Bots & Beyond

All horses are at risk from these summer loving parasites. Whatever your climate, wherever your horse resides – stalls, pastures, dry lots – these parasites thrive during summer months. See how they can infect your horse, the damage they do, and how to stop them.

Bots (Gasterophilus): Female bot flies lay eggs on the horse’s hair. The eggs develop into larvae within five days of being deposited by the female . Larvae are stimulated to emerge by the horse licking or biting these developed eggs. The larvae either crawl to the mouth or are ingested. Once inside the horse’s mouth they bury themselves in the tongue, gums, or lining of the mouth. During this stage, the horse may experience severe irritation, as well as the development of pus pockets and loosened teeth. Loss of appetite may also develop. After approximately 28 days in the mouth, the larvae molt to the second stage and move into the stomach. The second and later third stage larvae typically attach to the lining of the stomach and the intestinal tract. They cause irritation and may block the opening to the small intestine as well as interfere with digestion; chronic gastritis, ulcers, colic and other conditions can result. Go to for more in depth information on bots.

Dewormers for Bots: ivermectin; moxidectin has limited control

Stomach worms (Habronema and Draschia): Responsible for producing “summer sores” or non-healing wounds and internal problems. Infection occurs when flies deposit infected larvae on the horse’s lips, nostrils, or open sores. When deposited in wounds, “summer sores” can occur. In large numbers, habronema can produce severe gastritis, and tumor-like enlargements may develop in the wall of the

stomach. If they rupture, peritonitis usually ensues.

Dewormers for Stomach worms: ivermectin; moxidectin controls only adult stage of Habronema

Equine Threadworm (Onchocerca): When a gnat carrying onchocerca larvae bites a horse, the larvae migrate through the bloodstream where they mature and release microfilaria. The microfilariae then migrate to the skin. Symptoms include small lumps on the chest, withers, neck, face, and belly; itching and rubbing, resulting in loss of hair and scaly skin; development of scabby, weeping sores; moon blindness and fistulous withers. The life cycle continues, as biting insects pick up the microfilariae from abraded lumps carrying infestation to other horses.

Dewormers for Threadworms: ivermectin

Don’t let these parasites interfere with your horse’s health this summer. Good News – Durvet’s Ivermectin Paste is very effective against each of these parasites. Important note: although fecal egg tests are a valuable tool in parasite control planning, they may not always indicate the presence of all parasite infestations. Talk to your local veterinarian for detailed deworming recommendations.

FACT: Durvet’s Ivermectin Paste targets 34 parasite species and stages, including all 3 stages of the 2 most common bots.

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