UK Researchers Warn That Recent Weather Could Be Problematic for Mares Grazing Tall Fescue Pastures

According to researchers at the University of Kentucky Martin-Gatton College of Agriculture, Food and Environment, Kentucky’s late summer drought, followed by mild/late fall weather and recent rains could put mares at risk on tall fescue pastures.

In a statement jointly issued by Megan Romano, specialist veterinary toxicologist at the UK Veterinary Diagnostic Laboratory (VDL); Krista Lea, research analyst and coordinator of UK’s Horse Pasture Evaluation Program; Emma Adam, research and industry liaison and assistant professor with UK’s Department of Veterinary Science; and Ray Smith, extension professor and forage specialist within UK’s Department of Plant and Soil Sciences, horse farm owners and managers were advised on the following.

Important observations:

  • Recent rains after extended drought have enhanced endophyte-infected tall fescue production of the toxic compound, ergovaline.
  • Owners should restrict exposure to ergovaline in late-term pregnant mares to avoid tall fescue toxicosis. Signs of tall fescue toxicosis include poor or absent milk production; poor udder development; prolonged gestation, greater than two weeks; thickened, retained placenta; “red bag” deliveries; and potentially fatal dystocia/foaling trauma.
  • November and December are typically low pasture growth months where low ergovaline levels are seen, however the UK VDL recently tested numerous tall fescue samples and detected high ergovaline levels. Often fescue is diluted with other grasses, but recent weather conditions have allowed fescue to grow while bluegrass and orchardgrass have slower growth or are dormant.
  • This is an issue that can affect states beyond Kentucky. The “fescue belt” includes 50% or more of the acreage in the states of Alabama, Arkansas, Georgia, Illinois, Indiana, Kansas, Kentucky, Maryland, Mississippi, Missouri, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee, Virginia and West Virginia.

Protective measures:

  • Removing mares 60-90 days from their due date from pastures containing more than 20% toxic tall fescue onto pastures containing mainly orchard grass, Kentucky bluegrass or novel endophyte fescue.
  • Feeding appetizing, high-quality hay, such as alfalfa or alfalfa mixed hay, can dilute the intake of ergovaline eaten on pastures, reducing the risk in situations where moving mares to very low fescue pastures is not feasible.
  • Discussing managing high-risk mares and using domperidone with a veterinarian.
  • Once temperatures drop into the high teens, ergovaline usually drops for the remainder of the winter.

UK resources:

  • Owners can test pasture samples for ergovaline at the UK VDL. Samples can be collected using the instructions found here.
  • Local county extension agents can assist with sampling and results interpretation. Find your county extension agent here.
  • Learn more about tall fescue, including mitigation strategies and new novel endophyte tall fescue varieties with no ergovaline, by visiting the Alliance for Grassland Renewal.
  • Attend UK’s Equines and Endophytes Workshop Jan. 31 in Lexington. Register today at .

Editor: Holly Wiemers,

Image available on request. Photo credit to Jimmy Henning.

View release online:

The Martin-Gatton College of Agriculture, Food and Environment is an Equal Opportunity Organization with respect to education and employment and authorization to provide research, education information and other services only to individuals and institutions that function without regard to economic or social status and will not discriminate on the basis of race, color, ethnic origin, national origin, creed, religion, political belief, sex, sexual orientation, gender identity, gender expression, pregnancy, marital status, genetic information, age, veteran status, physical or mental disability or reprisal or retaliation for prior civil rights activity. 

Megan Romano,
Emma Adam, emma.adam@uky.ed
Ray Smith,
Krista Lea,