b'The FEC result is a snapshot in time. dewormers, this population built up a re-Shedding will change based on season,sistance to the anthelminthic drug, leav-age, and the stress level of the horse,ing a small percentage of highly resistant says Damita Hansen, DVM, of Cornwal- ones who then reproduced, creating even lis Veterinarians Ltd., in Nova Scotia,more resistant populations, she explains. Canada. As a horse ages, many factorsChanging the thought process about and conditions may raise or lower itsequine parasites has been an uphill battle, normal shedding level. This is why it issay our sources. Instead of clearing a important to continue to monitor FECs athorse entirely of parasites, due to drug least yearly, even on horses who are previ- resistance the new goal is to focus on ously low shedders.those horses that are shedding the most. One step beyond an FEC is a fecal eggSmall burdens of strongyles typically are count reduction test (FECRT). To me, annot harmful in horses so, instead of treat-FECRT is as, or more, important as aning with a dewormer, veterinarians now FEC, says Hansen.recommend monitoring.An FECRT is the only way to defini- We have to try to identify the horses tively assess parasite resistance against awho are highly susceptible to parasites drug in a stable. This test involves obtain- and who are shedding the most eggs into ing a fecal sample and submitting it fortheir environment, says Olds-Sanchez. analysis, administering a dewormer, andWe target those horses more aggressively taking another fecal two weeks later.with properly dosed, properly timed, ef-An FEC is performed on both, and thefective dewormers. difference between the two samples isWhy should you, a horse owner, care calculated as a percent reduction, saysabout dewormer resistance? If we con-Hansen. A low percent reduced indicatestinue to see increased resistance to the that not many worms were killed by thenewer drug classes that used to be 100% dewormertherefore, the dewormereffective, we may end up with no effective was ineffective, or the worms showeddewormers for our horses, and parasite resistance. This is especially importantdisease and even death will potentially for moderate or high sheddersyou wantincrease, she says.to ensure your dewormer is effective and (the worms in) your individual horse (are)Parasite Typesnot developing a resistance problem.Small Strongyles The most common of the parasites well discuss here, your Anthelminthic Resistancehorse has likely carried some small Anthelminthic resistance is quicklystrongyles (cyathostomins) in his lifetime. ARND BRONKHORST/ARND.NLbecoming one of the biggest issues facingAdult horses, even with moderate loads, equine medicine. What were once suchmight show no signs of disease. Some-effective dewormers are now no longertimes they lose weight and experience treating a horses parasitic burden. Thediarrhea. Rarely, small strongyles can old school of thought for treating largecause a very serious problem in the horse strongyles (more about these worms oncalled larval c yathostominosis.page 26) was to use a different dewormerThis condition primarily affects horses to move forward with treatment.type every two to three monthsin otherunder age 4. They often show signs such It is a rough estimate of the parasitewords, to rotate dewormers. While it wasas sudden weight loss and overwhelming burden that your horse has inside ofeffective in eradicating large strongyles, itdiarrhea, as well as colic, dehydration, the gastrointestinal tract, says Allisonimpacted other parasite species.and ventral edema (fluid swelling under Williard, DVM, of Auburn Equine, inThe unexpected and unintendedthe abdomen). These horses can look like California.consequence of the frequent rotationaltheyre suffering from salmonellosis or Dont expect your horses FEC to bedeworming programs was the devel- Potomac horse fever, which the veterinar-0, however. Veterinarians classify horsesopment of multidrug resistance in anian should rule out. in one of three categories based on theiremerging small-strongyle population,The condition occurs after the stron-FEC results: low (under 200 epg), mediumsays Ashleigh Olds-Sanchez, DVM, Dipl.gyle larvae emerge from the intestinal (200-500 epg), and high shedders (aboveAVBP-Equine, of Galisteo Basin Veteri- walls, where they can remain dormant 500 epg). Guidelines suggest, regardless ofnary Services, in Santa Fe, New Mexico. for months or, in areas with well-defined the count, treating horses twice annuallyThis deworming protocol left a smallseasons, years. This means the horse to rid the system of tapeworms and anypopulation of this other strongyle spe- stockpiles strongyles during grazing other parasite not picked up on the FEC.cies alive. With constant exposure toseason, which can result in thousands of TheHorse.com|The HorseApril 202025'