Painful hoof abscesses in horses develop when bacterial or fungal organisms enter the hoof structure through a wound or opening and cause infection in the inner tissues.
The invading microorganisms and the ensuing immune response generate purulent exudate (pus) which causes pressure inside the hoof. This leads to pain, structural damage and lameness.
To prevent potentially permanent damage and suffering, hoof abscesses should be treated promptly.
Clinical examination including a lameness evaluation, the use of hoof testers, and radiographic imaging can aid in the diagnosis of the condition.
Abscesses are treated by promoting drainage of the exudate within the hoof and clearing the infection from it. Supporting hoof growth and a strong hoof structure is critical to regaining comfort and mobility.
What is a Hoof Abscess?
A common cause of sudden lameness, hoof abscess refers to an accumulation of discharging liquid (pus) that is produced by infected tissue within the foot of the horse.
Equine hoof abscesses develop beneath the sole of the hoof and behind the hoof wall. 
Hoof abscesses can develop if fungus or bacteria gain entrance through the hoof capsule (the epidermal layer) into the inner tissues of the hoof (the dermal layers).
Once inside the hoof, these microorganisms become trapped between the sensitive laminae (the tissue layer that bonds the hoof capsule to the coffin bone) and the hoof wall or sole and propagate. 
The microorganisms involved with hoof abscesses promote the accumulation of exudate (pus) behind the hoof wall or sole and cause an increase in pressure in the hoof capsule. The increased pressure causes the horse immense pain. 
Bacterial entry into the hoof capsule is made possible through a crack or break in the tissues of the hoof. Infectious organisms may penetrate the hoof in the following ways: 
- A defect or separation in the wall of the hoof
- A crack in the junction between the wall and the sole of the hoof
- A puncture wound on the solar surface of the hoof in the sole or frog
Hoof abscesses are very painful for affected horses and severe lameness can result very quickly.
If left untreated, abscesses can spread throughout the tissues within the hoof and compromise the podotrochlear apparatus, potentially resulting in permanent damage to the hoof and its internal structures. 
Causes of a Hoof Abscess
Microorganisms must gain entrance into the hoof capsule to initiate the development of an abscess. The most common ways microorganisms can enter the hoof capsule including the following: 
- Foreign objects such as nails, screws and glass can penetrate the hoof
- Horseshoe nails placed inside in the area where the hoof wall meets the sole (in the white line)
- Poor hoof quality due to genetic or environmental factors may compromise the integrity of the hoof
- Wet conditions caused by rainy weather or dirty stalls can cause the hoof to soften and become vulnerable to bacteria entering
- Brittle hooves caused by fluctuating moisture levels in the environment can promote cracked hooves
- Improper hoof management that causes flares or crushed heels can weaken the hoof structure and cause fissures
All horses can be affected by hoof abscesses. Hoof abscesses are most likely to occur during the wettest seasons of the year including the spring and winter, although they can occur at any time.
How a Hoof Abscess Develops
An abscess forms after foreign material has entered the hoof through an open fissure and subsequently migrated deeper into the structure to form a tract inside of it.
The pressure exerted on the hoof due to the weight of the horse promotes the migration of the microorganisms into the innermost dermal tissues.
The immune system initiates an inflammatory response inside the dermal tissues of the hoof capsule in response to foreign debris in this area.  As the invading microorganisms propagate in the tissue, inflammatory cells infiltrate the affected area.
The release of enzymes from the inflammatory cells and microorganisms promotes the death of cells in the tissues (necrosis) and the development of a grey/black colored exudate. 
The accumulation of exudate and the presence of inflammation in the tissue elicits a painful response in the horse because the hoof is unable to accommodate swelling.
A hoof abscess forms as the body responds to the infection in the affected tissues by sealing off the area with a thin layer of fibrous tissue. 
Clinical Signs of a Hoof Abscess
Hoof abscesses can cause a variable degree of discomfort in affected horses, although most horses experience a rapid onset of severe lameness. In the early stages of the abscess, lameness may be subtle but can later progress to a non-weight bearing state.
A hoof with an abscess within it will be warmer to the touch than the other hooves.
The affected foot will also have a digital pulse that is greater in intensity compared to the other hooves. The pulse is more noticeable on one side of the affected foot if the infection is localized to one side.
If a hoof abscess has worsened over time, it can cause inflammation and swelling that extends into the pastern and even further up the leg past the fetlock joint. The pastern or heel bulbs and the coronary band may also be swollen.
Diagnosing a Hoof Abscess
A veterinary exam including a lameness evaluation may be required to diagnose an abscess and rule out other types of injuries such as broken bones.
Symptoms of hoof abscesses are similar to symptoms of other conditions including severe sole bruising, laminitis, or a fractured coffin bone.
Hoof testers are a valuable tool for locating the focal area of pain in the foot of a horse with an abscess and for ruling out other causes of pain that extend over the entire foot. 
Using a pinching action, the hoof testers apply pressure over several spots on the hoof to determine if the horse is reactive.
A fissure or drain track may become evident after cleaning the hoof and removing old sole. However, in some horses affected by an abscess, the drain track is not visible.
If the drain track of an abscess cannot be located, x-rays (radiographs) may need to be taken to determine where it is. This form of imaging may help diagnose an abscess by indicating if accumulations of gas produced by the offending bacteria are present.
Infrared Thermography (IRT) has also proven to be a valuable tool for diagnosing hoof abscesses by measuring heat distribution within the hoof.
In a study of 66 horses, 10 of which had abscesses, researchers found that the latter group had hoof temperatures of 6.17 °C higher on average compared to the group of horses without abscesses. 
How to Treat a Hoof Abscess
Because hoof abscesses can be very painful for horses, some may benefit from analgesics (pain-relievers) to reduce their discomfort. Pain medications may be offered during the early part of treatment while the abscess is draining.
A veterinarian may prescribe bute (phenylbutazone), firocoxib, or banamine to control pain or swelling in severely affected horses. Antibiotics are not typically prescribed for equine hoof abscesses. 
Abscesses should always be treated as soon as possible to prevent extended suffering in affected horses. Treating an abscess promptly reduces the risk of the infection rupturing at the coronet band, a scenario that takes longer to treat and that can cause lasting damage to the foot. 
Infection due to an untreated abscess can potentially lead to laminitis. Once a horse develops laminitis, the horse may also become more vulnerable to abscesses. 
The most important factor in the successful treatment of a hoof abscess is ensuring the abscess has a drainage route. 
Establishing a Drainage Tract
An abscess with an obvious drainage track that is free of debris may be treated more easily than one without an established drainage route.
A veterinarian and/or farrier may for the treatment of abscesses where proper drainage is not present.
In some horses, the infection may be present deep within their hoof if it has migrated beneath the sole or further behind the wall away from the sole wall junction or white line. 
A veterinarian or farrier may need to establish drainage in a horizontal plane by using a small probe.
Caution must be taken to ensure no further damage to the hoof occurs if a drainage tract needs to be established.
An additional drainage tract should never be created in the sole adjacent to an existing tract as this could lead to problems including hemorrhage and infection in the coffin bone. 
Medicated Products and Poultices
Different types of medicated products can be used for treating hoof abscesses.
Ichthammol ointment is a traditional treatment derived from coal tar which is beneficial for its pain-relieving and mild antiseptic properties. 
This ointment is also helpful for drawing infection out of wounds on the hoof or other parts of the body.
Poultices and Wraps
A poultice can be used to draw infection from the drainage tract of hoof abscess.  Using a poultice helps to soften the hoof tissues and promotes drainage through an existing tract situated between the abscess and outer hoof wall.
Poultices are typically applied to an abscessed hoof for 24 to 48 hours at a time.  To maximize the efficacy of the poultice treatment, cover the entire foot including the coronet band.
Commercial medicated poultice pads can be purchased. The pad is used by immersing it in hot water, squeezing it out, and then attaching it to the foot with a bandage. A waterproof tape, diaper, or hoof boot should be used to cover the area and protect the hoof from microorganisms entering the drainage tract.
A “soak bandage” method may also be used.  This strategy involves wrapping the hoof in several layers of soft cotton material and placing Epsom salts inside the wrapping.
Over a period of 24 to 48 hours, the wrapped hoof is saturated in hot water multiple times.
Although soaking can encourage a hoof abscess to drain, oversoaking can weaken the structure and is potentially harmful. Follow your veterinarian’s advice as to how often to soak an abscessed hoof.
After the abscess begins to drain, the horse typically experiences rapid pain relief over 24 hours.  Until healing is complete, the hoof should remain bandaged.
An antiseptic treatment such as betadine or two percent iodine should be applied to the drainage tract. Medicated putty may also be used within the drainage tract to ensure microorganisms cannot re-enter the hoof.
Horses being treated for an abscess should be housed in a clean, dry area, such as a well-bedded stall or small paddock. Bandages should be removed and changed daily.
An abscess is considered healed after the drainage tract dries out and the affected tissues have healed over the opening of the tract. Only after abscess healing is complete and the affected horse becomes fully sound should shoes be applied to its hooves.
When to Seek Veterinary Advice
Consult with your veterinarian in the following cases if your horse develops a hoof abscess:
- A foreign object or nail has embedded itself in the hoof. Contact the veterinarian immediately so the hoof and the angle at which the foreign material entered it can be assessed
- If treating a hoof abscess that continues to drain for more than 48 hours
- The horse’s level of pain remains the same after the abscess has drained
- The horse refuses to eat during the process of treating the abscess
- Flesh begins to grow out of the drainage tract to the abscess
Typical Recovery Time
Horses with a mild infection due to a hoof abscess may be able to return to work in less than a week following treatment.
However, abscesses involving deep infections can take several weeks to resolve.
Abscess Recovery and Hoof Support
Full recovery from a hoof abscess requires regrowth of the hoof tissue to form a solid structure where the abscess created separation. This requires synthesis of the structural protein keratin, which is the most abundant protein in the hoof.
Optimal keratin synthesis relies on sufficient amino acid supply from the diet as well as several key nutrients, including biotin, zinc and copper.
Keratin, like all proteins, is made of amino acids. Ensure the diet is providing adequate levels of essential amino acids, in particular lysine, methionine and threonine
Vitamin B7 (biotin) is a co-factor for enzymes and contributes sulfur which is required for making keratin.
Several studies demonstrate that 15 – 20 mg of biotin per day is beneficial for supporting hoof hardness and increasing growth rate. 
Zinc and copper:
A proper balance of the microminerals zinc and copper supports keratin synthesis and provides antioxidant protection. It is recommended to provide these in their organic forms and in a 4:3:1 ratio of iron to zinc to copper in the total diet. 
There is anecdotal evidence suggesting the herb jiaogulan can support hoof health by increasing blood flow to the area. Jiaogulan contains gypenosides which activate nitric oxide synthase to increase nitric oxide production and blood flow.  
During the recovery period, increased blood flow can help deliver nutrients to the area and clear away waste to support tissue growth and repair.
In a case report, horses were given 1-2 grams of jiaogulan per 500 kg of body weight twice per day. They had better mental alertness and increased spontaneous movement.
Importantly, they returned to pasture soundness within 2 – 14 days and had improved lameness scores. 
Preventing Hoof Abscesses
Hoof abscesses are sometimes unavoidable, particularly if accidental penetration or injury is involved.
However, there are some steps you can take to decrease the risk:
- Ensure your horse’s environment is kept clean and dry. Maintain clean stalls and remove manure from paddocks on a regular basis
- Use a hoof hardener product to protect the hoof from damage caused by excess moisture during wet weather conditions. During dry weather conditions, use a product such as pine tar to help the hoof retain moisture
- Maintain your horse’s hooves on a regular farrier schedule to identify issues early and support healthy hoof structure
- Remove sharp objects including nails, pieces of metal, glass, or jagged rocks from your horse’s turnout area to reduce the risk of hoof injury
For guidance on formulating a hoof-healthy diet and supporting abscess recovery, submitting your horse’s diet and our nutritionists can provide you with a complementary consultation.
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