Fescue Toxicosis

Almost everyone that owns a horse is aware that the endophyte-containing tall fescue variety, Kentucky 31, and pregnant horses (or any breeding animal for that matter) don’t mix, but few people know why.  Kentucky 31 tall fescue is the most commonly grown fescue type in North Carolina.  It has been used as a forage for over 50 years and is one of our most hearty and resilient grasses.  It is a cool season, perennial grass that is resistant to drought, overgrazing and is quite nutritious.  It is also one of the most commonly used grasses for soil stabilization due to its extensive root system.  Unfortunately the property that makes the grass so hearty is also what affects the animals that graze it.  Kentucky 31 contains an endophyte fungus that causes the grass to survive and thrive where most other grasses would not, and also causes vasoconstriction along with many other health issues in the animals that eat it.  The constriction of blood vessels can cause poor thermoregulation (including heat stress), loss of limbs due to poor circulation, low feed intake and rate of gain, low birth weight and weaning weight, birthing problems, poor reproduction and poor milk production in all livestock species.  

In pregnant mares there are a whole host of reproduction related problems that are caused by fescue toxicosis.  Abortions may occur around the time the mare is expected to foal.  She may have a prolonged gestation period, sometimes by as much as 30-40 days, which can cause major birthing issues due to the foal continuing to grow over the extended period.  Thickened placenta and retained placenta can be caused by fescue toxicosis.  Most commonly however, is agalactia, or poor milk production, as previously mentioned.    

These are obviously major issues that we want to avoid, so most farms with broodmares either avoid fescue all together or do their best to manage their livestock on it.  Replacing toxic fescue with a novel-endophyte fescue is the most recommended management tool.  In the past, it was recommended to replace the Kentucky 31 with an endophyte-free variety of tall fescue, but since the endophyte is what makes the grass so great, in recent years there have been several different varieties of tall fescue developed that contain an endophyte but not the endophyte that is toxic; we call this novel-endophyte fescue.  This gives us the best of both worlds, a hearty, nutritious grass that we do not have to worry about letting our animals graze.  Converting your toxic fescue pastures to novel-endophyte pastures is a long term project, but can be accomplished relatively easily.  Contact your local extension office or Soil and Water office to find out how to get started.  If completely renovating your pastures is not something that seems like an option for your farm, dilution can make a difference in toxicity levels.  You can dilute the Kentucky 31 by overseeding with legumes or another cool season grass such as Orchardgrass or Brome.  This will at the least cut down on the amount of toxic fescue that your horse in ingesting.  The last management tool is to simply remove the pregnant mare from the tall fescue pasture during the last 60-90 days of gestation.  This means either putting her on a pasture composed of another grass type or dry-lotting her.  In either case she should be closely monitored for signs of fescue toxicity.

If you think you may have fescue toxicity issues on your farm you should contact your vet immediately.  Getting a management plan together by working with your vet and your local extension agent is key to finding what will work best for your farm.