In Eastern Canada, spring is the dreaded season for thrush. The extremely wet conditions along with rich grass make it very likely to occur. The problems caused by thrush usually interfere with getting the horse back to work before the show season.
What is thrush?
Thrush is the generic name given to a bacterial and/or fungal infection of the frog. When left untreated, it can work its way to the frog corium (inside the hoof capsule).
An affected frog will have a strong and distinctive smell. Thrush can affect the whole surface of the frog (like on the picture) or penetrate the lacteral and/or central sulci. One foot can be more affected than the others.
It can be very painful to the horse. Some of them will even show a pain reaction to thumb pressure. A horse in this situation will do everything to avoid putting weight on the back of its foot. As a result, the horse's stance, locomotion and general well-being will be greatly affected.
Thrush is more likely to happen when the horse spends a lot of time on wet and soiled ground (mud, dirty stalls, etc.), especially when they are standing a lot.
It is more frequent in horses that:
- Have metabolic issues (Cushing's, insulin resistance, etc.),
- Are laminitic/have foundered before,
- Are not getting a balanced diet (minerals play a key role in hoof health),
- Have a weak frog (either by lack of movement or excessive trimming).
As mentioned above, thrush can cause serious pain. Horses will try to relieve the pain when standing by keeping their knee slightly bend in order to minimize pressure on the back of their foot. It is worse on hard footing such as concrete. You can also observe the horse; in some cases the leg seems to shiver slightly.
To make sure that it is a posture, not a conformation flaw, you can gently push the back of the knee forward. If it bends right away/ abruptly, it is a posture problem. If the horse is very stable, it is conformation.
This stance will strain the leg muscles, tendons and ligaments as they are constantly working to stabilize the leg. Stiffness in the shoulder will occur as a result of this abnormal posture.
If the situation goes on untreated for several months, more generalized issues will appear and soundness will be affected.
The hoof will also grow abnormally due to protective mechanisms. It will contract and grow longer heels in order to lift the sore area off the ground. This will affect joint angles, ligaments, tendons, and more generally soundness. Excessively trimming the heels down will just make the horse more tender footed. This is why thrush should be addressed before the hoof starts distorting.
NB: caudal foot pain (pain in the back of the foot) can have a variety of causes. If your horse stands this way but has perfectly healthy frogs, consult with your veterinarian.
Consequences: in motion
As mentioned above, the horse will do everything it can to avoid putting pressure on its painful frog. When you think of the weight of a horse and the really small size of its foot in relation to this weight, you easily understand why.
In motion, it will land on its toes instead of landing heel first. This will cause abnormal biomechanics of not only the hoof but also the whole leg. Landing toe first for a long period of time will:
- Tear the laminae apart (think of the laminae as velcro, with one part being pushed down),
- Damage the deep digital flexor tendon,
- On a longer term, the navicular bone,
- Bone remodeling can even result from the repetitive concussions at the tip of P3,
- Cause excessive strain on the lower leg's ligaments and tendons.
I hope that by now you are realizing the possibly dire consequences of something as common as thrush.
Toe-first landing isn't always easy to spot for an untrained eye. If you are unsure, there are signs that your horse may be landing toe first:
- Excessive wear at the toe (and lateral and medial flaring)
- Toe cracks (which will be come a point of entry
- Short strides, stiffness (the leg never fully extends)
- Unwillingness to go forward
- Frequent stumbling
NB: this is another reason why a good hoof care practitioner will always
watch the horse move before and after trimming/shoeing.
NB2: as mentioned above, the cause for toe-first landing may not be thrush, or not thrush only. However, if there is both thrush and toe-first landing, address the thrush and if movement improves, you will know that it was the problem. If it does not, consult with your veterinarian.
The reason I mention prevention before I mention treatment is because a healthy hoof living in a healthy environment will not be affected by thrush. Allow your horse to move as much as possible (turnout and exercise) in order to stimulate the development of the digital cushion, hoof growth and callusing of the frog. It will also encourage musculo-skeletal health, therefore allowing proper biomechanics.
Ensure that your horse gets a balanced diet, in particular regarding minerals that play a key role in hoof health. If your horse has metabolic issues, a carefully tailored diet will also be of great help with its condition.
Finally, a dry environment is ideal. However every paddock gets muddy in the fall and in the spring. If you can keep shelters and feeders on higher grounds/drier, it will already be helpful. To avoid proliferation of bacteria, pick up manure as often as possible. Keep stalls clean and with sufficient bedding.
NB: if your horse is unsound, forcing them to exercise will likely worsen compensation issues and slow down the recovery process. If you can't make your horse comfortable (with padded boots for example), let them rest until they can move soundly. Rest doesn't mean stall confinement though, they can be turned out (providing the conditions are relatively dry).
Most commercial thrush treatments are very aggressive. As a result, they damage both affected and healthy tissue, making the frog more fragile and more likely to suffer from thrush. Yes, it is a vicious circle!
Depending on how busy you are, there are a few options. Soaking the hooves in a mix of water and apple cider vinegar 3-4 times for 20-30 minutes a week is one of them (make sure the feet are cleaned beforehand).
If you can't commit to that, there are products like Clean Trax and White lightning that are both efficient and non damaging for the healthy tissue. I have used White lightning many times and I am still amazed by the results. In one application, the hoof changes colour and is much drier. Several applications can be needed in heavy cases.
Another topical treatment: a 50/50 blend of athlete's foot cream and triple antibiotic ointment (with analgesic) that you will syringe in the clefts. It can be used every day until thrush disappears. I also heard that topical mastitis treatments (for cows) is very efficient.
If your horse is really sore, using padded boots will keep them comfortable when moving. Using diapers in the boots (changed twice daily) will keep the feet dry.
The digital cushion: a virtuous circle?
The digital cushion is a very important supporting structure of the equine hoof. It is originally made of myxoid and fibrous tissue. Movement will stimulate the digital cushion; it will adapt and become fibrocartilage, a strong and supportive tissue. A well-developed digital cushion will protect and support the caudal/navicular part of the hoof, enabling proper locomotion and lasting soundness. On the other hand, an under-developed digital
cushion due to lack of stimulation (because of
lack of movement or of toe-first landing) will weaken the back of the foot and increase the risk
of injury and unsoundness.
You see how a painful frog would have an impact on the health of the digital cushion and more generally soundness.
As usual, we need to look at the whole picture. Thrush may happen in the frog but it will affect the hoof's biomechanics, muscles, ligaments and tendons, performance, and on the long term soundness and well-being.
I hope you found this post interesting, and that you will now look at thrush differently. Thank you for your visit!