Parasitic Worms in Horses are becoming Resistant
Dr. Byrd and Dr. Cheramie offer some hands-on, useful tips for horse owners to put into immediate practice:
Did you know that in early morning hours worm larvae will crawl to the top of a blade of grass, then descend to the roots once the temperature heats up? Or that a single dewdrop can harbor over 100 strongyle larvae? To manage a horse’s environment to minimize parasite exposure, it’s important to understand a parasite’s lifecycle and habits, and take them into account as you design your environment management strategies:
- Remove manure from a pasture at least twice weekly, before larvae become infective.
- Dragging a pasture is OK, but do it during the hottest part of the day when exposed worm eggs and larvae are more likely to die off, not in the cooler morning and evening.
- Keep grass mowed short; it provides fewer places for worms to hide.
- Dry lots and stalls are less likely to be a problem, provided manure is removed regularly and the area is kept clean.
- Areas where foals and weanlings are kept can be hosed down to remove eggs; hosing is unlikely to kill the eggs.
- When possible, an open grassy area is a better foaling option for mares than a dirt-packed stall floor with bedding on top. If a stall is necessary, power-wash the walls, floor, and mats in between horses to minimize ascarid egg populations.
Counting parasite eggs in manure is something we’d gotten away from as over-the-counter dewormers became widely used. Now, as we need to be more selective and targeted in our anthelmintic use, it makes sense to know what, where, and in whom the target is.
- Have your veterinarian perform fecal egg counts for your horses before they’re dewormed, and keep track of the numbers over time to get a good picture of what’s happening. Use an Internet service like Horsemen’s Laboratory if you want to collect your own samples and mail them in for evaluation. SmartPak also makes a self-collection kit, which can be used to collect fecal samples from other types of animals as well as horses.
- Deworm high-shedding horses more often, low-shedding horses less frequently. Fort Dodge Animal Health has developed a helpful ‘Worm Smart’ PDF with a chart showing shedding classifications, plus a suggested deworming schedule for each shedding class.
- Use a dewormer that’s suited to your parasite population. Consult your veterinarian to determine if a rotational cycle of medications is needed or warranted.
- Isolate new horses. Perform fecal egg counts and deworm appropriately before introducing them to your established herd.
Lisa Kemp is an award-winning writer and marketing consultant for the equine industry. Her definition of a good day is one filled with any combination of horse people, horse images, horse stories, and yes, actual horses. For additional information, visit www.KempEquine.com