How horses are affected by tall fescue grass and endophytes


Is tall fescue grass dangerous for my horse, or is it only dangerous for pregnant mares. You may have heard that fescue grass is dangerous for pregnant mares. Yes, not necessarily, and also stallions, too.


jump to shopping


What do I need to know about fescue and horses?


  • Fescue grass is prevalent in the US because it’s hardy. It tolerates drought, it’s easy to grow, horses love the taste, it’s nutritious.


  • Fescue grass is a cool season, perennial grass. Cool season grasses, such as blue grass, orchard, canary, rye, fescue, and timothy do well in cooler climates. Think the northern portion of the US. Although, they might also do well in the southern US during the winter. Peak growing season is spring and fall.


  • Along with higher NSC values, cool season grasses typically have more calories and are more delicious for horses.


  • But, what makes it so hardy is the little fungus buddy growing INSIDE of it. The endophyte.


What are endophytes?


  • An endophyte is a fungus that grows within another plant. The host plant is unharmed by this freeloader, and in some cases, may be improved by the fungus.


  • The fungus that lives with fescue grass is Acremonium coenophialum. This fungus will make alkaloids as part of its life cycle, and the hosting fescue grass uses these alkaloids to ward off insects and worms. Good for the fescue!


  • And, since the fescue is now stronger, it can start to grow well even if the soil and growing conditions are not great.


The downsides to these endophytes.


  • This endophyte also likes to create some chaos in pregnant mares, foals, and even stallions. Seems the endophytes really like to interfere with the reproductive systems of horses and other grazing animals.


  • A pregnant mare can abort a pregnancy, or develop other complications such as prolonged gestation. This prolonged gestation, sometimes months longer, results in difficult births. Mares may also have an absence of milk, which leads to starvation of the foal. Retained placentas are also a risk, which leads to laminitis.


  • Foals, if they survive, can starve and are often weak and immature.


  • Stallions have been found to have reduced amounts of ejaculate volume, which of course will impact the bottom line on a breeding business.


gray horse in far corner of green grass pasture

A simple lab test can determine if your horse’s pasture has endophytes, and then any breeding stock you have can be properly cared for.


There is a medication available from your veterinarian if your pregnant mare is on endophyte-infested fescue.


  • You need to find out if your fescue grass also has endophytes. A simple laboratory test can test and confirm this for you. You will also need to know how far along your pregnant mare is.


  • You should also know that non-breeding horses are unaffected by endophytes in the fescue grass. So, if your barn is full of geldings and non-breeding mares and/or stallions you are ok.


zoomed in on fescue grass blades

Yum – delicious!


What do you do if you have endophytes in your pasture?


  • You do have the option of starting over in your pastures if you need to rid them of endophytes in your fescue grass. The best time to start this project is before your pastures go to seed. Mow the fescue before seed heads appear.


  • Then you can use herbicides several times a few weeks apart to eliminate the fescue completely. This is time-consuming, and you will be out of pasture for a bit. Then you can reseed with your pasture grass of choice.


  • You can also sprinkle in other grasses with the fescue to dilute the amounts of endophytes, but at some point, you will not be able to accurately guess how that is working for you, and a pregnant mare will still be at risk.


  • There are also endophyte-free fescue grasses available for pastures as well. There are also loads of other types of pasture grasses, some grow better in different climates.


  • Researchers in New Zealand have developed fescue grasses with horse-friendly endophytes. These strains of endophytes are beneficial to the fescue and safe for pregnant mares and stallions.


  • Your local agriculture extension service will be able to help you determine what’s in your pasture, as well as what could work better if you need to start from scratch!


horse lips chewing on fescue grass in pasture



go shopping button for horse products


Stock up here for your horse supplies! As an Amazon Associate, I earn from qualifying purchases, but it’s ZERO extra cents to you.  You can also visit my Amazon storefront here:  PEG storefront.

06/12/2024 11:53 am GMT
06/13/2024 02:43 am GMT
Jolly Pets Horsemen's Pride Amazing Graze Toy

Keep your horse's brain happy!

05/08/2024 12:48 am GMT

Great to use with buckets to discourage cribbing

04/10/2024 07:03 pm GMT
Equiessentials Slow Feed Hay Ball Large
$130.05 $120.20 ($120.20 / Count)
05/20/2024 02:22 pm GMT
05/30/2024 10:15 am GMT
Grazing Muzzle by GG Equine

Basket-style grazing muzzle to help keep a horse at a healthy weight and help reduce the risks of colic and laminitis in some horses.

Use code 15PROEQUINE for savings sitewide on muzzles, halters, slow feeders, and more.

HayPlay Slow Feed Bag XL – GG Equine

One side of this innovative slow feeder is solid - perfect for pastures! It will hold a small bale of hay.

Use code 15PROEQUINE for sitewide savings on slow feeders and more.

HayPlay Slow Feed Bag – GG Equine - 2 sizes available

2 sizes of this slow-feeding hay toy - snack size holds a few flakes, and the half size holds 1/2 bale.

Use code 15PROEQUINE for sitewide savings on slow feeders and more.

40 lb. Alfalfa Cubes
$35.02 ($0.05 / Fl Oz)
04/10/2024 06:48 pm GMT
04/10/2024 08:03 pm GMT


Thank you!