Silver Honey Rapid Hoof Care Thrush Foam is the first and only thrush treatment to combine Manuka Honey and MicroSilver BG. | Photo Courtesy Silver HoneyThrush might seem like a minor hoof issue but, left unchecked, it can negatively affect a horses comfort, soundness, and overall hoof health. We spoke with Amy Santonastaso, VMD, MS, Dipl. ABVP (Equine), clinical assistant professor at the Virginia-Maryland College of Veterinary Medicine in Blacksburg, Virginia, to learn how this common condition develops, what makes some horses more susceptible, and how early intervention through teamwork can make all the difference.TH: How do you define thrush, and what organisms usually cause it?AS: The medical name for thrush is equine nonproliferative pododermatitis of the frog. Essentially, its a superficial infection of the frog that causes degeneration and a black discharge familiar to many horse owners. Its generally thought to be caused by bacterial invasion, though it likely involves multiple contributing factors that come together to allow thrush to develop. We dont know exactly which bacteria are responsible, but they are believed to be anaerobic bacteriaorganisms that thrive in environments without oxygenthat invade when the frog is compromised for some reason.TH: What hoof shapes, conformation characteristics, or management practices make horses more prone to thrush?AS: Environment can play a crucial role in the development of thrush. Horses kept in moist environments with a lot of organic debris, such as manure or urine, are especially at risk. This is partly because these conditions promote the growth of anaerobic bacteria, but also because they contribute to the breakdown of a healthy frog. Horses whose feet arent picked regularly or that live in environments where dirt and debris can continuously pack into the sulci on either side of the frog could develop thrush.Horses that already have an abnormal frogwhether due to conformation, trimming, or shoeingare also predisposed. For example, horses that partially shed their frog, allowing dirt and debris to collect underneath flaps of the partially shed tissue, create prime conditions for bacterial growth.Horses with small, underdeveloped frogs might also be predisposed, as are those with club feet or sheared heels.TH: What early signs of thrush should horse owners watch for, and how can they tell the difference between normal frog shedding and tissue loss from thrush?AS: The classic sign of thrush is a thick, black, often foul-smelling discharge in the sulci of the frog. Its normal for horses to shed their frog and, when they do, the farrier will typically pare away the separated pieces to help dirt and debris fall away more easily. Horse owners should pay close attention to every nook and cranny of the hoof, regularly examining and cleaning these areas.If a moist appearance developsespecially when accompanied by thick, black dischargeits time to involve both the veterinarian and farrier to prevent thrush from becoming more widespread. Caretakers should also be alert for any changes in the frogs shape, particularly if it appears to be getting smaller, or if the horse shows pain when picking out the feet. These red flags indicate needed intervention.Silver Honey Rapid Hoof Care Thrush Foam delivers powerful, natural antimicrobial action in an innovative expanding foam. | Photo Courtesy Silver HoneyTH: Why do horse owners need to address thrush promptly? What kinds of problems can it cause if left untreated?AS: Severe cases of untreated thrush can lead to several complications. Early thrush is generally limited to the most superficial layers of the skin covering the frog but, when unaddressed, the infection can invade deeper tissues and cause more serious problems. Early thrush is not typically painful, but deeper infection can lead to pain and lameness.Thrush also destroys frog tissue, causing the structure to become smaller and less functional. While this might not seem like a major concern at first, a healthy hoof relies on a well-developed frog for normal function, including proper blood circulation throughout the hoof and shock absorption when the foot strikes the ground.TH: How does thrush affect the overall health and function of the hoof?AS: Thrush can be a bit of a chicken-or-egg situation because a frog that becomes smaller and weaker for other reasons can, in turn, make it easier for thrush to develop. Either way, as thrush leads to atrophy and destroys healthy frog tissue, it can alter the way the entire hoof functions.Normally, the wedge-shaped frog occupies most of the space between the heels in the back part of the foot. This structure should contact the ground and, again, helps absorb shock. This helps dampen the vibration transmitted through the leg, reducing wear and tear on the limb during movement. Thrushs effects on the frog reduce or even eliminate this shock-absorbing ability. Additionally, if the frog no longer contributes to weight-bearing, more of the load shifts to the hoof wall alone, which can lead to issues within the rest of the hoof capsule.The loading and unloading of the frog and sole also play an important role in maintaining blood flow to all the tissues within the foot. An underdeveloped frog can reduce circulation to parts of the foot, potentially leading to other pathologies.TH: What common mistakes do you see owners make when they try to treat thrush on their own, without farrier or veterinarian input or oversight?AS: There seem to be two common problems when it comes to treating thrush. The first is that treatment isnt aggressive enough, or all the contributing factors arent addressed. This allows the infection to smolder without ever fully resolving. In these cases caretakers often find themselves constantly battling thrush, with every small insult to the frog triggering another flare-up.The second common problem is using treatments that are too aggressive. Some products can make the situation worse by damaging the outermost layer of the frog, creating a scablike barrier over the deeper tissues. This can make it appear as though the thrush has resolved, but it creates an even better environment for trapped anaerobic bacteria to thrive. If the treatment damages the frog tissue, it opens up more areas for bacteria to invade, allowing the infection to worsen and spread.TH: How much do factors such as stall cleanliness, turnout conditions, and moisture levels really influence a horses risk of thrush?AS: Thrush is a multifactorial disease, but environmental conditions almost always play a key role in its development. Constant moisture and, again, the presence of organic debris create the perfect breeding ground for many types of bacteria, including those that cause thrush. The heavier the bacterial load in the environment, the more likely these microbes will come into contact with small injuries or compromises in the frog, establishing infection and causing disease.TH: What role does good trimming and frog maintenance play in preventing thrush?AS: Good trimming and frog maintenance is at least as important as the environment in preventing thrush. Regular, thorough trimming of the frog reduces the presence of crevices where the bacteria like to hide. Youre also allowing better visualization of the frog and the sulci on either side, which will help you notice early signs of disease more quickly. Also, proper trimming of the whole foot, and especially the frog, promotes normal function of the foot, resulting in the whole hoof capsule being healthier and more resistant to disease.TH: When do you recommend using topical or systemic antimicrobials to treat thrush, and when do you consider it unnecessary or even harmful?AS: When thrush progresses to the point deeper tissues are involved, systemic or topical antimicrobials might be necessary. At this stage the infection could spread further, and the severity of the disease often prevents healing through environmental and husbandry changes alone. In general, I try not to overuse topical or systemic antimicrobials to treat thrush. In some cases, thrush can often be effectively managed through environmental changes and the use of topical antiseptics without needing to resort to antimicrobials. Its important to remember that antimicrobial resistance is a growing concern, so we should reserve these treatments for cases where theyre truly necessary.Additionally, if we use antimicrobials without addressing the horses environment and management, the infection might temporarily improve but will likely return. Continued exposure to the same bacteria increases the risk of these microbes developing resistance to the antimicrobials being used. In the case of systemic antibiotics, they circulate through the bloodstream but, since the outer layers of the frog (where the infection begins) lack a direct blood supply, systemic antimicrobials will not effectively reach the infection site.TH: Why should horse owners think about antimicrobial resistance, even when theyre just managing thrush?AS: Antimicrobial resistance is becoming an increasingly serious problem. It takes a long time to develop new antimicrobials, and bacterial resistance sometimes outpaces our ability to create new medications to treat these infections. Every time we use an antimicrobial, for any reason, we run the risk of bacteria developing resistance to it. For this reason we should reserve antimicrobial use for situations where no other effective treatment options remain.It might be difficult to relate treating a case of thrush in a horse to doctors treating a hospitalized person battling a severe bacterial infection that no longer responds to antibiotics, but the connection exists. Each time antimicrobials are introduced into the environment, even nontarget bacteria are exposed, contributing to the broader problem of antimicrobial resistance.TH: Does it ever make sense to test or culture a foot with thrush to figure out the cause of the infection?AS: Culturing anything on the bottom of the foot can be a tricky situation. In most cases it is unrewarding because we expect the foot to be exposed to lots of different bacteria from the environment, so we will probably get a big mix of bacteria on the culture and none of them might actually cause the disease. However, in some cases, if you can get a sample from a deeper tract it could be more protected from the environment. In addition, if the culture grows so much of one particular bacterium that it overwhelms the other bacteria in the sample, you can make a good guess that this is the cause of the infection. However, in most cases we wont get meaningful results from a culture on the foot so we often elect not to do it, at least early on.TH: How can owners, farriers, and veterinarians work together to prevent and treat thrush, while avoiding overuse of antimicrobials?AS: When all three of us are on the same page about the care of the horse, we can make sure we catch problems as early as possible, maximizing our ability to treat them without reaching for antimicrobials. Good regular trims by a farrier give us the best hoof health to prevent thrush development. Having the experienced eye of the farrier on the foot will often result in earlier identification of thrush or risk factors before it even develops. The owner maintaining good hoof hygiene practices day to day and monitoring for early signs of problems will also help prevent the disease from occurring or at least from letting a small problem become a big one. Your veterinarian can help determine which treatments are called for in any given situation and can also contribute to keeping the rest of the horse healthy, which can only help.