Gasterophilus spp Average Cost

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What is Gasterophilus spp?

The bot fly looks similar to a bumblebee with a hairy head and can be yellow and brown, black and white or black and yellow. Your horse may not have any symptoms at all, but some bots can carry diseases or produce an infection that may create serious side effects. Also, the pain and irritation to the stomach may cause loss of appetite, which can affect nutrition and performance. The eggs are laid in areas where your horse can (and will) lick while grooming and this helps with the hatching stage and then transfers them to the mouth, where they will eventually make it into the stomach where they will hang out until the weather is warm again. The bot larvae are passed through your horse’s feces where they will bury themselves in the ground for about a month or two (depending on the weather) when they emerge and start the cycle over again.

Gasterophilus spp is a very common condition in horses caused by the bot fly (Oestridae). An average of 45% of horses become infected with gasterophilus spp every year, usually in the summer months to be hatched in the winter. There are three different types of gasterophilus spp, which are gasterophilus intestinalis, gasterophilus. nasalis, and gasterophilus haemorrhoidalis. These different types lay their eggs in different areas of the horse’s body. The gasterophilus intestinalis eggs are laid in the hair of the forelegs and shoulders, gasterophilus nasalis eggs are laid in the chin, nose, and eyes, and gasterophilus haemorrhoidalis eggs are laid around the lips. These bots (larvae) can create a mild to moderate gastritis and ulceration of the stomach, causing pain when eating.

Symptoms of Gasterophilus spp in Horses

Some things to watch for if you think your horse may have gasterophilus are:

  • Whitish-yellow eggs on front legs and shoulders (gasterophilus intestinalis)
  • Yellow eggs around neck and chin (gasterophilus nasalis)
  • Black eggs around the mouth and lips (gasterophilus haemorrhoidalis)
  • Agitation
  • Redness of the mouth and lips
  • Watery stool
  • Painful lesions in the mouth
  • Lack of appetite
  • Bacterial infection (watery stool, fever, and lack of appetite)


  • Gasterophilus intestinalis lay eggs on the limbs and shoulders
  • Gasterophilus. nasalis lay eggs on chin and neck
  • Gasterophilus haemorrhoidalis lay eggs on lips and mouth

Causes of Gasterophilus spp in Horses

The cause of gasterophilus intestinalis, gasterophilus. nasalis, and gasterophilus haemorrhoidalis are the same for all three, which is the bot fly. The only way to prevent this is to treat your horse for the infection every year if you are in an area where bot flies are known to be prevalent.

Diagnosis of Gasterophilus spp in Horses

If the eggs are still on your horse’s skin it should be easy to diagnose just by looking at the color and location of the eggs or bringing your veterinarian a sample to examine. However, it is recommended that you see a veterinarian that specializes in equine care to check your horse for infection or infiltration of the intestines and stomach. Your veterinarian will ask you about your horse’s history, including vaccination records and signs of abnormal activity. The veterinarian may be able to get a definitive diagnosis by identification of larvae in your horse’s feces if they are found. Otherwise, a complete checkup will be needed to rule out other conditions. Afterward, a thorough physical examination will need to be performed, which includes weight, height, body condition score, temperature, behavior, breath sounds, heart rate, and blood pressure. If your horse has any eggs, the veterinarian should be able to spot them right away. Next, the veterinarian will check for lameness by looking at the way your pet moves while they walk and trot. Then a hoof test, conformation check, and and flexion examination will be done. The veterinarian will briefly put pressure on the joints and inject a numbing agent before watching your horse walk and trot again.

In addition, diagnostic tests will be performed which will usually include a fecal examination, urinalysis, complete blood count, bacterial and fungal culture, blood chemistry panel, packed cell volume (PCV), and glucose level. Abdominal x-rays and ultrasound will be used to check for any damage or blockages in the intestines or stomach.

Treatment of Gasterophilus spp in Horses

The treatment for gasterophilus includes several stages, which are removing the eggs, treating the internal bots, and removing the bots from your horse’s living environment.

Removing the Eggs

Removal of the eggs is a long and tedious job, but necessary to control the infestation. There are a couple of ways to do this, which include using a sharp edged tool to scrape them off or using insecticide from the veterinarian.

Treating the Bots

Killing the internal bots is done by giving your horse avermectins or moxidectin at the end of the summer and then given annually in the early summer months to prevent future infestations.

Removing the Bots

The larvae are excreted in the fecal matter, so it is important to clean up the feces on a regular basis.

Recovery of Gasterophilus spp in Horses

Continue to watch for signs of bot fly eggs on the skin and larvae in the feces to prevent reinfection. Be sure to follow up with your veterinarian and call if you have any questions or concerns.