Moderate Risk
- Same as Plan B, above, but add another fecal egg count check eight weeks after your November deworming if the dewormer was an ivermectin/praziquantel or 12 weeks after if a moxidectin/praziquantel dewormer was used. This is to check for emergence and maturation of any very early stage small strongyles, which neither moxidectin nor ivermectin will kill.
High Risk
- Check fecals, or deworm, at intervals appropriate for the last deworming drug used, i.e., six to eight weeks after ivermectin, 10 to 12 weeks after moxidectin, four weeks for all other drugs. If using a daily dewormer, check fecals at least twice a year.
- Deworm twice a year, at the beginning and end of grazing season, using a praziquantel and ivermectin or a moxidectin product.
- If rotating using drugs that can induce resistance, check fecals twice a year, four weeks after the horse has been dewormed with that product, right before your next scheduled deworming.
- Sample A: November - deworm with ivermectin/praziquantel. January - fecal or deworm with ivermectin. March - fecal or deworm with ivermectin. May - deworm with praziquantel/ivermectin. July - fecal or deworm with ivermectin. September - fecal or deworm with ivermectin. Note: If you substitute a non-ivermectin product (other than moxidectin) for any of these dewormings, you will have to do a fecal check, or deworm, in four weeks instead of eight.
- Sample B: November - deworm with moxidectin/praziquantel. February - fecal or deworm with moxidectin. May - deworm with moxidectin/praziquantel. August - fecal or deworm with moxidectin. Note: If you substitute ivermectin for any of the moxidectin dewormings, you will need to do fecal or deworm in eight weeks instead of 12. If you substitute a non-ivermectin product, you will need to do a fecal or repeat in four weeks instead of 12.
Any horse showing clinical signs that could indicate parasitism, such as poor coat, poor hooves, slow growth, trouble holding weight, a pot-bellied appearance, colic or change in manure, should be checked by fecal egg counts.
To Drag or Not to Drag
Dragging pastures - the practice of pulling a chain or harrow through the field to break up manure piles - definitely has pros and cons.
Early developmental stages of strongyles are very sensitive to drying, so disrupting piles of feces can result in their death. However, the stage that is actually capable of infecting a horse (called L3) has a protective coating and won't be bothered by low moisture. This means that dragging can actually spread these infective larvae around. Whether killing off younger forms before they can mature to infective larvae outweighs the risk of spreading infective ones is debatable. However, since horses instinctively will not graze around manure anyway, it may be wiser to just leave nature as is.
If dragging pastures to spread manure as fertilizer is part of your pasture management plan, simply take some precautions. The best time to drag pastures is when temperatures are high. Under those conditions, larvae mature to the infective stage rapidly, quickly use up their stored energy supplies, and die. Do your dragging in late summer, and remove horses from dragged pastures for 10 days to two weeks if you live below the Mason-Dixon line; four weeks for states north of this line.
Also, you need to take special care with foals because of their high susceptibility to parasites. Begin by deworming the mare a month before foaling to minimize the parasites she is carrying. Move her to her foaling stall only after that deworming. Within 24 hours of foaling, deworm her with ivermectin to prevent strongyloides larvae in the milk.
Whenever possible, turn mares and foals out in separate fields/paddocks that have not been used for high-risk horses for at least a year. Start foals on a regular deworming schedule between 1 and 2 months of age. If using drugs known to have resistance problems, check fecals regularly.
Another important part of your deworming strategy it to forgo turning out new horses with your present herd until you know the new horses' parasite status. Have a fecal egg count done on any new horse if he was not dewormed recently, or if he was dewormed with anything except ivermectin or moxidectin. (No resistant strains have emerged to these two drugs yet.) If the horse has parasites, deworm him with whatever drug you are currently using. Be sure to repeat the fecal egg count after deworming to make sure the parasites he is carrying aren't resistant. Your vet will advise you how long to wait after deworming to recheck, which depends on the product you are using.
If the horse had recently been dewormed with ivermectin or moxidectin, find out the date of the treatment and do a fecal egg count six weeks after treatment with ivermectin, or 10 to 12 weeks after moxidectin. If the egg count is positive, follow the procedure above - deworming the horse with the drug you are currently using, but being sure to recheck the fecal if you use anything except ivermectin or moxidectin.
With parasites, it's the right strategy for your situation that will best serve you and your horse.
