Internal parasites are powerful predators. They are ever present, and they stalk the weak, the young and the infirm. Managing parasites is a must to keep your horse at his best.
The ?Big Four? in equine parasites are large strongyles (bloodworms), small strongyles (cyathostomes), tapeworms and roundworms or ascarids. In some areas bots, pinworms and other less common parasites can also be problems.
For the most part, they?re a problem of horses that get to graze. If your horse lives in a pristine stall and doesn't graze at all (not even at a show), his parasite load likely will be small.
Strongyles and roundworms are direct life-cycle parasites, meaning they don't need another animal as an intermediate host. They?re perfectly happy dealing with just horses. Eggs and/or larval stages end up outside via manure and develop on the lower layers of grass and upper soil.
Tapeworms use tiny mites as an intermediate host. These mites are present on grass outdoors. The mites eat tapeworm eggs from the segments passed in manure and then your horse consumes them.
Now, even if you think you know it all on parasite control, don't turn the page before you read this: Controlling worms by reducing exposure is becoming critical, as parasitic resistance to the drugs we currently have to fight them is on the rise. With no new medications on the immediate horizon, every effort we make toward better management will help the fight.
You?re not going to get your horse totally parasite-free, and in fact, that might not be good. Many horses develop natural immunity against parasites as they mature. Roundworms are a scourge in foals but rarely bother an adult horse. Some adult horses even show natural resistance to the strongyles and are ?low shedders,? passing few eggs in their manure.
But that doesn't mean you can ignore them either. it's just that from an economic standpoint, why pay to feed a bunch of worms as well as your horse'
Realistic Clean Up.
The ideal solution is to have your horse wear a manure catchall, like carriage horses in cities, so you can dispose of it without him ever touching it. You could also follow your horse around all day scooping manure before it hits the ground (once manure hits the ground, it breaks up enough to release eggs so even frequent pasture pickups won?t catch all the eggs). Certainly picking up manure in the pasture on a regular basis can't hurt, but none of these options is realistic.
Look at your fields and pastures with a critical eye. With enough room, horses practice parasite control themselves. You may notice patchy areas of tall grass and other areas eaten down fairly short. The tall areas are where the horses deposit their manure. They then avoid eating that grass, which is undoubtedly heavily parasite-contaminated.
Unfortunately, land is a luxury these days, and overcrowding forces horses to graze near those contaminated areas. Sadly, it's often the most susceptible-to-parasites horses that end up there?the young, older horses and horses with any infirmities.
Spreading Is A Drag.
Recommendations for environmental control usually include dragging your pasture frequently to break up manure and spreading it, so the eggs and developing larvae die. That does help IF it's done in hot weather, as exposed larvae are sensitive to heat. Horses then shouldn?t graze on the area for several weeks, to allow for a break in the cycle.
Unless your manure is composted (and checked for temperatures in your compost pile?they should reach 135 to 150° for several days or over 90° for at least two weeks), don't spread it. Make sure your composted manure is located away from pastures, so a heavy rainfall doesn't simply spread eggs and larvae back on the grazing areas.
Rotating pastures is a good option. With temporary fencing you can ?strip? graze areas, so weeks go by before your horses return to the same section. This requires time, additional fencing and manpower, which may be unrealistic for many of us. Depending on your horse, using temporary fencing may not be wise for him either.
Another way to rotate grazing areas is to swap your horses with some sheep or cattle. Most parasites are fairly species specific, so they won?t develop in the ?wrong? host. This naturally breaks up the life cycles of the parasites.
Keeping your horse stalled, on dirt paddocks or dry lots will cut down on parasites. Clean, dry stalls don't provide the moisture for development. On the other hand, very wet, dirty stalls kill developing parasites with the ammonia concentrations (no, you can't use this as an excuse for having dirty stalls).
Dry lots don't provide the moisture and plant life that makes an ideal environment for developing larvae. Using feeders to keep forage up off the ground and away from mite hosts or plant life and moisture important in the life cycles can help.
The weather can help you in your battle against many parasites. Developing larvae are often susceptible to high temperatures, so Southern horses are actually at more risk grazing in the winter than during a hot summer. Unfortunately, most larvae are resistant to cold temperatures and even freezing. While they may not develop, they don't die off either?they simply wait for better conditions.
When it comes to bots, fly sprays and fly sheets can keep these parasites down. It also helps to ?strip? the eggs off your horse daily with a bot knife. Some people have good luck with holding warm cloths over the areas with eggs attached, stimulating the eggs to hatch. Exposed to the air, these parasites will die.
If you're disappointed in this basic advice, we understand. But it's time to find non-drug methods for reducing parasite infestation. Resistance is real.
While the broad-spectrum super drugs (ivermectin and moxidectin) are still reliable (so they remain the simplest, most-reliable method), it's only a matter of time before ?super worms? learn to avoid them, too.
Next month, we'll tackle target deworming, using fecal egg counts, specific drugs for specific parasites, and how to determine what might work best for you and your horse.