In this episode of the Disease Du Jour podcast, Stephen O’Grady, DVM, MRCVS, joined us to discuss thrush in horses, including the veterinarian’s role in recognizing and managing this condition and the structural defects in the hoof that lead to its development.
This episode of Disease Du Jour is brought to you by Bimeda.
Anatomy of the Frog
The hoof capsule comprises the hoof wall, sole, frog, and bulbs of the heel. These parts are all interrelated, O’Grady explained, and if one part is diseased, the entire hoof capsule becomes unhealthy.
The frog forms the palmar section of the horse’s foot and is closely related to the digital cushion above. Together, they support the back of the hoof, dissipate the energy of impact when the hoof strikes the ground, and aid in traction.
O’Grady explained that a healthy frog acts as an expansion joint between the heels. If the frog decreases in shape and mass, the digital cushion also decreases, and the heels begin to contract.
“When you have a good-sized, normal frog, and the heels of the hoof capsule and the frog are on the same horizontal plane, the horse’s foot has what they call a self-cleaning mechanism,” he said. “In other words, when the horse puts his foot down, the weight of the horse spreads the frog, and the frog pushes anything that’s in the sulci next to the frog out of there, so it keeps it clean.”
Etiology of Thrush
O’Grady explained that thrush is a degenerative disease that attacks the epidermal tissue and decreases its mass. It differs from canker, which is a proliferative disease.
Thrush occurs when the frog recedes below the surface of the hoof capsule, where it doesn’t get the stimulation it needs. Its epidermal covering then becomes more fragile and vulnerable to penetration. Over time, this area will pack with dirt, debris, and manure, which puts increased pressure on an unhealthy structure. Organisms begin to penetrate the epidermis, causing a low-grade infection that deteriorates the structures.
“If you have a horse with a healthy frog, you can put him in any kind of muck you want, any kind of surroundings, and he is not going to get thrush,” O’Grady said. “Because you have that surface area that is impenetrable because that structure is tough. Especially in a barefoot horse.”
How to Treat Thrush
Treating thrush involves keeping the hoof clean, applying medication, and packing it if there’s a fissure. “But that’s palliative in a way, because you still have a cause,” O’Grady said.
Proper farriery is necessary for managing a horse with thrush. O’Grady starts by looking at the position of the frog. If it isn’t aligned with the heels, it must be addressed.
In moderate cases, getting the heels and frog back on the same horizontal plane through farriery will make a big difference for the horse, O’Grady said, and medical treatments will further assist in treating the infection. For severe thrush cases, he often removes the horse’s shoes for a period to help strengthen the frog.
Advice for Collaborating With Farriers
“The vet-farrier relationship could always be improved,” O’Grady said. He advocated for mutual respect and reminded listeners that both parties bring skills to the table and are working for the betterment of the horse.
“When vets and farriers get together and they communicate, you wouldn’t believe what can be accomplished,” he said. “The veterinarian would say, ‘Hey, would you like radiographs?’ and the farrier would say, ‘Hey, would you mind radiographing so I can see whether I can drop this side more?’ This is where it comes together, and it’s really beneficial.”
O’Grady co-authored a paper on this topic, which you can read here.
Final Thoughts
In closing, O’Grady reiterated that you don’t find thrush in a healthy frog. “There has to be a mechanism to where that frog starts to lose mass, starts to deteriorate, where it can go ahead and acquire thrush,” he said. “There’s a cause behind thrush, and it’s not keeping your stall clean or how many times you can soak the horse’s hoof or put iodine in there. If you have a small, ribbon-thin frog that is quite receded down within the hoof capsule that’s diseased, it is not going to heal in that environment.”
About Dr. Stephen O’Grady
Stephen O’Grady, DVM, MRCVS, was a professional farrier for 10 years prior to obtaining his degree in veterinary medicine. He learned the farrier trade through a formal three-year apprenticeship under “Hall of Fame” farrier Joseph M. Pierce of West Chester, Pennsylvania. He then returned to school, attended Haverford College, and went on to graduate from the University of Pretoria, Faculty of Veterinary Science, in South Africa with a DVM degree in 1981. After graduating from veterinary school, O’Grady did an equine internship in Cape Town, South Africa. From here he went on to join Dr. Dan Flynn at the prestigious Georgetown Equine Hospital in Charlottesville, Virginia, where he stayed for 10 years before opening his own practice in Keswick, Virginia, devoted to treating competition horses and farriery.
In 2003, he opened Northern Virginia Equine in Marshall, Virginia, and in 2014, he moved back to Keswick, Virginia, and opened Virginia Therapeutic Farriery. Both are referral practices devoted to foot disease and equine therapeutic farriery. O’Grady combines his skills as a veterinarian and a farrier to better understand and treat problems of the foot. He has published 33 peer-reviewed papers in the veterinary literature, numerous papers in the farrier literature, written 18 book chapters, and edited two editions of Veterinary Clinics of North America on equine podiatry and therapeutic farriery, all resulting from his extensive work in equine podiatry.
In 2003, he was inducted into the International Equine Veterinarians Hall of Fame, and in 2009, he received the AAEP President’s Award for his work in farrier education. In 2019, he was awarded the coveted gold medal from the South African Veterinary Association. In 2020, he was acknowledged for his commitment to the education of equine practitioners around the world and received AAEP’s Distinguished Educator Award. In 2024, O’Grady was nominated and voted onto the AAEP Mentor Honor Wall.
Related Reading
- Thrush-Prone Horses: Building a Maintenance Plan for Clients
- White Line Disease in Horses
- Horses With Uneven Feet: Causes, Assessment, and Management
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