The Horse

APR 2019

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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TheHorse.com | The Horse April 2019 29 development of anthelmintic resistance. "Every time you use a dewormer you're pushing the worm population toward re- sistance," Jacobson says. "It's important to use dewormers carefully and not just de- worm on a calendar schedule. Sustainable control relies on understanding the im- portant parasites in your region, targeting treatments to horses that need treating, and using treatments that are currently effective against the target worms." She underscores the importance of maintaining refugia, the population of worms that doesn't get exposed to de- wormers because they are on pasture as eggs or larvae or in untreated horses. "Susceptible worms in refugia can effectively 'dilute' drug-resistant worms in the population," she says. "Interbreed- ing of the susceptible worms with any resistant worms slows the accumula- tion (of) resistance to treatments in the worm population. Restricting deworming treatments to horses with high FEC and leaving horses with low FEC untreated is an important tool to manage refugia for sustainable parasite control programs." Worm control must strike a balance between reducing the risk of disease in horses and managing the emergence of resistance in worms. "Because we value them as individu- als, the loss of a single horse is too great a loss," says Jacobson. "That means we err on the side of caution and develop control programs that aim to prevent disease, but do so with a long-term view of maintaining the effectiveness of the treatments we have." Nonchemical Parasite Management Managing the worm burden on pas- tures remains an important aspect of parasite control. You can accomplish this by removing manure regularly from en- closures and treating horses with high egg counts appropriately. Where horses are kept in small areas, pick up and compost manure (or remove it from the horse's environment altogether). "Nonmedical means for worm control are important," Nielsen says. "Cross- grazing with ruminant animals is po- tentially very effective. Chain harrowing or mowing can be useful, but timing is crucial and is dependent on where you are and the climate you have. Mowing in warm, wet conditions just spreads the worms around, meaning all the pasture is then contaminated. But in very hot weather, spreading manure around can be an effective control strategy, because the larvae will die off much quicker." Recently, a commercial biological product has become available in Aus- tralia that might serve as a nonchemical parasite control tool. It's composed of fungal (Duddingtonia flagrans) spores that feed on parasite larvae in manure after being fed to livestock (TheHorse. com/165635). "We don't know how the product is going to work out yet and how it could be implemented into a strategy as an adjunct to anthelmintic therapy," says Nielsen, "but the principle is well-researched." The Bottom Line Managing parasites and preventing worm-related disease in horses is a com- plex topic, with many things to consider. The AAEP recommends all adult horses receive "one or two yearly treatments to target large strongyles, tapeworms, bots, and spirurid nematodes responsible for causing summer sores (Habronema spp and Draschia spp)." Beyond this basic treatment, own- ers and veterinarians should use egg counts to guide their parasite control decisions, keeping in mind the following considerations: ■ How are the horses housed? (Alone? In herds? At pasture? In stables?) ■ What are they used for? (Do they travel? Are they stressed?) ■ What ages are the horses? (Foals? Youngsters? Old horses?) ■ What is the local climate? (Hot? Cold? Wet? Dry?) These factors can affect egg count levels, worm burdens, when parasites will be most active, and how and when they should be targeted. (See TheHorse. com/157317 and TheHorse.com/148466 for specific recommendations.) Deworming horses is not a simple mat- ter of dropping into the shop and buying a product, going home, and administering it. Work with your veterinarian to develop an appropriate strategy, beginning with fecal egg counts. Then, determine what anthelmintics are still effective on your farm. "That comes before anything else," says Nielsen. "And there is no way of tell- ing without (FEC) testing." h For the treatment and control of all major parasites including tapeworms. For use in horses 4 weeks of age and older, including stallions and breeding, lactating mares, up to 1,320 lbs. Anthelmintic and Boticide FOR ORAL USE IN HORSES ONLY (ivermectin 1.87% praziquantel 14.03%) Oral Paste EZE dose ™ syringe

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