April 2003

Thrush: What is it?

In support of our mission statement for educational development, here is the another edition of Info Gaits

From "Adams' Lameness in Horses" Fifth Edition, Ted S. Stashak, pp.719: "Thrush, Etiology: Contributing factors for thrush are wet, unhygienic stable conditions, especially when horses stand in urine and manure-soiled bedding; neglect of daily foot care; and lack of exercise. Inadequate or improper trimming and shoeing, which promotes long contracted heels and deep sulci, appears to increase the risk of infection. Although no specific organisms have been identified as the cause, FUSOBACTERIUM NECROPHORUM is commonly isolated."

Thrush is the result of an anaerobic bacterial infection.

Things that can cause it:
The first thing is to assess the horses living environment, is it clean, does his/her feed get cleaned out on a regular basis. A hoof pick can go along way in curing and preventing thrush. As a general rule, when you have thrush and/or a recessive frog (and particularly when it's presenting in one or two hooves rather than in all four) and you can rule out environmental or maintenance factors, you have to start looking for other problems. And that usually means looking at some sort of compromised blood flow (vascularity) to the frog.

The next step, then, is to consult with your Farrier and vet to determine if they perceive any subtle causes for the condition or if they believe that the frog has simply atrophied from a previous condition that has been resolved. If you can rule out current problems and attribute the condition to problems that have been resolved, the next step would likely be to apply pressure (conservatively) to the frog and see if you can stimulate some vascularity. There are any number of ways this can be done, and your Farrier should make the call as to how s/he wishes to do it. What to do about it? I use wide web shoes, instruct my clients to clean the feet regularly, and treat the thrush with Thrush Buster. Bleach isn't going to cut it if it's chronic.

Primary cause is the environment; second to that Thrush very often gets established because of 'non-functioning' frogs which are a victim of contracted heels due to inactivity or subtle hoof imbalance from shoeing with no frog ground contact. I rarely see thrush in horses who live outdoors in large pastures , even when the feeding and loafing areas are 'pea soup' all winter. Thrush is often a lack of frog function, not wet environments. Along with medicating,(and I agree that Thrush Buster is the best I have seen) you and your Farrier need to re-evaluate the shape of the horses hooves and the footfall of the horse to see if there is a hoof function problem. If his feet are contacting the ground 'toe first' at the walk, it is an indication of improper hoof balance and/or subtle lameness.

A consistent 'toe first' landing prevents the entire rear portion of the hoof from functioning properly, contracts the heels and frog, and establishes a nice airtight place for the bacteria to get established. The heel landing and contracted heels are usually caused (inadvertently) by the Farrier's honest attempts to balance the foot using traditional methods. The frog should be on or near the ground, after the heels of the foot are trimmed correctly, so it can be stimulated by the ground support. If the frog is elevated above the ground by tall heels, it can not function.

The heels of the foot should not be under run (crushed forward). They should be trimmed back so they are short and the horn tubules straight, so the frog and bars can function to expand the entire rear of the foot (including and especially the heels bulbs) upon impact with the ground.

Check the shape of the bottom of the hoof. Draw a line across the widest part of the hoof (usually about 5/8" behind the tip of the frog). Then measure the length from your line forward to the point of break over. This point may be the front of the toe or the spot where the toe of the shoe is worn from wear, or is rolled or rockered by the Farrier).

Then measure from your line back to the heels. The rear section should be noticeably longer than the front. If the front section is longer than the rear, I guarantee you have a shoeing problem which is contributing to the limited function of the structures in the rear of the foot. Addressing hoof balance and function is the first step in curing thrush. It is probably heels which need to be trimmed more, and the break over of the shoe set back further.

Even if the heels are trimmed down enough, it is vital to remember that the length of the front of the hoof directly impacts the function of the rear. Both ends of the hoof need to be addressed at the same time. If you do not get the entire foot/frog working and the rear of the hoof expanding properly, the battle will be ongoing.

Basically, when you have a severe case of thrush (i.e., one in which sensitive tissue is involved), you have an open wound, and it should be treated as such. So don't go pouring anything on it that you wouldn't pour on an open wound on the horse's hip or face or whatever. Likewise, contact your veterinarian to ensure that your horse is adequately "boosted" against tetanus.

No matter how clean the environment you keep a horse in, the bottom line is that he's going to get dirt, mud, fecal matter, and urine, contacting the solar surfaces of the hoof capsule. Since the capsular surfaces are comprised of dead tissue and have no direct blood supply, they don't have any way of combating anaerobic bacteria and, in fact, provide a great breeding ground for anaerobic activity. Once this activity is established, you get pockets and crevices, which serve to trap more bacteria and you, find that even if you successfully treat the condition, it quickly reoccurs. To avoid such reoccurrences, you need to pack the voids and crevices (all of the inviting environments) with something productive so that the non-productive stuff (e.g., manure) stays out.

You can use any number of things for packing. I normally opt for Hawthorne's Medicated Sole Pack. It's guaranteed to kill thrush, but--more importantly--it will provide a barrier to keep it from recurring while the hoof regenerates and rebuilds its natural barriers.

Once thrush is established, it is important to debride the area and ensure that the diseased tissue is appropriately trimmed back and/or removed; otherwise, even in clean conditions, the condition will linger. Likewise, thrush will tend to "hang on" in an imbalanced or diseased hoof. I suspect that this is a result of compromised vascularity within the hoof. Subsequently, you'll want to ensure that the horse is being trimmed regularly and that the horse is getting sufficient exercise/activity to stimulate circulation.

Do's and Don'ts in treating Thrush:

There are many products on the market manufactured specifically formulated for treating thrush. For the most part stick to one of these products. The one that I believe works the best is 'Thrush Buster'.

If the thrush is really bad and the frog is split or eaten away after debrideing the area use Hydrogen Peroxide and a small brush to clean and disinfect the area and then apply Thrush Buster. In a pinch out of a product specifically formulated for treating thrush you can use regular household bleach. Never use Formaldehyde to treat thrush. It will harden the top layers of cellular tissue, leaving the underlying tissue soft. This is a bad situation as the hardened tissue will break up and crack and generally become de-structured. Formaldehyde is a good theoretical agent to use against the organisms causing thrush, but the reaction with the tissue of the frog makes it totally unsuitable and may well be contributing to the split.

Remember; when you have a severe case of thrush (i.e., one in which sensitive tissue is involved), you have an open wound, and it should be treated as such. So don't go pouring anything on it that you wouldn't pour on an open wound on the horse's hip or face or whatever. Likewise, contact your veterinarian to ensure that your horse is adequately "boosted" against tetanus.

Contributor: Bill Mayfield of Mayfield Farrier Service