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Bot Flies in Horses - Symptoms & Prevention

Bot Flies in Horses - Symptoms & Prevention

When your horse is outside, it may be affected by various pests, including bot flies. These flies are a common problem for horses. Our vets at Mount Vernon can tell you about the symptoms of bot fly infestation in horses and how to prevent it.

What Are Bot Flies?

Bot flies may not be the most harmful parasites for horses, but they can still make them very uncomfortable, both inside and outside their bodies.

The main source of irritation from bot flies is external. These flies are quite large, and their main objective is to lay eggs in the horse's body hair. Although they do not bite horses, their landing and egg-laying activity causes irritation as they move around on the horse's body.

Types of Bot Flies

Here are the three types of bot flies we see on horses:

Common Bot Flies

The eggs of common bot flies are yellowish-gray and are usually attached to the tips of the horse's hair where the horse can scratch or groom them.

When the eggs hatch, the larvae move into the horse's mouth and then into the stomach, where they stay until spring. During this time, the larvae use hooks to attach themselves to the stomach's mucous membrane.

In the spring, the larvae are expelled with the horse's feces and then spend a month in dry soil before developing into adult flies. The female bot flies can lay around 500 eggs in a week, starting the cycle again.

Throat Bot Flies

Female throat bot flies also lay their eggs on horses, typically around the throat area. They lay around 500 eggs, similar to the common bot fly.

The larvae hatch within a few days and move along the horse's jaw, entering the mouth and settling in the gum line. This can cause discomfort for the horse as pockets form in the gums.

The larvae mature in the gums and then move into the horse's stomach for the winter, being expelled in the spring to begin their life cycle anew, just like the common bot fly.

Nose Bot Flies

Nose bot fly eggs are brownish-black and are typically laid in the hair around a horse's nose. These bot flies can be very irritating because they lay eggs one at a time and can lay around 160 eggs.

The eggs hatch within two days and burrow into the horse's lip and tongue. After 5 or 6 weeks, the larvae make their way into the stomach to continue their life cycle like the other types of nose bots.

Symptoms of Bot Flies in Horses

Some of the signs and symptoms of a bot fly infestation that may be noted in horses are:
  • loss of condition
  • impeded digestion
  • increased body temperature
  • restlessness
  • kicking at the belly
  • loss of appetite
  • intermittent diarrhea
  • constipation

It is also possible for bot flies to potentially cause more severe issues such as gastritis, stomach ulcers, and more rarely, peritonitis which is an inflammation of the membrane lining the abdominal cavity and can be fatal.

How to Treat Bot Flies in Horses

The life cycle of bot flies is about a year long, and breaking this cycle is important for successful treatment.

The initial step in the treatment process is to remove all bot fly eggs from the horse regularly, preferably on a daily basis.

Afterward, the horse must be treated with deworming medication to eliminate the larvae living in its stomach.

Your vet will be crucial in managing the timing and dosage of the medication to ensure effective treatment for your horse.

How to Prevent Bot Flies in Horses

One of the easiest ways to prevent bot flies in horses is through effective sanitation of the area your horse spends their time. 

Here are some of the things you can do to help reduce the possibility of bot flies infesting your horses:

  • Manure should be routinely cleaned up and properly composted. The heat generated during the process will kill the larvae of bot flies.
  • Proper pasture management, including frequent mowing and chain harrowing.
  • Utilize rotational grazing and if possible allow livestock to graze a pasture between horses.
  • Avoid feeding your horses from the ground.
  • Water Clean water, free of feces contamination, should be provided year-round.
  • Monitor your horse and keep up with egg removal as they are spotted.
  • Ensure that you keep your horse on a regular deworming program to minimize risk.

It is also recommended that you have fecal exams performed on your horse regularly to monitor for signs of any parasitic infections, including bot flies.

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.

Have you noticed the signs of bot flies on your horse? Book an appointment with our Mount Vernon vets today to discuss treatment and preventive measures. 

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