White Line Abscesses of the Equine Hoof

By Pat Wagner, Hoof Rehabilitation Practitioner

Hoof abscesses are the most misunderstood, misdiagnosed, mistreated and the most common cause of lameness for equines.  Consequently there is almost no correct information online about this very common hoof condition.

Proper treatment is delayed because hoof abscesses are so often improperly diagnosed, which leads to sometimes devastating decisions for the afflicted equines.  If you are involved with horses, it is your responsibility to learn how to identify a hoof abscess, the common causes of hoof abscesses, the symptoms, treatments, and how hoof abscesses affect the hoof.  This article is meant to shed new light and bust a few myths about this painful condition as well as provide information on how to reduce the pain and help with recovery during the process..

Both Shod and Unshod Horses are at Risk
Chronic abscessing of the bars or wall is generally caused by incorrect trimming or neglect.  Whether a horse is shod or unshod has almost no bearing on whether a horse is having issues with WL abscesses except for the fact that a shod hoof is often a hoof that has been trimmed incorrectly.  A shod hoof must be trimmed to support a shoe and that type of trimming cannot allow the hoof to be trimmed as it would be worn in nature. 

Cracks like you see in the above photos are often mistaken for injuries to the hoof even by some of the most well respected experts in the equine medical field.   However, what is seen here are abscess rupture sites about 3 months after eruption at coronet band. As the wall grows toward the ground, the rupture site is migrated closer to the ground with the wall growth.  Above the crack new wall growth comes in with healthy new connective tissue (lamina) while disconnected wall below the site will likely snap off due to leverage from impacting the ground, and is not a cause for concern because the laminitic connection behind the wall (below the rupture site) is no longer a viable connection - it's dead.  Correcting our trimming to reduce flare will keep wall abscesses from reoccurring. 

A rupture at the front of the hoof hours after erupting.  This is a draft hoof. 

At right: A bar abscess that has affected the entire solar papillae.  (Typically termed "subsolar abscess") New sole growth is taking place now.  This pregnant mare was lame in shoes and mistakenly diagnosed as a founder case by her vet and euthanized by her owner in the prime of her life. Due to an abscess!
Bar abscesses as mentioned above can and often will affect areas of solar papillae.  Solar papillae is the connective tissue between the third phalanges (P3 or Coffin Bone) and the hoof sole.

This type of abscess can be incredibly painful and can reside beneath the surface of the sole for months or years and is usually the type of abscess that invades the neglected or shod hoof. 

Sub-solar abscesses are often misdiagnosed as founder because the symptoms appear to be the same.

To learn the trimming methods that will help your horses avoid crippling hoof absesses, please see our DVD: Discovering Your Horse's Natural Hooves - How to Trim the Barefoot Horse.

Patricia Morgan Wagner, Hoof Rehabilitation Practitioner has devoted her career to the research of White Line Hoof Abscesses and education of horse owners and hoof care professionals on this important topic.  She believes that long standing ignorance regarding the cause and process of this common hoof ailment has cost too many horses their lives; when correct recognition, proper hoof management and time could save have saved most of them.  Patricia's hope is that this information can help you reduce the risk hoof abscesses as well as recognize and rehabilitate ailing hooves successfully.
White Line Abscesses that affect the hoof bars are somewhat different than the WL abscesses that affect the lamina between the coffin bone and the outer wall.  WL-Bar abscesses always rupture at the heel bulb (soft tissue). However, due to the relationship of the bars to the sole, WL Bar abscesses  can affect the connective tissue (Solar Papillae) of the entire sole. Varying degrees of solar papillae is affected from small areas near the bar on the invaded side of the hoof, to the entire solar area.
At left: The WL abscess rupture site is at soft tissue of the heel bulb.  It's likely that the entire solar area has been affected by the abscess and will slough while new sole material is being regeneration underneath the dead sole.  This creates a blistering affect with debris and pus between the two layers.  Scrapping into this debris field causes some to assume that abscess is wherever they happened to dig into the sole and was caused by a stone bruise, when in fact, we can always track it back to the originally affected bar.
Entered here
An interesting technique used by a vet to drain the abscess track, just as the abscess is about to rupture, offering the horse instant pain relief. Note: this picture was taken weeks after the abscess erupted which is why we see wall growth above the site.  This technique offers relief when performed close to the time of rupture.

Hooves trimmed like this are more likely to suffer a wall abscess in the area of the toe.

Above: at this stage, the abscess has invaded the whiteline at the solar level, tracked up and has is just rupturing.  This is typically when the horse feels the most pain, then relieve!

Left: This track is growing down with new wall growth, but a second abscess followed up the same track causing 2 ruptures in same track.  At this stage the horse is typically no longer feeling pain.
Right: the flare that is the initial cause of the WL separation that leads to abscess is seen here as the abscess track is nearly grown out.  Yes, this hoof is set up to be re-affected.
Same hoof in different stages of abscess. 
Subsolar abscess
The bar is the less obvious location where abscesses can start.  The abscess that enters in the white line of the bar makes it assent up the area of whiteline through the back of the hoof tracking toward soft tissue where it will rupture in the heel bulb.  Bar abscesses are often missed, because our attention, when searching for causes of lameness is rarely  drawn to the area of the heel bulb and the hair in the back of the hoof often obscures the rupture until it starts to grow down the heel where it is then mistaken for a wound caused by forging other some other cause.  Therefore, bar abscess are most often diagnosed as a mystery lameness.  The pocket left by the abscess in the bar can be re-infected several times, which can be baffling to professionals who do not understand the anatomy of the hoof and the cause of bar abscessing.

Causes of WL Hoof Abscesses
Flare caused by neglect or incorrect trimming is the leading cause of abscesses. Flare typically leads to stretching of the white line.  If flare is not corrected it leads to separation of the white line allowing an entrance site for dirt, manure, urine (debris) to infect the lamina and that infection begins an assent up the laminate between the hoof wall and the coffin bone (leaving a trail of dead connective tissue in its wake) and erupting when it arrives at soft tissue - the coronet band or the heel bulb depending on whether the abscess entered at the white line of the outer hoof wall or the white line of the bar.  The swelling and eventual eruption at the coronet band (soft tissue) that is the part of the process when the horse feels the highest degree of pain and usually becomes lame prior to rupture.  Once rupture takes place, the horse will gradually become sound again.
Shod hooves that are likely to suffer abscesses as the hoof transitions from shod to barefoot.  Abscesses are mistakenly considered a detoxification process of an shod hoof to a healthier bare hoof.  But that is only true in the sense that abscesses may fester in the hoof longer when a shoe is attached to the hoof and deshoeing, plus corrective trimming allows the abscesses to finally migrate to soft tissue where it can rupture. 
Neglected hooves frequently suffer from abscesses for obvious reasons.  The hoof will either grow vertically or horizontally in extreme cases of mismanagement, or neglect and either condition will open the connective tissues up tot he outside world allowing elements to invade the lamina. 
Diet imbalances are thought to be a serious factor in causing equines to chronically abscess, and while it's true that the hoof wall of horses who lack proper nutrition may not be as dense or strong as a horse on a healthy diet, the more likely cause of poor diet being a direct factor in unhealthy hooves is that poorly fed horses generally also do not receive regular and correct hoof maintenance causing flared walls that lead to stretching and separation of the white lines, thus allowing elements to invade the WL that cause destruction of the connective tissue.

Bar abscesses often become a chronic problem because the trimming strategies do not change.  The bars will become re-infected over and over and in more than one hoof, due to the fact that whatever hoof-care one hoof is receiving, all four hooves suffer with that same lack of correct hoof care.  So lameness can be seen, off and on, in all four hooves.
Bar abscess often affect the entire solar papillae.  This is an important consideration and that type of abscess is often referred to as a sub-solar abscess further explained below.  The bars of the hoof must be trimmed along with the wall because the bars ARE an extension of the wall.  If the bars are not tended to in the same manner as the wall, then they will cause pain and or begin the abscess process.  My hope is that it becomes common practice to trim bars (not take them completely down to the sole plane) but simply trim bars as we do the walls. (See pictures below.)

Hoof Abscesses Are Often Misdiagnosed. Horses suffering from an abscess (or multiple abscesses) may not exhibit pain/lameness. However, typically abscesses are an extremely painful process. Symptoms displayed by the horse are often misdiagnosed as founder, navicular, or other “mystery lameness” such as stone bruising which in my opinion isn't a logical cause for lameness.
Many suffering horses are started down a traditional path of “corrective” shoeing (which more often than not is done to correct the hoof ailments caused by the shoes in the first place) and eventually put down.
Because bar abscesses can go completely undetected or are often misdiagnosed as a mystery lameness, it’s difficult to say how many horses have been euthanized when correct trimming could have resolved the problems.

How do you know if your horse is in the beginning stages of abscess?  Observation of our herd has taught me that pain is pain to horses and the signs may be same no matter where in their bodies the pain is originating.  When we see a horse who is clearly showing symptoms of colic, the next day, an abscess erupts and the horse is feeling much better.  So symptoms of colic: obvious distress, loss of appetite, getting up and down, and repetitious rolling, may actually be symptoms of the onset of an abscess eruption.  But usually the first sign of hoof abscess pain is lameness on one leg. There may or may not be unusual heat, or swelling.  Some horses may want to lay down through the entire event.  Others may only show slight lameness and only when being ridden.  It just depends on which hoof is involved and how much of the hoof is involved in abscess.  Several abscesses can erupt at the same time in one hoof.

Relieving the Pain of Hoof Abscesses. Booting the horse to give it relief from the pain of an abscess, as it is surfacing, is beneficial, but may slow the the process of eruption, so time out of the boots is critical for healing.   We use he Soft Ride Comfort Boots; or the Trail boots by Easycare, Inc.
The traditionally treatment of cutting away a large part of the sole or frog and applying bandaging and leaving the horse in a stall for extended periods is not conducive to healing.  Digging with sharp tools into an abscessing hoof only creates an injury to an already ailing hoof. The abscessed hoof that we dig into will have one more issue to heal from and often the hole left by a veterinarian or farrier with the best of intentions is the injury that takes longer for the hoof to heal from than the initial abscess. 
Wait for the abscess to find its own way to the surface where it will rupture.  As stated above, the severe pain and lameness we generally observe during the abscess process happens just before the rupture at soft tissue.  Digging into the sole with the idea of finding a foreign object that may have (although rarely) invaded the hoof, or any attempts to cause the hoof to drain, only creates a secondary wound in the hoof. 
WL abscesses likely happen in the wild as well, and hooves heal from them without humans digging around in the hoof with their tools.  Simple powdered aspirin, which can be purchased in most feed retailers or online can have a significant positive affect on hoof pain.  Again, the highest degree of pain from a processing abscess is just prior to rupturing because the pocket of pus finally invades are area of lamina that is not stretched due to flare.  That is why abscesses rupture fairly predictably within days of noticeable lameness usually in one leg.

After a Hoof Abscess Erupts. Once the abscess has erupted and drained, allow movement at liberty (not forced) on soft ground.  treating the rupture site with something like Vetricin Spray, or scarlet oil spray, or antibacterial salves can help with healing.  But time and correct hoof maintenance are the main factors required to see the horse through to complete soundness again.  Keeping the hoof soft with long term booting and poultices, or soaking will delay the return to soundness.

How the Location of an Abscess Affects the Hoof. An abscess of the outer hoof wall erupts at the coronet band, but what is not commonly understood that the trail of dead connective tissue left in the wake of an abscess which tracks up the wall and exits at the coronet band no longer connects wall to bone inside the wall.  So as the rupture site grows to the ground with the new wall growth and very often the disconnect area of wall below the rupture site snap off due to leverage from the ground. Eventually the crack or rupture site itself will migrate to the ground where it can be trimmed off.  There is really no treatment that benefits the hoof at the point. This is just a natural progression of the hoof repairing itself.   (However, as the hoof grows out a "bar" abscess we see more than just a crack growing to the ground as you will learn.)
What Is a White Line Abscess?
A hoof abscess is a purulent inflammation of the connective tissues, lamina and solar papillae, where the pressure produced by the accumulation of pus between the dense structures of the hoof - hoof wall and bone - causes the horse extreme pain and is often, but not always, accompanied with swelling of the leg and noticeable lameness. 
Hoof abscesses enter at the bottom of the hoof, in the connective tissues of the hoof between the sole and the wall, the area termed "white line".  Abscesses can enter in one of two parts of the hoof.  In the white line of the hoofwall (where the wall connects to the sole) or the white line of the bar.  The bar is an extension of the hoof wall.

The whiteline of the outer hoofwall is the more obvious location where abscesses can start.  An abscess then takes the path of least resistance toward soft tissue where it ruptures at the coronet band.  As the hoofwall grows, we see the rupture site grow down with new wall growth.