed an internship at Peterson and Smith Equine Hospital in Ocala, followed by an internship at Rood and Riddle Equine Hospital. After her internships, Dr. Dern completed a three-year surgical residency at The Ohio State University, while also earning a Master's of Science Degree. She became board certified in equine surgery in 2018 and has been the surgeon at Rood and Riddle's Saratoga hospital since 2017. 

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Question: Sometimes stall rest is part of a horse's recovery program but some horses don't tolerate it well and may even self-injure. What makes them do this, and what can be done about it?

Dr. Lindsey Rings, Rood and Riddle Equine Hospital: Stall rest can be a very important and necessary part of your veterinarian's treatment plan for your horse and finding ways to make this time less stressful for you and your horse can be a challenge. Stall confinement can lead to the development of unwanted behaviors such as cribbing, weaving or stall walking. To help to avoid these behaviors, efforts to keep your horse engaged or entertained throughout the day should be utilized.

As herd animals, horses benefit from the companionship of other equids. Stall rest can make this difficult to impossible. Placing a calm companion animal within eyesight of a stall-rested horse can be of benefit and can help to reduce the stress in the stall confined horse. If a companion horse in an adjacent stall is impractical or impossible to provide, the placement of a shatterproof mirror in the stall may be of benefit. Horses that engage with their reflection are found to have reduced stress and anxiety.

Dr. Lindsey Rings

Toys placed in your horse's stall can occupy their down time. Commercial horse toys are available on the market and some even dispense treats or feed to your horse. The addition of stuffed animals, traffic cones, or make-it-yourself stall toys can also engage your horse's mind during confinement.

Adjustments to your horse's diet should also be implemented while maintaining a horse on stall rest. A stall-rested horse may not require the same caloric intake as they did while being more active. Therefore, reductions in concentrate/grain intake should be implemented. The use of a slow feeder or nibble net can extend the amount of time a horse spends consuming their hay and this can help to reduce their unoccupied time.

In a horse that is behaving in an unsafe manner towards either itself or its human care takers or whose behavior has remained retractable to management changes, the use of pharmaceuticals should be considered. Medications such as acepromazine, reserpine or fluphenazine have classically been used to reduce anxiety or induce long term sedation in stall confined horses. The use of trazadone orally is relatively new and seems to offer a safe and effective means to facilitate confinement and enhance calmness. Other products such as alpha-casozepine (Zlykene), magnesium sulfate and herbal combinations are also available and can be effective when used appropriately. Always consult with your veterinarian prior to starting treatment with any of these medications or supplements.

While stall rest is never easy for the horse or its human caretakers, there are several key areas of consideration that can help to make this event much less stressful on all involved.

Dr. Lindsey Rings aspired to be a veterinarian since she “could ride around in a car” with her mother, Marylou, who has a farm animal ambulatory practice and her father, Mike, an Internal Medicine Specialist himself.

After graduating from The Ohio State University's College of Veterinary Medicine in 2012, Rings, a Columbus, Ohio native, interned in New Jersey before completing an internship in 2014 at Rood & Riddle Equine Hospital in Lexington, Kentucky. After completing the internship, Rings returned to her alma mater and completed a three-year residency in Equine Internal Medicine while earning her Master's degree in Comparative and Veterinary Medicine.

 Dr. Rings practices at Rood & Riddle in Saratoga hospital as an internal medicine specialist working heavily with ambulatory veterinarians and other veterinary specialists.

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Question: It seems chiropractic care is becoming more popular and accepted in the veterinary community in recent years. What types of issues can this therapy address well, and when is it not a good fit?

Dr. Heath Soignier: “Chiropractic” therapy is very common in the human world and it is beginning to be accepted in the veterinary world. Veterinary spinal manipulative therapy, or more commonly known as “chiropractic” care, is a holistic approach as treatment for injuries, body soreness, etc. and should also be considered a preventative therapy. Documented science backs the effectiveness of manipulative therapy. Spinal manipulation is a safe and effective treatment modality for animal patients. It can and does affect the nervous system directly and indirectly which allows the therapist to think about neuro-anatomical function of the patient. As integrative therapies are being sought after more often, it is important to remember that complete workups of a patient and a common-sense approach to treatment is advised.

A common misconception is that a bone is “out of place.” It is better described as a lack of mobility or restricted motion of a joint through normal range of motion. The goal of a manual chiropractic adjustment is to bring motion into a joint that has not been moving correctly or effectively throughout its entire range of motion.

These joints (motion units) are palpated and evaluated for motion or lack thereof, as well as heat and tenderness. An adjustment is defined by experts as a “high velocity, low amplitude thrust into a specific direction of a specific joint.” When an adjustment is made, there are a few things happening to the specific joint that is being manipulated. These include breaking up adhesions, releasing of synovial folds and stimulation of receptors in and around the joint. It is important to realize that these joints are being manipulated by mere millimeters. By stimulating muscle receptors, the tone of muscles, tendons, and surrounding tissues are also affected. This can help in preventing some tendon injuries where an equine athlete may have some tightness in a muscle that is not clinically showing any pain, but the added tension under stress can lead to an injury.

This treatment modality is most commonly looked into after conventional veterinary care has not resolved pain or discomfort for the patient. Some common indications for this therapy could be unresolved lameness, sudden behavioral changes, sports injuries, or it may be used as a complimentary therapy. Some patients are evaluated for overall conditioning and any signs of pain or discomfort to areas over the body such as temporomandibular issues. Muscle pain and tone can be indicative of signs of joint restriction/dysfunction.

A major contraindication of treatment would be a fractured bone within a joint segment. Other contraindications would include neoplasia, pyrexia (fever), sickness, or hemorrhage. Being able to perform any adjustment will always depend on patient cooperation. Safety for the patient as well as the therapist must always be a priority.

Spinal manipulative therapy is more commonly being sought after now due to increasing drug regulations in equine athletes. A more holistic approach is becoming widely accepted in the equine industry. These therapies can help our equine athletes and offer a safe and effective treatment.

Dr. Heath Soignier was raised on a small farm in Bosco, La. After working at a mixed animal veterinary practice during high school, he decided to attend Louisiana Tech University to pursue an Animal Science undergraduate degree. He earned his degree in 2006 and continued his schooling at St. George's University School of Veterinary Medicine and completing a clinical year at Louisiana State University School of Veterinary Medicine in 2012. Dr. Soignier completed his ambulatory internship with Rood and Riddle in 2013 and Rood and Riddle as an associate. Dr. Soignier's special areas of interest include reproduction, neonatal medicine, and dentistry. In 2019, he became a certified veterinary spinal manipulative therapist.

When not seeing patients, Dr. Soignier enjoys spending time with his wife Catherine and his daughter Lucia on their small farm in Georgetown, Ky. He also is an avid sports enthusiast and outdoorsman.

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Question: What is LASER therapy?

Dr. Daniel Devis, Rood and Riddle Equine Hospital: The word LASER is actually an acronym of the expression “light amplification by stimulated emissions of radiation.” In other words, a LASER is a machine capable of producing a high and focused energy beam from a light or energy source. When talking about LASER therapy, we talk about the use of light energy that will focus in a specific area of the body to promote healing, repairs soft tissue injuries, and can even have some level of analgesia and anti-inflammatory response.

You should know that laser therapy is controversial and its results can be inconsistent, and of course it does not work instantly. On the contrary, the results from LASER therapy can take time to be noticed. You should always consult your veterinarian before deciding to use this type of treatment in your horse.

Dr. Daniel Devis

There are four different types of LASER levels, also known as “classes.” Each class represents a different amount of energy strength, and each class will tell you how harmful they can be to the naked eye.

LASER Class I can be found within your typical household and office equipment, such as laser printers, CD players, DVD players, etc. They produce a low level of energy that can cause very little damage to the eye.

LASER Class II are also widely used in daily life, and you can find them inside the bar code scanners at the grocery store and are commonly used during presentations as “laser pointers.” This type of laser represents a low risk of damage but it can be harmful if pointed to the eye for prolonged periods of time.

LASER Class III and IV are the ones used within human medicine and veterinary medicine, and the only difference between the two is the amount of power they produce. While Class III will go up to 500 milliwatts, Class IV lasers will go from 500 to thousands of milliwatts. Direct exposure to the eye with one of these lasers can be very dangerous and cause severe damage to the retina.

In veterinary medicine we encourage our clients to use regenerative laser therapies, like a Class IV type LASER, to help with non-healing or chronic wounds, as well as soft tissue injuries like ruptured tendons and ligament tears. LASER therapy can also be used post-surgery to speed up the healing process from the incision. It can also be used to repair fiber pattern and break scar tissue from old chronic injuries. LASER therapy can even be used in horses with joint damage (arthritis) by stimulating collagen regeneration.

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QUESTION: What is the veterinary perspective on the new pre-sale medication restrictions in force at public auctions in the United States?

DR. BART BARBER: From this veterinarian's perspective, the changes that the sales companies have made are positive. The limitations that have been imposed add a degree of confidence to buyers while still allowing sellers and veterinarians to fully treat horses as needed with only a few exceptions.

Dr. Bart Barber

There are some subtle differences but the changes for both sales companies are very similar. One of the new rules that each have applied is that only one non-steroidal anti-inflammatory drug (NSAID) and one corticosteroid may be used. There can be no stacking of drugs within the classes. There are lots of drugs in each of these categories and they have similar actions and effects within each class. That said, there are differences that make drugs in each of those classes superior for treating specific conditions. For instance, one NSAID is preferred to treat pain associated with colic while another is preferred for musculoskeletal pain. Certain steroids are better suited for treating allergic reactions while others are best at treating head trauma. The point is that there are reasons why one NSAID or corticosteroid is chosen over another and why there are several different choices.

In the rare case that a horse has already been treated with one of these medications for a specific condition and another condition arises for which another medication in the same class is needed, decisions will need to be made. First and foremost the horse will be taken care of. It is important to point out that this situation would not automatically disqualify the horse from being sold. A positive test for multiple NSAIDs or corticosteroids merely gives the buyer the right to rescind the sale. The goal of the new regulations is not to limit treating horses appropriately but to limit indiscriminate stacking of NSAIDs and corticosteroids, which is in the best interest of the buyers, the sales process, the industry and, ultimately, the horse. It's a good change. When the situation described above arises, it will be in the best interest of all parties to come together, use good judgment and horsemanship to determine intent, the best interests of the horse, and whether or not the process was compromised. These occasions will likely be rare and I believe that even in these instances we will be able to care for the horses without compromising the intent of the rules.

Bronchodilators, including clenbuterol, have been limited in that they have been completely banned for a time period prior to the sale. There is a potential for abuse of these medications and again this is a positive change to protect the horse. When this change was announced some chose to not use this class of medications in horses at any age, for any condition and I believe that is a mistake. Taking this out of a veterinarian's toolbox for use in foals could have fatal consequences. There are legitimate uses for these medications and they should be used when they are warranted. The sales companies have not limited their use when appropriate for age and condition, they have merely asked for disclosure.

The balancing of allowing for appropriate use and imposing rules to curtail abuse is difficult. In this case it has been well thought out and will benefit all involved.

Dr. Bart Barber, DVM, is a shareholder in Rood and Riddle's veterinary practice and specializes in reproduction, primary and preventative ambulatory care, as well as operations at Rood and Riddle Veterinary Pharmacy.

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QUESTION: Why is it important to have a veterinarian perform dental work on your horse?

DR. BRAD TANNER: Responsible horse owners have mental checklists of the things that need to be done each year for their horses. These include deworming, vaccinations, Coggins test, health certificate and of course annual floating. The annual float is a treatment for the condition of sharp enamel points. No treatment, be it antibiotics, anti-inflammatories, etc. should be administered without an examination and proper diagnosis.

Why should a dental float be any different?

Dr. Brad Tanner

The tooth of a horse continues to grow (erupt) throughout life. Those areas of the tooth that do not get worn away become long and sharp. Left to their own devices these sharp teeth may cause cuts in the cheeks and tongue (see below). These sharp teeth cause increased discomfort in performance horses as bit and bridle change head carriage which forces increased contact of these teeth with the cheek tissue. Dental floating is the necessary treatment for this common condition in the horse.

While responsible owners are correct to have their horse's teeth checked annually, the floating is not the most important thing happening — it is the exam. A proper dental exam performed by your veterinarian can provide insight into your horse's general health as well their oral health.  This veterinarian has spent years of training in anatomy, physiology, medicine, surgery, imaging etc. and is equipped to recognize, diagnose and treat oral pain.

The dental examination will include assessing facial symmetry, bone enlargements, lymph nodes, draining tracts, maleruptions, malocclusions, soft tissue lacerations and abrasions. The exam will also include a close inspection of each tooth surface with a dental mirror or an oral camera. These close looks often show painful problematic teeth with cracks, fractures or feed packing that may need to be investigated with additional imaging.

Recognition of abnormal dental wear or other pathology may be indication for dental radiographs or a CT scan to further investigate problematic teeth. These imaging modalities are common practice in human medicine as the ADA (American Dental Association) recommends radiographs every couple of years, and with increased access to quality digital radiography this is also becoming more common in horses.

This image shows damage to a horse's tongue that has arisen from sharp points on the teeth. Photo courtesy Dr. Brad Tanner

Horse teeth do develop cavities and these can lead to fracture, pain, and sometimes sinus infections. These problems can be avoided with early detection and treatment. The treatment for these is cavity fillings (restorations) and can be done as a routine standing procedure. Our goal is to preserve functional occlusion of the teeth and allow continued grazing. Given the opportunity horses on pasture will graze up to 16 hours daily.

Dr. Brad Tanner received his DVM from Auburn University in 2005 and completed an internship at Rood and Riddle thereafter. He is a shareholder in the clinic, where he focuses on advanced dentistry, primary care and reproduction. Tanner became board certified in equine dentistry in 2019.

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QUESTION: What is “parrot mouth” in a horse, and can it be resolved?

DR. BRAD TANNER: Horses come in all shapes and sizes and so do their mouths. A parrot mouth describes the upper lip that hangs forward and down ahead of the lower lip. This term is synonymous with overbite malocclusion of the incisors of a horse. As the top jaw grows, if it grows at a faster rate than the lower jaw, the front teeth will be extended forward and no longer make contact with the lower incisors. This is what gives the characteristic large, goofy lip of the top jaw that we so often call “parrot mouth.” When an owner raises the top and lower lips, you will notice that those front teeth often times barely contact or sometimes don't contact at all.

Dr. Brad Tanner

Is it a problem?

Yes and no. While it's cosmetically unpleasant to look at for some people, does it really affect performance? The answer is that it doesn't if managed correctly. These horses will continue to eat, they will continue to grow and they will not be skinny because of this malocclusion. However, this can be a problem for some horses. The question is whether the only malocclusions present impacting the incisors; if the front teeth that no longer contact, it's possible the entire top jaw could have shifted forward, which can create a ripple effect. This means that the first cheek tooth on top may no longer be grinding on the first cheek tooth on the bottom. Conversely, the last cheek tooth on the bottom may no longer be chewing in contact with the last cheek tooth on the top and the results of this will be large hooks and excessive growth of these teeth.

This image shows the “hooks” that can appear when the top and bottom jaws don't align properly and part of a tooth is not worn down as normal. Photo courtesy Dr. Brad Tanner

This can cause significant problems and pain for horses, as these large hooks cause collateral damage to the soft tissues, gums, and cheeks. This is compounded when a bit is applied to the horse's mouth and a rider asks the horse to put the head into a frame/collection, causing increased contact of these teeth overgrowths and the soft tissues surrounding them. In Thoroughbred racehorses the effects are less dramatic than in dressage and other disciplines. This is due to the fact that racehorses run largely on looser reins with an extended head and neck rather than in flexion of the poll.

Can it be corrected?

While this is a permanent deformity in adult horses, it can be corrected in young growing foals. Correction should take place between four to six months of age, ideally. As the maxilla (top jaw) is growing ahead of the mandible (lower jaw) at a higher rate, an orthodontic appliance can be applied with orthodontic wires to halt the growth of the maxilla allowing the mandible to catch up. Additionally, an inclined plane is applied in the form of an aluminum plate allowing the lower teeth to engage with it during each chewing motion.

Corrective devices can fix parrot mouth if it is caught early in a horse's life, before skeletal development is complete. Photo courtesy Dr. Brad Tanner

Corrective devices can fix parrot mouth if it is caught early in a horse's life, before skeletal development is complete. Photo courtesy Dr. Brad Tanner

Once the skeletal development of the horse is complete, there is no way to effectively correct the overbite/parrot mouth malocclusion.

How do you manage this problem long term?

Long term management of these malocclusions should be focused on effectively floating and reducing the large overgrowths. These are the overgrowths that form because some teeth are not in occlusion and chewing along one another. Normally, the teeth will grind and wear out at the same rate but when one tooth is not in contact it is allowed to continue to grow through the life of the horse at a rate of three to four millimeters per year. Left unchecked, this can wreak havoc on the horse's mouth and be a painful situation.

Long term management often will require routine floating examinations at six-month intervals on horses that have these types of malocclusions. So long as these are managed effectively the horse will be able to have normal dentition and perform at a normal level. Horses will not run faster or slower because of the parrot mouth. So long as they are managed effectively it should have no influence on performance.

The heritability of a parrot mouth has been called into question for some time. It's often viewed as a heritable trait that can be passed along from generation to generation and is therefore undesirable in breeding stock. Unfortunately, while much research has been done in this area, the heritability of overbites/parrot mouth is a very complex genetic trait. Recent studies have shown there are complex patterns of genetic alleles that are involved in the expression of the genes that lead to this defect. It is difficult to pinpoint exactly which foals could develop this trait and which sires are more or less prone to passing it along because of the complexity of alleles that are necessary to give this result and deformity.

In summary, parrot mouths are not really a big deal for a lot of horses. They have managed to survive for millennia this way and will continue to eat and graze. Proper management of a mature horse with parrot mouth will lead to decreased dental problems, decreased pain, and better performance in a show ring or racetrack. Recognition at an early age does allow for surgical correction and normal dentition for the rest of the horse's life.

Dr. Brad Tanner received his DVM from Auburn University in 2005 and completed an internship at Rood and Riddle thereafter. He is a shareholder in the clinic, where he focuses on advanced dentistry, primary care and reproduction. Tanner became board certified in equine dentistry in 2019.

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QUESTION: What does it really mean when a veterinarian talks about a racehorse having “bone bruising”?

DR. A.J. RUGGLES: If you been around racehorses you likely have heard the term “bone bruising.” Despite its common use the term is really not entirely accurate in most cases. What your veterinarian is likely referring to is Non-Adaptive Stress Remodeling (NASR). You can see why the term bone bruising is more commonly used.  While a true contusion (bruise) of the bone–manifested by lameness and characteristic findings of edema in the bone on magnetic resonance imaging–occurs, it is much less common than NASR.

To understand NASR and its causes, an understanding of bone anatomy and physiology is necessary. Most people think of the skeleton as an inert frame that muscle, tendon and ligaments attach to allow movement or as protection for vital organs. While the skeleton performs these functions, it also is a very dynamic system than is undergoing a constant process of removal and replacement as the horse grows in size and is being trained.

Dr. Alan Ruggles

It is easy to realize the skeleton of a foal is different than the skeleton of a 3-year-old. Not only has the horse grown in stature, but the structure of the bone itself is altered to fit its athletic activity. For example, the front of the cannon bones in the front legs of a trained 3-year-old will be thicker and denser compared to a 3-year-old that has never trained and only exercised at pasture. Likewise, an older broodmare who has been out of training and has had many foals may have a relatively weaker skeleton compared to the actively trained racehorse due to the absence of training and the depletion of calcium from her skeleton due to multiple lactation cycles.

When an athlete trains, whether it is a person or horse, receptors between the cells within the bone recognize the changes in load in the bone and send a signal for the bone to change its geometry and replace damaged bone to fit this new activity. This normal process is called stress remodeling. During this process original bone is removed and new bone is produced to replace it. Imagine a long bone like the cannon bone as a cable of a suspension bridge and within the cable are multiple smaller wires cables.

When bone changes its shapes or repairs injured bone each of these original smaller wires (primary osteons) are removed and then replaced with new bone (secondary osteons). During this process the removal phase occurs at a rate 50 times faster than the replacement rate. The rate of remodeling is influenced by the stimulus of training and when it occurs successfully, the process is necessary and positive. Another response of bone is to make itself larger quickly to resist mechanical loads by putting down relatively weaker (woven not cortical bone) on the surface of a bone. This is what causes the bump in bucked shins.

Most of the adaptive process of the horse skeleton via stress remodeling occurs without incident but sometimes the process gets overwhelmed and manifests as lameness. If there is a failure of the normal stress remodeling process, there can be an accumulation of damaged bone which can cause lameness, micro fissures and fractures.

An image captured from a bone scan shows an area of concern

Sometimes the lameness is obvious and easily detected, such as a bucked shin of the front cannon bone. Sometimes the lameness is obvious but not easily detected on a physical exam as with humeral, tibial or ilial stress fractures. Most commonly, at least in our practice, the horse has clinical signs of poor performance: perhaps a “crabby gait” or not changing leads. The horse is often lame in more than one limb, which makes detection of the problem more difficult.

A careful lameness examination with diagnostic nerve blocks is recommended to ferret out the cause of the lameness. The nerve blocks help us localize the source of lameness and help us direct our diagnostic imaging such as radiographs, ultrasound, nuclear scintigraphy, MRI or computed tomography.

Nuclear scintigraphy (commonly known as bone scan) is very helpful in detecting stress remodeling since it is best suited to detect excess bone metabolic activity which occurs during stress remodeling and stress fractures.

Radiographs and computed tomography may reveal increased density of the bone with associated bone resorption especially in the condyles of the distal cannon bone. There also may be changes in the bone contour and the development of fractures. Magnetic resonance imaging with high field magnets (MRI) is helpful to determining the health of the cartilage as well as bone and associated soft tissue structures. Ultrasound is not generally helpful in diagnosis or management. Newer technologies such as standing computed tomography and PET scans give detailed 3D images of bone and show promise but are not yet available for widespread use and are still undergoing clinical validation in the management of stress remodeling.

An MRI shows an area of bone bruising

If your horse is diagnosed with bone bruising, it likely has a form of NASR. That is the bad news. The good news is most cases do not develop clinical fractures and therefore are not treated surgically and responds to rest. Horses that develop fractures such as dorsal cortical fracture of the cannon bone or condylar fractures of the cannon often are treated surgically for best outcomes. Other hairline fractures of the humerus and tibia are treated with rest alone. The majority of cases in racehorse affect the bottom of the cannon bone or the third carpal bone and are treated with rest.

An image from a radiograph shows bone bruising

Typically, they are given 60 to 90 days off and pasture activity is recommended. The purpose of the period of rest is to allow the skeleton to catch up with the signals that have been sent by training so the stress remodeling process can finish to better allow the bone to withstand the rigor of training and racing. Remember, during stress remodeling bone resorption is 50 times faster than production.

Timing on when to turn the horse out obviously depends on the degree of lameness. If the horse shows any potential for a fracture being present, negative follow-up radiographs are needed before turnout etc. All these decisions are unique for each horse and should and be made in concert with your veterinarian. Treatments such aspirin and isoxsuprine and some over the counter supplements may help during the process by improving blood flow to the bone. Drugs which inhibit the natural bone remodeling process such as bisphosphonates, in my opinion, should not be used in cases of NASR and should only be used as labeled.

The vast majority (80% plus) respond to a period of rest with turnout. This is a tried and true method of trainers who have for decades given horses time off usually in the winter. These methods still work today of course. Proper diagnosis of NASR is important in my opinion to make sure you know what you are treating and to make sure no other condition exists that might require a different intervention.

Next time you hear that a horse has bone bruising, remember it is likely a form of NASR and hopefully you will have a better understand of the natural process of bone turnover and how it is related to this syndrome.

Dr. Ruggles specializes in orthopedic surgery and lameness. In addition to his experience as a practicing veterinarian, he served as a faculty member at New Bolton Center and at Ohio State University before joining Rood and Riddle in 1999. He is a partner in the hospital and is part of the AAEP “On Call” media program.

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