Colic Part 1 – GI Tract Anatomy

 The word colic sets a horse owner’s heart racing like almost no other word.  It is scary to see your equine friend so distressed and uncomfortable. While most colics are mild and can be treated on the farm, other colics can be live threatening and may require intensive treatment or surgery.  Some can even be fatal. The word colic simply means abdominal pain.  The gastrointestinal tract of the horse is large and varied with lots of places for a problem to develop.  Thus there are many causes of colic.  When your veterinarian evaluates your horse for colic, one of their goals is to determine the reason your horse is experiencing abdominal pain and to try and differentiate the mild cases from those that need more intensive care.  In this multi-part series on colic, we will be discussing the anatomy of the horse intestinal tract, different causes of colic, and different treatments for colic.

 

PART 1: ANATOMY OF THE EQUINE GASTROINTESTINAL TRACT

 

The horse has a large and varied gastrointestinal tract.  Some portions of the tract are similar to ours and other portions are very different.  Horses chew their food in their oral cavity or mouth.  Once they swallow, the food travels down the esophagus to the stomach.  Horses have a stomach that is fairly similar in function to ours.  It is about the size of a basketball.  Cells in the lining produce acid and other products to start the initial breaking down of their food.  Feed material then passes into the small intestine.  There are three parts of the small intestine: the duodenum, the jejunum, and the ileum. Food is further digested in the small intestine. A horse has over 70 feet of small intestine.  Feed material then moves into the cecum.  The cecum is equivalent to the human appendix, but where as our appendix has little necessary function, the equine cecum is very large and important.  It is a big comma shaped organ that takes up most of the right side of the abdomen and is a place where bacteria start to break down the cellulose in plant material.  Unlike us horses are able to obtain usable nutrition from plant material like grass and hay.   This is because they have bacteria in their gastrointestinal tract that are able to break down cellulose. After the cecum, feed material moves into the large intestine.  The large intestine in the horse is very large (hence the name) and actually contains four parts.  It starts on the right side of the abdomen extends over to the left side, continues down the left side to the area near the pelvis at the back of the abdomen.  It then makes a 180-degree-turn and returns to the front of the abdomen near the diaphragm.  It then goes back over to the right side and along the right side of the abdomen. The large intestine is not attached to the body wall or any other portions of the GI tract for much of its length.  It can weight up to 100lbs when filled with feed.  It is another site of bacterial breakdown of plant material.  Feed material then enters the short transverse colon before entering the small colon where it is formed into fecal balls before leaving through the rectum and out the back end of the horse.

 

 

 

 

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Sarcoids

Equine Sarcoids

What is a sarcoid?  Should I be worried if my horse has one?  What is the best way to treat sarcoids?  These are the questions many horse owners ask if their equine companion is diagnosed with a sarcoid.

A sarcoid is a skin neoplasia (abnormal growth).  A characteristic that differentiates sarcoids from other skin growths is that there is a proliferative epithelial component1.  This means that there is excessive growth of the outermost layer of the skin.  Sarcoids are typically considered benign tumors because most are slow growing and do not affect the overall health of the horse, however there are very rare exceptions which can become malignant.  Sarcoids are classified into different types based on how they look and act.  These types range from occult saroids, which appear as a flat hairless region of skin that may be unchanged for many years, to malevolent sarcoids that infiltrate under the skin and grow rapidly.  Verrucous or wart-like sarcoids and nodular or round, spherical sarcoids are other common types.  Mixed sarcoids contain characteristics of multiple types of sarcoids.  For example they may be round with a wart-like surface.  Many sarcoids can be accurately diagnosed based on what they look like, however in order to be completely certain of a diagnosis, a section of the suspected sarcoid must be submitted and evaluated under the microscope.

Extensive research has gone into determining the cause of equine sarcoids.  The development of a sarcoid is likely due to a combination of factors including genetics, exposure to certain viruses, and trauma.  Certain breeds of horses and the presence of particular genes within a horse breed have been shown to be associated with increased incidence.  In one study Quarter horses were found to be at increased risk, while Standardbreds had a much lower risk2.  Exposure to bovine papilloma virus, a virus that causes warts in cattle, has also been shown to be associated with the development of sarcoids, although only certain horses affected with this virus will develop a sarcoid3.  Sarcoids are often found at the site of a previous wound, suggesting that trauma may also play a role in their development.  It is likely a combination of multiple factors that results in the development of a sarcoid.

Treatment of sarcoids can be challenging.  No one treatment is fool proof and often multiple treatments are combined.  Sarcoids can re-occur with a vengeance, so continued dedication to treatment on the part of the owner and veterinarian is very important.  Many scientific studies have been conducted to evaluate treatment methods for sarcoids.  It can be difficult to compare these studies as they often look at different types of sarcoids.  You can imagine that the success rate published with one technique that reports removal of small sarcoids that have never been treated before would have better results that a study looking at a different treatment that was used on large sarcoids that have already been treated many times and have re-occurred.  If your horse is diagnosed with a sarcoid, you and your veterinarian will weigh multiple factors to determine the best course of action for your horse.

Some small, flat sarcoids that are not in a location that causes a problem for the horse or that interferes with riding may just be left alone and monitored.  It is important to keep a close eye on these sarcoids.  If they start to grow, they should be treated before they are allowed to become large.

Simply removing the sarcoid is one of the least successful treatment methods.  Often the sarcoid rapidly returns and is even larger than before it was removed.  Studies looking at surgical removal alone report re-occurance rates (the sarcoid comes back) of up to 82%4.

Removal with a surgical laser has a much better reported success rate.  The laser causes less trauma and reduces the spread of abnormal tumor cells.  This procedure is quick and often does not require general anesthesia (where the horse is laid down and kept completely asleep for the procedure).  It does however require that the horse be transported to a veterinary hospital for treatment.  A large study reported a re-occurance rate of 38%5.

Cryotherapy or freezing of the sarcoid tissue has been one of the most common treatment methods.  This treatment involves freezing the tumor tissue with a probe chilled by liquid nitrogen.  It can often be done on the farm, but multiple treatments are necessary especially if the sarcoid is large.  Early studies reported good success rates, but a more recent study that looked at outcomes over a longer time period reported high re-occurance rates4.

Sarcoids can also be treated by injection with the chemotherapy drug cisplatin.  This treatment can also be combined with surgical removal or surgical laser removal.  Reported reoccurrence rates vary between 13-66%1.  Topical application of the chemotherapy drug 5-flurouracil was shown to be successful when applied daily for 15 days on small sarcoids.  This cream also causes significant inflammation and discomfort to the site where it is applied, so repeated application can be challenging as the horse is often resentful of its application4.  Xterra a product that contains bloodroot has also been reported to be successful, however there are no current scientific studies evaluating this product for the treatment of sarcoids.

Immunotherapies have also been used to treat sarcoids.  One type involves the injection of the cell wall of a certain type of bacteria.  This does not cause an infection with that type of bacteria, but does cause the body’s immune system to be super stimulated.  The immune system then recognizes the sarcoid as a tumor cell and attacks it.  These therapies require multiple injections and result in severe tissue swelling at the site of the sarcoid.  In rare instances severe and even life threatening anaphylactic (allergic) reactions can occur4.

Various types of radiation therapy have been used with very good results.  Reoccurrence  rates are as low as 1- 12.5% of cases.  Radiation therapy is very expensive and can only be performed at a few university hospitals.  Depending on the type of radiation therapy it can require multiple episodes of general anesthesia per week for 3-4 weeks or complete isolation of the horse for several days to weeks6.

After reading this long list of treatment options, it is likely easier to appreciate why it is important to discuss the multiple options with your veterinarian and determine the best course of action for your horse.  The good news about sarcoids is that they are very rarely life threatening and the majority do not affect a horse’s athletic potential.  With appropriate therapy most sarcoids can be successfully treated and your horse can go on to live a long, happy, productive life.

References

  1. Carr, EA. Skin Conditions Amenable to Surgery. Equine Surgery
  2. Angelos J, Oppenheim Y, Rebhun W, et al: Evaluation of breed as a risk factor for sarcoid and uveitis in horses. Anim Genet 19:417, 1988.
  3. Carr EA, Theon AP, Madewell BR, et al: Presence of bovine papilloma virus DNA in equine sarcoids in horses living in the Western United States. Am J Vet Res 62:742, 2001.
  4. Knottenbelt DC, Kelly DF, The diagnosis and treatment of periorbital sarcoid in the horse: 445 cases from 1974-1999. Vet Ophthalmol 3:169, 2000.
  5. Carstanjen B, Jordan P, Lepage OM: Carbon dioxide laser as a surgical instrument for sarcoid therapy: A retrospective study on 60 cases. Can Vet J 38:773, 1997.
  6. Byam-Cook KL, Henson FM. Slater, JD: Treatment of periocular and non-ocular sarcoids in 18 horses by intersitisal brachytherapy with iridium-192. Vet Rec 159:337, 2006.

Joint and Tendon Sheath Infections

Although a large wound across your horse’s chest can be rather impressive with exposed muscle and obvious bleeding, one of the most dangerous wounds your horse can sustain is a small wound on the lower limb that enters a joint or tendon sheath.  This type of wound may not be immediately recognized or considered important, but can be career and life threatening for your horse.

Joints and tendon sheaths are both synovial structures, which are cavities lined with cells that produce synovial fluid.  This fluid lubricates and provides nutrition for the structures within the joint or tendon sheath.  Joints and tendon sheaths have a variety of functions, but the most important is to help movement.  Joints occur between two bone ends and minimize friction and concussion as two bones glide or rotate in relation to each other.  Tendon sheaths wrap around tendons and lubricate and protect them as they travel over joints.

A wound that enters a joint or tendon sheath introduces bacteria.  Synovial structures are great environments for bacterial growth and are challenging locations for the body to fight infection.  Once bacteria have been introduced and start to replicate the synovial structure is septic or infected.  A wound that enters a synovial structure may also introduce foreign material such as dirt, hair, or wood.  This foreign material is irritating and is a wonderful place for bacterial to collect and multiply.  One scientific study found that 33.8% of infected joints or tendon sheaths have foreign material present (1).  Joint or tendon sheath infection results in severe inflammation, pain, and lameness.  Infection within a joint can destroy the articular (joint) cartilage causing arthritis.   This can result in permanent and often severe lameness.  Joint infections that are not treated can also spread into the surrounding bone, which worsens the prognosis(1).  Infection within a tendon sheath results in inflammation and the development of adhesions or fibrous connections between the tendon and the sheath wall.  Adhesions prevent proper movement and cause pain.  Uncontrolled tendon sheath infections can also result in spread of infection into the tendons themselves(2).  Infected synovial structures are extremely painful.  If an infection within a joint or tendon sheath cannot be controlled it may even result in euthanasia.

Septic joints and tendon sheaths can be successfully treated, but the key is to start treatment early and to be aggressive. The first step is to determine if a wound enters a synovial structure.  With a fresh wound your veterinarian will prepare a location away from the wound to place a needle in the joint, or tendon sheath.  Thus if there is a wound over the outside of the fetlock joint, your veterinarian may clean and prepare a location on the inside of the fetlock joint.  The joint is tapped at this separate location and sterile saline is injected.  If saline exits through the wound, then the wound communicates with the joint.

If the wound is older and has sealed over, your veterinarian will evaluate your horse for lameness or extra fluid (effusion) within the joint or tendon sheath.  A sample of synovial fluid from the suspected structure is removed, analyzed, and cultured.  This procedure can also be used to determine how a synovial structure is responding to treatment.

If a wound enters a joint or tendon sheath, extensive flushing of the affected area, antibiotic therapy, and pain medication are the most important parts of treatment.  The best way to treat an infected joint or tendon sheath is by making small incisions to insert a small camera and separate flush cannula or tube into the joint (arthroscopy) or tendon sheath (tenoscopy).  With this procedure, the horse is anesthetized in an operating room and liters of fluid are flushed through the synovial structure while it is evaluated with the camera.  If foreign material or large clumps of fibrin (inflammatory material) are present, they can be removed.  Rainland Farm Equine Clinic is one of the few hospitals in the Western Washington area with the facilities and expertise to offer arthroscopic surgery.

If this minor surgery is not an option for an individual horse, the joint can also be lavaged by flushing saline through multiple large needles placed in different locations in the joint.  This type of treatment is more likely to be effective when performed soon after the injury.  Systemic (oral or intravenous) and local antibiotic therapy is also started.  Systemic (oral or IV) antibiotics are important, but are often not enough. There are several choices of local antibiotic therapy and your veterinarian will decide which options are best for your horse.  Antibiotics can be directly injected into the joint or tendon sheath.  Antibiotics can be repeatedly injected through a drain left in the affected joint or tendon sheath.

Regional limb perfusions with antibiotics are another option.  With a regional limb perfusion a tourniquet is placed above the affected joint.  Antibiotics are injected into a superficial vein in the limb below the tourniquet and the tourniquet is left in place for 30 minutes.  This procedure concentrates antibiotics in all of the tissue below the tourniquet.

All of this information sounds very scary, but many septic joints and tendon sheaths that are appropriately treated respond well.  Recent scientific studies looking at the outcomes of horses with infected joints and tendon sheaths report a survival rate of 73% – 90% and a return to athletic performance of 54%-81% (1,2,3,4).  Thus if you get prompt veterinary care, your horse has a good chance of recovery.  Wounds near a joint or tendon sheath are always an emergency.  At Rainland Farm Equine Clinic we recommend that you contact your veterinarian right away about any wound on your horse’s lower leg that goes all the way through the skin.

References

  1. Wright IM, Smith MR, Humphrey DJ, Eaton-Evans TC, Hillyer MH. Endoscopic surgery in the treatment of contaminated and infected synovial cavities. Equine Vet J 2003;35:613-9.
  2. Wereszka MM, White NA, Furr MO. Factors associated with outcome following treatment of horses with septic tenosynovitis: 51 cases (1986-2003). J Am Vet Med Assoc 2007;23:1195-200
  3. Walmsley EA, Anderson GA, Muurlink MA, Whitton RC. Retroscpective investigation of prognostic indicators for adult horses with infection of a synovial structure. Aust Vet J 2011;89:226-31.
  4. Taylor AH, Mair TS, Smith LJ, Perkins JD. Bacterial culture of septic synovial structures of horses: does a positive bacterial culture influence prognosis? Equine Vet J 2010;42:213-8.