Bog spavin is a common term for effusion in the horse’s tarsocrural joint. This painful condition describes inflammation and fluid accumulation in the joint capsule between the tibia and the tarsal bones in the hock.

Bog spavin is characterized by a ring of swollen lumps around the hock. When one of the swellings is compressed, the others expand as the fluid moves around the swollen joint.

Joint effusion in horses is usually connected to an underlying joint or connective tissue disorder such as osteochondrosis, osteoarthritis, traumatic injuries, chronic strain, poor conformation, or joint infection. Bog spavin develops most often in working horses and equine athletes.

Treatment for mild cases includes rest and anti-inflammatory drugs. In more serious cases, treatments may include corticosteroid joint injections, compression bandaging, and fluid drainage. In extreme cases, hospitalization may be required.

The prognosis ranges from good to guarded depending on the underlying cause and response to treatment. Prevention of bog spavin in horses requires avoiding injury, providing excellent nutrition, and allowing plenty of rest after exertion.

Bog Spavin in Horses

Bog spavin describes fluid accumulation and inflammation of the lining of the joint and the joint capsule (joint effusion) inside the horse’s hock. [1][2] The condition appears as a characteristic ring of swollen lumps around the hock.

This condition is known by multiple names, including: [2][3]

  • Tarsocrural joint effusion
  • Tarsocrural effusion
  • Talocrural effusion
  • Tarsal hydrarthrosis

Bog spavin specifically affects the tarsocrural joint (TC joint or tibialtasal joint), which connects the tibia (the long bone in the horse’s shin) with the tarsal bones in the hock. This joint is fundamental to equine locomotion (walking) and overall mobility. [1]

When a horse has bog spavin, fluid accumulates in the capsule between the bones, then pushes out of the tight space, resulting in visible swelling around the hock. These swellings are referred to as “bog spavins“. [4] Bog spavin can occur in one or both hocks of the hind legs. [3]

Causes

Bog spavin is the result of inflammation in the membrane that lines the tarsocrural joint. [3] It occurs when the synovial cavity (space between the two bones) becomes inflamed and causes swelling of the capsule that cushions the joint between the tibia and the hock. [4] In some cases, the cause remains unknown.

In general, bog spavin is a complication of another underlying joint disease. Possible underlying conditions include:

Osteochondrosis

Osteochondrosis is a disorder of bone development during the horse’s growth phase. In severe cases, this can result in osteochondrosis dissecans, where the cartilage separates from the underlying bone and forms a flap that causes further pain, inflammation, and joint dysfunction. [4][5]

Osteochondrosis is suspected as an underlying cause of bog spavin when it develops in horses under 3 years of age or shortly after the horse is broken or begins athletic training. Osteochondrosis typically affects both joints. [4][5]

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Osteoarthritis

Also known simply as “arthritis,” osteoarthritis is a degenerative joint disease characterized by the breakdown and eventual loss of cartilage. Arthritis is uncommon in the tarsocrural joint, so it is not one of the leading causes of bog spavin.

Osteoarthritis is suggested as a cause of bog spavin by marked swelling of the area and extreme pain in the hock during the flexion test. [1][6]

Arthritis can evolve from untreated osteochondrosis especially in cases where it progresses slowly or due to a traumatic injury to the joint. This cause of bog spavin is suspected in older horses and horses in heavy work. [1][6]

Traumatic injuries

Joint injuries particularly due to stops and quick turns or due to external trauma such as kicks or falls are a possible underlying cause of bog spavin. Specific injuries may include sprains, chip fractures, or more severe fractures in the tibia or bones of the joint space. [1][2]

Injuries are suspected as a cause of bog spavin when the condition develops in younger horses, horses in heavy work, and especially when only one limb is affected. Bog spavin secondary to injuries typically responds quickly and thoroughly to rest and anti-inflammatory drugs. [1][2]

Chronic Strain of the Joint

Chronic joint strain in horses is usually associated with either conformation issues or working on unforgiving surfaces over many years. This cause of bog spavin is suspected especially when bog spavin develops in older horses. [3]

Poor Conformation

Straight hindlimb conformation produces continuous stress on the cartilage resulting in trauma and wear in the joints. This is a suspected cause of bog spavin in cases where swelling is present in both limbs and the conformation fault is obvious. [1]

Infection

The hock is often in the path of the horse’s waste excretions (urine and feces) and the joint is close to the skin. As a result, wounds in this area are prone to infection, which are at high risk of progressing into the joint capsule. [4]

If a wound is suspected as a cause of bog spavin, prompt examination and treatment is recommended. In severe cases, infection may develop into articular sepsis (also called septic arthritis) which is a veterinary emergency. [4]

Hemarthrosis

Hemarthrosis describes bleeding into the joint as a result of trauma, blood disorders, joint disorders, or as a side effect of medications such as blood thinning medications.

The tarsocrucal joint is particularly susceptible to this condition because it is crossed by a large blood vessel. [6] Bleeding into the joint may appear as bog spavin until further diagnostics show the fluid is actually blood.

Vitamin and Mineral Deficiencies

Trace minerals such as manganese, copper, and zinc are important for supporting joint health and integrity. These minerals are components of enzymes that build and repair joint tissue. [7]

In addition, macrominerals such as calcium and phosphorus are important in bone development. [8]

Horses who are deficient in these nutrients are at greater risk of developing bog spavin and associated conditions. [2][3]

Risk Factors

The risk factors for bog spavin depend on the primary cause of the disease. In general, bog spavin occurs in horses of all ages. [3] It typically affects performance horses and others in heavy work, particularly those in sports that require a lot of stopping and side to side movement such as barrel racing and reining. [1]

There does not appear to be a predisposition based on sex or breed. Horses with poor conformation of the hind legs are more likely to develop bog spavin. [1]

Large horses or horses that carry more weight are also at greater risk of joint dysfunction that may result in bog spavin. [1]

Symptoms

Bog spavin is characterized by the presence of a swollen area around the upper edge of the hock. This swollen area divides into several pockets that protrude in several places around the joint. It may be easily confused with bone spavin, which is swelling below the hock.

In horses with bog spavin, when one swelling is compressed, the others increase in size as the fluid moves from one protrusion into another. This symptom varies in severity from subtle and difficult to confirm to significant enough to affect the appearance of the horse. [2][3]

Another common sign that alerts owners to this condition is lameness, although it is possible for a horse to remain sound with bog spavin. In cases where lameness develops, it can range from mild to severe. [1][2]

Bog spavin is sometimes painful to the touch but is always painful during flexion of the joint. [1] In some cases, lameness is not present at slower speeds, but may appear at faster speeds or when the horse is put to work. [1]

Severity

The severity of the condition depends on the extent of inflammation in the hock capsule. In mild cases, horses may continue working successfully without lameness. In severe cases, bog spavin can lead to significant disability. [1]

If left untreated, bog spavin can develop into osteoarthritis, making it likely lameness will become more severe over time. [1] Bog spavin may also be an indication that the horse has widespread joint disease. [1] In severe cases, the joint becomes heavily infected, which is a veterinary emergency. [3]

Diagnosis

Bog spavin ranges from asymptomatic to very severe. In the case of a severe joint inflammation, especially when the suspected cause is a wound, emergency veterinary attention is necessary. In mild or moderate cases, veterinary care is recommended. [3]

Diagnosis is based on the presence of the characteristic ring of swellings around the joint divided into several pockets. When one pocket is compressed, the others increase in size as the fluid moves from around. [1][6]

Diagnostic tools that your veterinarian may use to assess your horse include: [1][2][3][4]

  • Physical examination including flexion testing of the hock
  • X-rays
  • Ultrasounds
  • MRI
  • CT scan
  • Arthroscopy (visualizing the joint with a surgical camera)
  • Scintigraphy (visualizing the joint with radioactive dye)
  • Synoviocentesis (withdrawal and examination of fluid from the capsule)

Treatment

In mild cases, treatment consists of rest and anti-inflammatory medications, which typically lead to rapid improvement. In more severe cases, ongoing treatment is necessary. In the case of articular sepsis, hospitalization with intensive treatment and monitoring is required. [1]

Treatment options your veterinarian may pursue include: [1][6]

Dietary Support for Recovering Joints

Horses recovering from joint conditions also require nutritional support to maintain healthy joints and cartilage.

Meeting vitamin and mineral requirements is the first step in supporting joint health. [7] In particular, trace minerals are integral for the synthesis and maintenance of connective tissue.

In horses and other animals, research shows that feeding adequate trace minerals helps with regulating inflammation, as well as improving lameness and joint lesions. In addition, research shows that organic trace minerals are superior for supporting joint health compared with inorganic sources. [9][10]

Mad Barn’s Omneity is a balanced vitamin and mineral supplement that is suitable for all horses. It contains 100% organic trace minerals, which have superior bioavailability to support the needs of horses with joint health issues.

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In addition to meeting trace mineral requirements, nutritional supplements containing docosahexaenoic acid (DHA) and methylsulfonylmethane (MSM) can help maintain joint health in horses.

DHA is an essential omega-3 fatty acid that has been shown to support regulation of inflammation in the joints of arthritic horses. [11] Mad Barn’s W-3 oil is a fat supplement that contains DHA from microalgae, along with natural vitamin E to support immune function and antioxidant defenses.

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  • Promotes joint comfort
  • Helps to fight inflammation
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MSM is a readily available form of the mineral sulfur that is important for the formation of collagen and glucosamine, which are essential for healthy cartilage and connective tissues. MSM also has antioxidant properties and has been shown to provide a protective effect in the joints of performance horses. [12]

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Prognosis

The prognosis for a horse with bog spavin depends on the underlying cause and the severity of the case.

In mild cases without significant underlying joint disease, the prognosis is typically good, and the horse can return to normal activity following appropriate treatment and rest. [6]

In more serious or chronic cases, especially those resulting from an injury or underlying conditions like osteoarthritis or osteochondrosis, the prognosis can vary. The outcome depends on the specific cause, how well the horse responds to treatment, and compliance with stall rest recommendations. [6]

In the most serious cases, such as when the horse develops articular sepsis, the prognosis is guarded. [6]

Prevention

Prevention of bog spavin is challenging due to the number of potential underlying causes. To minimize the risk, it is recommended to protect horses from injuries, provide adequate rest, feed a high-quality forage-based diet, and feed a vitamin and mineral supplement to prevent nutritional deficiencies.

To prevent septic arthritis, all wounds near the tarsocrural joint must be kept clean and dry. [4] In cases of deep or non-healing wounds, veterinary assistance may be required to change bandages. Further investigation and medical intervention may be needed to support healing.

Summary

Bog spavin in horses describes accumulation of fluid in the hock joint as a result of inflammation in the joint between the tibia and the tarsal bone. It is generally associated with other connective tissue or joint diseases.

  • Horses of all ages, sexes, and breeds are at risk, but performance horses and those that are obese or in heavy work have an increased risk.
  • The primary symptom of bog spavin is a characteristic ring of swellings that protrude from the joint; in some cases lameness may also be present.
  • Diagnosis is based on the characteristic appearance of the joint along with diagnostic imaging.
  • Treatment for mild cases includes rest and anti-inflammatory drugs.
  • More severe cases require injection of corticosteroids, bandaging, anticholinergic drugs, and fluid drainage.
  • In the most severe cases, hospitalization is required.

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References

  1. Baxter, G. M., Ed., Adams and Stashak’s Lameness in Horses. Seventh edition. Wiley-Blackwell, Hoboken, NJ. 2020.
  2. Pothiappan, P. et al., Bog Spavin and Its Management in a Kathiawari Horse. Intas Polivet. 2012.
  3. Dar, K. et al., Bog Spavin and Its Management in a Local Horse of Kashmir—a Case Report. SOJ Veterinary Sciences. 2016.
  4. Clegg, P., Conditions of the Equine Tarsal Joints. Companion Animal. 2006.
  5. Weaver, M. P. and Wilant, L., Owner Survey of Tarsocrural Effusion (Bog Spavin) in Clydesdale Horses. Veterinary Record. 2012.
  6. Ross, M. W. and Dyson, S. J., Diagnosis and Management of Lameness in the Horse. 2nd ed. Elsevier Saunders, St. Louis, Mo. 2011.
  7. Guoyong, L. et al., The Impact of Trace Elements on Osteoarthritis. Front. Med. 2021.
  8. National Research Council. Chapter 5: Minerals. Nutrient Requirements of Horses. 2007.
  9. Zhao, XJ. et al., Oxidative Stress and Imbalance of Mineral Metabolism Contribute to Lameness in Dairy Cows. Biol. Trace Elem. Res. 2014.
  10. Sirri, F. et al., Effect of Different Levels of Dietary Zinc, Manganese, and Copper from Organic or Inorganic Sources on Performance, Bacterial Chondronecrosis, Intramuscular Collagen Characteristics, and Occurrence of Meat Quality Defects of Broiler Chickens. Poultry Science. 2016.
  11. Manhart, D. R. et al., Markers of Inflammation in Arthritic Horses Fed Omega-3 Fatty Acids. The Professional Animal Scientist. 2009.
  12. Marañón, G. et al., The Effect of Methyl Sulphonyl Methane Supplementation on Biomarkers of Oxidative Stress in Sport Horses Following Jumping Exercise. Acta Vet. Scand. 2008.