Summer Parasite Concerns

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You dewormed your horse this spring, so he’s good until fall, right? Not necessarily. Depending on his risk factors for parasite infection, your horse could need additional deworming treatment. Risk factors can include:

  • A fecal egg count (FEC) test result of more than 200 eggs per gram (medium shedder or higher)
  • Feeding on the ground without a bucket
  • Being housed in a stall or dry lot
  • Moderate or high pasture population (one or more horses per acre)
  • Limited manure removal
  • Rotating or sharing pastures with cattle, sheep or goats
  • Movement of horses on and off the farm to shows, for example
  • Age of horse

Parasite concerns can vary during the summer and include pinworms, neck threadworms and ascarids, also known as roundworms. All three parasites can be acquired in stabled horses as well as those on pasture.

Outward signs of pinworm infection often include an irritated tailhead. As a result of the itching sensation, horses rub. By rubbing, horses can spread pinworm eggs throughout their environment to stalls, fence posts and more. This can quickly spread the parasite eggs to other horses. Pinworm eggs are hardy and can persist in the environment for relatively long periods of time.

Neck threadworms (Onchocerca cervicalis)infect adult horses often causing itching and subsequently rubbing which can result in loss of hair, scaly skin, sores and small bumps on neck, chest, withers, face and belly. The adult worm lives around the ligament which runs along the top of the horse’s neck, so often times the horse will rub this area causing its mane to thin.

“Ascarids are resistant to environmental influences and are the key parasite of concern in young horses, under 2 years of age,” said Dr. Kenton Morgan, senior veterinarian, Equine Technical Services, Zoetis. “In foals, ascarids can cause poor growth, airway inflammation and small intestine impactions.”

However, it’s important to keep in mind that the majority of horses infected with parasites do not show outward signs, noted Morgan.

“The most important tool in your parasite arsenal is your veterinarian,” said Morgan.“Prior to deworming, ask your veterinarian to conduct a fecal egg count test to establish a baseline.”

Your veterinarian also can test your horse or herd to see if the dewormer you used was effective. A fecal egg count reduction test (FECRT) will show if the deworming treatment worked or if your horse has parasites that have become resistant to a specific active ingredient. This test is done after your horse or herd has been treated. Your veterinarian can then help you select additional treatment options if needed.

Visit IDMyHorse.com or download the EQStable app to answer a few questions about your horse and input his FEC shedding level to help develop an Individualized Deworming treatment plan.