Grain Mites in Horse Feed

Have you ever had the following situation happen to you? You go out to feed your horse and notice a fine dust on the outside of the feed bag. You look closer and realize the dust is moving! Yes, you can see all those little bugs bustling about, in search of food and other little bugs to reproduce with. Yuck! Where do they come from? Is the feed safe to give to your horse? Can they harm you?

Magnified image of grain mites

It turns out that these little critters are grain mites (Acarus siro L). Grain mites are common and exist in all grains, but only thrive and appear when the conditions – temperature and humidity – are just right for reproduction and growth. Their ideal environment is warmer than 77 degrees F, and over 85% humidity. Hence, you would have more problems with them in the warmer months of the year. Temperature changes, condensation, and poor ventilation may produce areas with enough moisture to encourage mite infestation.

If you have infested feed you should not feed it to your horse. These mites can contaminate the feed with allergens and can also transfer nasty germs. Infestation can negatively affect palatability and when animals are fed infested products the results can be decreased intake, inflammation of the intestines, diarrhea, impaired growth and allergic reactions. The good news for you personally is that these mites do not bite humans.

To help reduce your incidence of mite outbreaks:

  • Store your feed in a cool, dry place
  • Use your oldest feed first
  • Keep no more than a two week supply of feed on hand (especially in hot weather) to ensure freshness
  • If you store your feed in a container, clean it regularly between fillings to prevent buildup of fines
  • Keep your feed area clean and neat
  • Air movement, such as from a fan, can help prevent outbreaks

If you do have an outbreak in your feed room, remove affected feed from the room immediately and thoroughly clean the area. Pyrethrin can be applied to the area with a hand held fogging machine or aerosol spray can.

15 thoughts on “Grain Mites in Horse Feed

  1. The best feed bin I have used is an old (but not rusty) chest freezer. I find them at used appliance stores . I cut the broken compressor out of them so it is not so heavey. They are insulated and have a sealed lid which stays open while you scoop out your feed and closes easily. My feed stays cool in the summer and does not get hard (sweet feeds) in winter. Bugs and mice stay out and my feedroom floor stays cleaner. A fifteen cubic foot chest freezer will hold ten bags of feed and a seven cubic ft. Chest holds four bags of feed. I also like to divide them into two or three sections using strips of trim and 1/4inch finished plywood (no splintrrs). The interior is smooth and easy to clean. I use a square plastic scoop to get the last pieces of feed out in each section before I pour fresh feed in.

  2. Pingback: Grain Mites in Horse Feed | The Feed Room | Texas Horse Report

    • Hello Vicki,

      Interesting question! There is some information available about feeding squash to horses. Appears that there is nothing toxic about squash, pumpkins or melons as long as they are introduced gradually and fed in moderation. Also must not be fermented or moldy.

      Like any feed, best not to introduce too much at one time or overfeed. You may also want to consider getting the squash analyzed for nutrient content if you are introducing it as a major dietary component to ensure that your horse’s diet is balanced. If it is used as a low volume treat, analysis is less important.

      There is some indication that raw potatoes & vines are not recommended. Also, cruciferous vegetables are not recommended. Do not get your horse hooked on broccoli, kale, Brussels sprouts etc.

      Roy J.

  3. I might have grain mites…. My feed bags are very dusty looking and it is very dusty by the seams of the bags as well. What should I do with those bags? I do get rid of grain mites?


    • Hi Stacey,
      Great question! First, I would make sure that what you are seeing is, in fact, grain mites. If you watch the dust closely do the particles move? If it’s mites you should be able to see them crawling around. You may want to grab a magnifying glass and check to make sure that it is mites and not just dust. If you do find that these are mites we recommend that you do not feed it to your horses for the reason listed in the article, including digestive upset and allergic reactions. Instead, dispose of the feed and clean your feed storage area completely by sweeping up any stray feed particles, and cleaning every nook and cranny that the bugs could reside in. You may also want to spray the area with a bleach/water mixture. Start over with a fresh bag of feed and keep a limited supply on hand to help stop infestations of mites – usually a two week supply is recommended, especially in hot and humid conditions.
      Hope this helps!

    • Hi Madeleine, thank you for reaching out. If you’ve already fed the feed, then all you can do at this point is keep an eye on his health and behavior. If you see anything unusual, contact your vet immediately.
      Thank you ~ Gina T.

  4. Our daughter had her horse feed in the garage.
    during the December holiday we have noticed mites in the living area. It is a small hard little bugger. At first we thought it was fleas, but I tried to squeeze the little thing and it was so hard that I had to really press down hard.
    Can I presume that it is mites? Now they are in the house.
    We have cleaned the area, but I presume not to good as they will hide in cracks etcetera.

    How do we get rid of them? Is it a hazardous thing? Will these mites go into our clothes, cupboards etcetera. Please help as I am at my wits end.

    Thank you

    • Hello Marlize, Thank you for contacting us. Mites are generally harmless to people, pets, furniture, etc – they are simply annoying. Wherever they are, you can apply Pyrethrin spray with a hand held fogging machine or aerosol spray can. You may want to check with a local pest company for assistance or further guidance, particularly if they are in your kitchen area.
      Thank you ~ Gina T.

  5. It sounds like Marlize van Zyl may have something other than mites, they may want to check with a Pest Control specialist. If it looks similar to a flea it could possibly be bedbugs!

    • Hi Richard, While it’s unlikely that a single instance will do much, we recommend keeping an eye on your horse for 24-72 hours after the feeding, and if he displays any unusual symptoms, contact your vet immediately.
      Thank you ~ Gina

  6. Hello, I just bought a few bags of feed from my local feed store, after only 2 days of being at my house, I opened the bag to pour into my container and noticed a few clumps of moldy feed….there wasn’t too many clumps, but I don’t know how many is too many…is this ok to feed to my horse if I remove the clumps before feeding? Also, there is what appears to be a date on the bottom of the bag, and I think I’m reading 5 June 09 does that mean this feed was made in 2009 and is that old? how old is old? thanks!

    • Hello MC, Thanks for the question! When in doubt, don’t feed it! And in the case of mold, we would definitely recommend not feeding it. It would be better for your horse to simple go without grain and only eat hay for a day or two if you can’t get right back to the store for fresh feed, than to possibly consume moldy feed.

      As for the date on the bag, that is more likely from June 9th of 2015 than the other way around, but if you are unsure, ask your feed store to help you interpret the date to be sure. As for how long it is good for, feed does have a definite shelf life – it’s perishable just like milk or bread from the grocery store. Pelleted feeds last a little longer than sweet feeds since they are lower in moisture and thus less likely to mold, but we typically recommend using any feed within 3-4 months at most of the manufacture date. Vitamins and amino acids will start to break down after about 6 months. Ideally though, for optimum freshness and palatability, you would want to feed a product within 30 to 60 days, though.

      Hope that helps! Thank you ~ Gina T.

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