Vet's Corner: Equine Parasites: A Constant Threat
By Hoyt Cheramie, DVM, MS
Manager, Veterinary Professional Services, Merial
With approximately 40 parasite species waiting
to infect horses, controlling parasites throughout
the seasons can set horses up for a healthy year.
"All species and stages of parasites that a horse
may face cannot be treated during one single
time of year," says Hoyt Cheramie, DVM, MS,
manager, Equine Veterinary Professional Services,
Merial. "Even through the winter, we can still see
active parasite infections."
Although bot flies are generally seen during
the summer, horses are often assumed to be
infected with the gastric stage of bots, the most
damaging stage, during the winter months.
Large numbers of bot larvae can interfere with
digestion and even cause death in the event of a
stomach rupture.
In addition to bots, roundworms, or ascarids,
also may be a concern heading into spring. Foals
can shed ascarid eggs in the winter, potentially
exposing other horses in the barn. In severe
roundworm infections, foals can appear to be
in poor body condition, lack energy and can
occasionally colic.
Even under the best management practices,
horses are likely to be infected with parasites.
Management tips to control parasite populations
include preventing fecal contamination in
feed and water troughs. However, a regular
deworming program can help 
ensure the
parasite life cycle is interrupted.
"A broad-spectrum dewormer will help control
the many species and stages of parasites year-round,"
Dr. Cheramie says. "It's also important
to consult your veterinarian for a deworming
program that meets your specific needs."
Choosing a dewormer like ZIMECTERIN® Gold
(ivermectin/praziquantel) will help control 47
species and stages of parasites, including the oral
and gastric stages of bots. Plus, it's approved for
use in foals as young as 2 months old.
"With parasites, there is no time to let your
guard down," Dr. Cheramie says. "Regular,
ongoing parasite control can help keep horses
healthy year-round."