Page 12 - 22 June 2012

DEWORMING
Parasite resistance has changed recommendations.
We need to be deworming to decrease pasture egg burden and decrease the exposure to eggs.
by Loni Taylor, DVM
There is an emerging problem of equine parasite anthelmintic resistance. The old-fashioned recommendation of deworming every two months with a different dewormer has not been effec- tive at preventing this resistance, so as a profession
we equine veterinarians have realized we have to do something differently.
Horses have evolved to have a mostly symbiotic relationship with worms and it is only when we have an overabundance of worms that we have disease. Knowing this, we have realized that we don’t need to deworm with the goal of keeping a horse parasite free; rather we need to be deworming to decrease pasture egg burden and decrease the exposure to eggs, ulti- mately preventing a high worm load in our horses.
Based on this philosophy, we now recommend performing a fecal egg count with no dewormer present in the system on adult horses (2-year-olds
and older) to find out a horse’s baseline egg shed- ding. There are some horses whose immune systems are better at eliminating worms than others, so some horses will be in need of dewormers more than others.
Egg shedding is quantified by the number of eggs per gram of feces. The main worm egg that we are concerned with in adult horses is the strongyle egg, and all these numbers will be based on strongyle counts. A low shedder has less than 200 egg/gm feces. Twice a year deworming is recommended for the low shedding horse. Because this is a strongyle count and based on current dewormer efficacy in
the area, I would recommend deworming this horse with Quest Plus in the spring and either Quest or an ivermectin product in the fall. (Your veterinarian can give you specific product recommendations based on dewormer efficacy in your geographical area.)
The next case would be that of a moderate shed- der, which falls in the 200-600 egg/gm range. These horses should be dewormed three times a year. The last block of horses are considered high shedders. These horses have egg counts of greater than 600 egg/gm of feces, and the major pasture contamina- tors. High shedders need to be dewormed every two to three months, depending on the products used. Again, check with your veterinarian for specific prod- uct recommendations.
There is a uniform resistance to both Strongid and low-dose Panacur with strongyles so I usually don’t rec- ommend using either of these dewormers unless a fecal egg reduction test has been performed on your herd and
you know these dewormers are effective in your herd. High dose Panacur (i.e. the Panacur Power Pack) is very effective, but with resistance to it at low doses I try to reserve it for use in horses that are truly showing signs of parasitism and not just for our routine deworming.
Foal and yearling care is very different as they are susceptible to different kind of worms and their immune system has not developed the ability to deal with worms near as effectively. I usually recommend using Anthelcide (oxibendazole) at the higher dose (15mg/kg) or switching between this and Panacur every two months starting at 2 months of age, as ascarids (the primary parasite of the young horse) is showing resistance to ivermectin and Quest is not approved for use in horses that young.
After 1 year of age I usually do a fecal egg count, but recommend using Quest instead of ivermectin based on the number of eggs/gm of feces.
The American Association of Equine Practitioners offers these additional tips to prevent parasites:

pasture at least twice weekly.

manure piles and expose parasite eggs and larvae to
the elements.

sheep or cattle, to graze them, thereby interrupting
the life cycles of parasites.

to prevent overgrazing and reduce the fecal con-
tamination per acre.

on the ground.

horse’s haircoat to prevent ingestion.
DR. LONI TAYLOR
Oklahoma City Equine Clinic 400 N.E. 70th St. Oklahoma City, OK 73105 (405) 843-1099
Worms are not always this easy to see. Fecal egg counts can find the hidden danger.
12 SPEEDHORSE, June 22, 2012
VETERINARY VIEWS
Stacy Pigott, Speedhorse