EQUINE THRUSH – WHAT IT IS AND HOW TO DEAL WITH IT

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Written By Walt Friedrich

It is a condition – or more precisely, an infection – in the hoof. It is not a disease. Its elimination has been the goal of massive efforts to develop the ultimate product, as witness the vast variety of thrush-busting products on tack shop shelves. All of them do sell, and each of them probably does reduce and control the infection in some hooves – but there are a couple problems: one is that a given product may clear things up for some horses, but seems ineffective for others. And secondly, many of those hooves whose thrush does get controlled end up with a re-infection a couple months later.  Right up front, the problem is not a simple one.

Just what is this elusive infection, anyway?

Well, that’s part of the problem. The term “thrush” gets hung on just about every hoof ache or pain that comes along, but it is not necessarily just one type of microbe that’s responsible. There are enough bad guys to fill a Post Office bulletin board, including yeasts, bacteria, and fungi! The most common of the “usual suspects” is a yeast named Candida albicans, a nasty little creature, and very difficult to eliminate. In addition to albicans, there are a number of other species within the genus Candida that are known to cause human and equine infections. And to add some complication, a bacterium called fusobacterium necrophorum is also commonly held responsible for many “thrush” infections, PLUS numerous fungi in the line-up as well. The invading army that causes “thrush” can have many mercenaries, and it is asking a great deal of any one treatment to go out there and kill ‘em all.

As if that’s not complex enough, yeasts and fungi exist in both “live” and spore form. Consider the spore to be an “egg”, containing the microbe, which “hatches” when environmental conditions are favorable. Killing an army of microscopic fungi may be doable, but the spores they leave behind are virtually bullet-proof; they patiently wait for those favorable conditions to return, at which time they “hatch” and re-form a brand-new army!

Tackling the problem…then back to the drawing board

So here are we, one day, observing our horse three-legged lame, perhaps, with a gooey, stinky mess exuding from a frog. “Aha,” we think, “this is thrush and I’m gonna get rid of it.” Of course, we don’t know what organism or organisms are responsible, so we ask the guy in the tack shop for the best of the thrush killers, we buy it, then take it home and have at it. Sure enough, after a few applications, things appear to getting better, the frog is healing, the goo and the smell are gone, and our horse is happy – until a few weeks later, when we see a rerun of the problem developing. The spores have hatched and have started to party again, plus some new neighbors from the stall floor have joined them, and we’re ready to return to the tack shop to look for a newer and better anti-thrush miracle cure.

More about these nasty little critters

One of the basics we know is that we can be dealing with two entirely different entities, here – aerobes and anaerobes. Aerobes live and breathe even as do you and I, which means they need air to survive, which makes them relatively accessible to our attacks. That opens the field to most of the on-the-shelf products that we wipe on or spray on. These are the easiest to apply, and when they work, our job is easier.

The anaerobes are quite another story. They cannot live in air, consequently, when without a host, they exist in spore form, sort-of in a state of suspended animation. But those spores, along with their aerobic cousins, cover the stall floor and walls, even the very dirt we walk on, even our own shoes! It takes two things for an infection to hit a hoof: the hoof needs to be standing amid the microbes (that’s a “gimme” – if he’s in the stall, he’s standing amid them, and standing anywhere in mud or feces, it’s like he’s put out the welcome mat for infection), and the hoof needs to have some “outside doors” open – any tiny lesion on the bottom of a foot will do. Both microbes and spores get jammed into the lesion, where they get sealed in when the horse stands or walks in mud. The living microbes are already at work, and when the spores realize that there’s no air, it’s warm, it’s moist, they burst forth and join the party.

How to fight back

Now we start to see the complexity of fighting “thrush”. Topical treatments work on aerobes because we can get at them. But not so for the anaerobes. Living in an airless environment means they are buried deep in the tissues, hard for us to reach. A new approach is called for; soaking those feet in the appropriate microbe-killer long enough for the medication to soak in and do its job. A 30-minute soak in apple cider vinegar or dilute chlorine dioxide (Oxine or White Lightning, for example) will do the job on the microbes, but not their spores. For that, soaking in a product designed to kill spores is needed. There are several on the market, but the most effective may be CleanTrax, available on-line – it will kill aerobes, anaerobes, and spores.

So when you can see deterioration of the frog, and/or smell a real stink on those hooves, the “enemy” is obviously present and you can deal with it. But the real trick in dealing with it is to catch it early, before much damage has been done, and for that, some preventive measures are called for. When thoroughly cleaned, the entire bottom of the hoof is in clear view – difficult for undesirable microbes to hide. Consider forming the habit of thorough picking and wire-brushing the hoof bottom clean, a quick scrub with Dawn Detergent, every day, then spraying the entire surface with a microbe-killer; keep the foot off-ground for fifteen or twenty seconds to allow some penetration of the spray. Two very useful sprays are colloidal silver (silver ions are believed to destroy key enzyme systems in the cell membranes of these pathogens), and Usnea (a symbiosis [one organism living on another] of a fungus and an alga, used for its antibiotic and antifungal properties). Both are available on-line: consider the colloidal silver brand, “Silvetrasol”, about $20 for a spray bottle, and Usnea Tincture, about $10 for four oz., available from Essential Wholesale & Labs, among others. Mix Usnea 50-50 with water and spray daily, but Silvestrasol once a week.

Preventive medicine

Spraying is a quick and easy preventive procedure – but take it a step further and disinfect any crevices you see. For example, a healthy hoof has no crevices or clefts (the commissures don’t count), but a potential problem will show up as a cleft developing in the center of the heel of the frog. It will usually be just a slit, but if you can insert the metal tip of your hoof pick into it to any depth at all, it’s a problem in development. Left untreated, that cleft will develop into a crevice that’s as deep as your pick’s tip is long – or deeper. That means trouble is coming, and you should take countermeasures right away. Such clefts are well-protected hidey-holes for thrush-causing microbes to start their damaging work. The trick is to deposit some microbe-killer directly into the bottom of that cleft, and to do that you need a special, inexpensive, syringe (no needle). Your vet can probably provide you with one; it has a long, flexible tip that allows you to get it into tight quarters. An alternative is to buy the product, “ToMorrow”, from your local Agway, Tractor Supply, or equivalent. ToMorrow contains medication useful in treating mastitis in cow udders, hence its long, flexible tip. You can use it to deposit a pea-sized glob of medication at the very bottom of a frog cleft. You can use the mastitis treatment cream itself in frog clefts, but a better alternative is to empty the syringe, and then refill it with a 50-50 mixture of Triple Antibiotic Cream and Clotrimazole, both available on your druggist’s shelves. TA Cream is effective in combating Athlete’s Foot – a fungus infection – and Clotrimazole is a powerful treatment, especially useful in combating thrush. Added bonus is the cost for one ToMorrow syringe is only about two bucks.

The outlook is positive

And so, with all this, we’ve not yet crossed home plate – but we’re on third, waiting for the base hit that lets us score. We have a pretty good idea what causes the thrush condition. We have not yet found the silver bullet – but we’re getting closer. The thrush condition in horses is actually quite similar to the human version, and when we are able to nail it completely in humans, we should have it licked in horses, too. Meantime, we do have means to control it and make our equine partners more comfortable while we’re at it. It’s so insidious that it can slide in under the radar and our problem becomes repair rather than prevention; but to prevent takes vigilance and some effort on our part. So for our horses’ sake, keep the stalls clean, keep the floors cleared of feces, keep them clear of mud, keep that pick and wire brush close at hand and use them daily. Catch it early!

Equine Parasite Management

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Written By Dr. Kris Hiney

Last month we introduced you to the major internal parasites which can plague your horse. This month we will discuss management strategies that you can use to decrease the parasite load on your horse, in part through an understanding of their life cycle. We can actually use the horse’s environment to help decrease our reliance on de-wormers and do our part to aid in the battle of anthelmintic resistance.
If you remember the life cycle of our most insidious parasite, the small strongyles, you know that the tiny infective larvae hatch from eggs outside of the horse. They then use the dew or moisture present on the grass to be able to wriggle around in the blades of grass and await your horse to come along and ingest them. Since they need this moisture as part of their life cycle and to be mobile, horses housed in stalls and dry lots are far less likely to be able to pick up infective larvae. It is pasture grazing, therefore, which is the key to the strongyles’ survival. Worm larvae will tend to be located in the thicker grass areas of the pasture and down in the thatch layer, where moisture remains longer.  The highest potential for infection will occur if your horse crops the grass close to the ground.
If you observe horses natural feeding patterns, horses tend to graze pastures into areas of roughs and lawns. The lawns, characterized by short grasses,  are the areas which are cropped closely to the ground and the roughs, which have longer grass, are the areas where horses choose to defecate and avoid grazing. Obviously the larger the area in which horses are kept, the less likely they are to graze near infective piles of horse manure. This will decrease their chances of picking up larvae. As stocking density of the pasture increases, or vegetative growth decreases, such as in times of draught, the horses will be forced to eat nearer these thick areas of grass just teeming with swarms of larvae. If the grass becomes too short, supplemental hay should be provided to avoid forcing the horse to graze in the roughs. Additionally, the pasture can be mowed to keep the roughs from spreading further into the pasture.
Many people employ dragging the pasture to break up manure piles and spread them through the pasture to prevent the formation of roughs. However, if you use this strategy, you must understand that you are effectively dispersing the eggs and larvae far more thoroughly than they could ever do themselves. Even on their own, larvae can spread 4 to 12 inches from their original pile, and even further if aided by heavy rainfall. Therefore, if you drag the pasture, keep the horses off the pasture for at least two weeks. Preferably the dragging should be done in the hottest part of the year in order to expose the larvae to heat and dehydration. Cool temperatures allow the larvae to survive longer, so it is not advised to drag during the spring and fall.  If you must drag in cooler weather prevent the horses from grazing for an even longer period of time. As strongyles larvae are especially hardy and can survive winter quite easily, this is really not a good strategy for trying to kill the larvae.  Finally, if you are going to spread manure on pastures as a means of disposal, never spread fresh manure. Make sure it has been thoroughly composted before applying it to your pasture.
In an ideal world, pasture rotation allows the best management strategy to reduce strongyles infestation  in your horses. Horses grazing in fresh new pasture will avoid grazing near manure piles, and have a lower chance of re-infesting themselves. Letting pastures lie dormant will also allow any eggs or larvae present to die before horses are introduced. If space and equipment allows, putting pastures into hay production will allow parasites to die as well. Finally, if you own multiple species of animals, grazing pastures alternatively between cattle, goats and sheep will reduce your parasite burden, as the worms are host specific. Obviously all of these strategies do require a significant amount of acreage and fencing to be effective and may not work for everyone.
Remember, for strongyles elimination, heat is your friend. Only drag pastures during the hottest part of the year, and do not allow horses back onto the pasture for at least two weeks. Use separate pastures for winter pasture and summer pasture. Remember, winter does not kill the parasites. In cooler climates, parasites will not die after emerging from their dormant state until about June, May in hotter climates. If you do have a clean pasture, before you turn horses onto it, chemical deworming can prevent parasite infestation. Horses that are dewormed should be held on dry lots for several days before turning them out. This will allow all the eggs that the mature female has deposited to pass through your horse’s digestive tract. When your horses enter their new pasture, they won’t be bringing any “friends” with them!
What about the other parasites in your horses life other than strongyles? There are certainly management strategies which will help control their populations as well. For ascarid control, remember that these worms are primarily a problem for young horses. If possible and space allows, rotate which pastures house young horses with adult horses. However, even this may not be completely effective as ascarids can remain alive in the environment for several years. Essentially, if foals and young horses have been housed in a pasture, it is fairly likely that ascarids are present. Unfortunately, as ascarids don’t involve the same strategy for survival as strongyles, they can also infest the young horse in stalls and dry lots. This is typically why young horses are dewormed more frequently than older horses.
Stomach bot larvae and adult fly control are unfortunately only going to be controlled through the use of anthelmentics. The adult form can fly for miles so even if you have a great deworming program, if your neighbors do not, their flies will simply fly over to your property to lay eggs on your horse.
Tapeworms are relative newcomers when discussing parasites in horses. While not new to the horse, they are new to us, so not as much is known about them. They are believed to have a similar susceptibility to climate as the small strongyles, but may be hardier. More horses in northern climates have been exposed to tapeworms, which would indicate that these parasites are relatively cold resistant, but may have a susceptibility to heat. Therefore, follow similar management protocols as you do for small strongyles control.
From looking at the parasites life cycle and their means of infesting horses, it is clear that horses are often dewormed more frequently than is really necessary. As anthelmintic resistance becomes a growing issue in horses, we need to understand the ways in which we can manage horses to reduce their parasite burden. Next month we will tackle the issue of anthelmintic resistance and discuss which deworming strategies might be the most correct option for your horse.