HEALTHY FROG, HAPPY HORSE
The triangular pad of tissue at the center of the equine hoof has many functions and often signals when something is amiss.
Picking out hooves is one of the simplest horse-care tasks. You probably do it automatically by now---the movements of lifting a hoof and running a pick through its contours are ingrained in your muscle memory as deeply as tying your own shoes. But this routine chore is also one of the most important when it comes to keeping your horse sound.
Not only does picking remove potentially injurious debris from your horse’s hooves, but it provides the perfect opportunity to spot potential problems before they cause trouble. You may notice a loose shoe, for example, or discover odors, discoloration or other signs of bacterial or fungal infection. Taking a moment to inspect
the underside of a horse’s hoof after you’ve picked it clean is time well spent. A focal point of your investigation will be the hoof’s frog, a triangular pad of tissue on the bottom of the foot.
In addition to being a distinct visual landmark in the hoof, the frog serves important---but still somewhat mysterious---functions. In addition to acting as a shock absorber, the frog is thought to aid in traction. Contrary to popular belief, the frog does not act as a pump that sends blood back up to the heart; however, it may play a role in a complex hydraulic system within the foot. It contains scent glands, as well as important sensory nerve endings that assist the horse in navigating his environment.
Here’s a quick look at this fascinating structure and the troubles it can develop.
SHAPED BY ITS SURROUNDINGS
The appearance of the frog can tell you a lot about the condition of the hoof itself.
A typical frog appears broad and flat, with clefts---called sulci---along each side, and a central cleft that looks like a wide impression of a finger rather than a deep groove. The frog has a higher moisture content than the other structures in the hoof, giving it the feeling of firm rubber.
The frog takes on different characteristics depending on the moisture content of the horse’s environment and the conformation of the foot. Wet or damp living conditions will make a frog softer and more pliable than one exposed to an arid climate. Likewise, a narrow foot or one with contracted heels generally will have a correspondingly narrow frog with deep collateral grooves. A flatter foot will likely have a wider frog and shallow grooves.
The frog’s shape influences the amount of debris that gets caught in the hoof’s clefts. Regular, conservative trimming of the frog can help prevent infection and disease by removing dead tissue that can trap dirt and bacteria. Ground contact also affects the frog’s appearance. When the frog comes in contact with the ground as a horse stands or moves, dead tissue sloughs off. Hoof pads can slow this process.
The natural process of shedding dead tissue may leave a frog looking a little craggy at different times of the year. Nonetheless, a ragged appearance accompanied by a foul smell or discharge can suggest a problem with the hoof.
TROUBLE AFOOT
Thrush and canker are two of the most common conditions that affect the hoof.
Thrush is caused by a combination of different bacteria, but commonly associated with Fusobacterium necrophorum. This infection is know for its strong, unpleasant odor, black and moist discharge and signs of tissue degradation. Thrush can give the frog a rough looking appearance and abnormal shape.
While mild thrush doesn’t typically cause lameness, if the infection invades the deeper soft tissues the result may be increased sensitivity and pain. In some horses, bacteria invades the space between the heel bulbs and establishes a secondary infection. Thrush is usually confined to the collateral sulci of the frog but in severe cases the sole may be affected as well.
Although much less common than thrush, canker is often confused with that condition because in its early stages it can have a similar appearance and produces unpleasant odors. However, a significant difference between the two conditions is that thrush erodes or destroys tissue, while canker causes mounding overgrowths of tissue.
Canker is characterized by a white, cheesy appearance and the tissues become filamentous (finger-like) in appearance. Canker causes the horn growth of the frog to become crumbly and the infected area to be sensitive to the touch. The affected tissues bleed easily when disrupted. Some canker lesions are small---about the size of a dime---while others can become extensive, affecting large regions of the hoof capsule and invading deeper tissues.
Canker can become severe enough to cause lameness and may extend to the sole, bars, heel bulbs and other parts of the hoof. Historically, canker has most often been seen in draft horses, but any horse can develop this condition. The cause is unknown, but papillomavirus or spirochete-type bacteria have been implicated.
Unsanitary living conditions are often blamed for cases of thrush or canker and they can indeed make these conditions more likely or more severe. Lack of exercise, overgrown hooves and contracted heels can also make horses more susceptible to thrush or canker. But even well-kept horses under ideal management conditions can develop these hoof conditions.
Bacteria have been implicated in both canker and thrush. Yet antibacterial treatments alone do not always resolve these problems so it is likely that the organisms contribute to these conditions but are only part of the root cause.
Canker is found throughout the United States but is most often seen in the southeastern United States. In contrast, thrush is much more pervasive throughout the country.