TALL FESCUE – Endophyte/Animal Relationships:

Tall fescue is a adaptable perennial grass used for livestock feed, various turf purposes and for erosion control. Tall Fescue is easy to establish and tolerant of a wide range of management regimens as well as a good forage grass. Tests done in laboratories compare favorably with other cool season grasses.

In the 1970’s the discovery of the endophyte fungus effects on grazing animals and the grass itself, attitudes towards Tall Fescue have changed significantly. This section is to explain the options for livestock producers have for using this important grass.


Tall Fescue has many attributes, but there are three livestock disorders that are associated with it. Here are some brief descriptions.


“Fescue Foot” is a dry, gangrenous condition of the extremities of the bodies of cattle consuming Tall Fescue. Typically it will causes lameness or the loss of the tips of tails or ears, but may result in sloughing of hooves and feet. Animal weight gains are also reduced. “Fescue Foot” is generally associated with cold weather.


Reproductive problems of mares grazing fescue have been widely recognized. These problems include: abortions, prolonged pregnancy, foaling problems which can result in foal and/or mare deaths, thick or retained placentas and poor milk production.


On-farm observations and research have provided evidence that cattle prefer endophyte free Tall Fescue. Tennessee, steers preferred for clover in endophyte infected pastures, but there were indications that they preferred Tall Fescue to clover in endophyte free Tall Fescue pastures. Heifers in Missouri were given a choice of diets containing 60% Tall Fescue endophyte free Tall Fescue or 75% endophyte infected Tall Fescue, 11 of 12 heifers avoided the endophyte infected diets. Much, but not all of the reduction of live stock average daily gain or gain per unit area of land on endophyte infected Tall Fescue is due to reduced feed intake.

Typically, physical factors suck as high fiber content are associated with poor intake, but they do not explain intake differences between endophyte free and endophyte infected Tall Fescue. The toxicants do appear to have a major effect on ruminal microbial digestion. Digestibility and crude protein content are similar in endophyte infected and endophyte free Tall Fescue.


  1. Reduced feed intake
  2. Lower weight gains
  3. Decreased milk production
  4. Higher respiration rate
  5. Elevated body temperature
  6. Rough hair coats
  7. More time spent in water or in shade
  8. Less time spent grazing
  9. Excessive salivation
  10. Excessive blood serum prolactin levels
  11. Reduced reproduction performance.


Endophyte toxicosis is commonly referred to as “summer syndrome” or “summer slump” because signs are most prevalent in hot weather. However, poor weight gain on endophyte infected pastures can occur throughout the grazing season.

Through air temperature, humidity, presence of other forages and animal management are known to have an influence, steer average daily gains has been shown to decrease approximately 0.1 lb for each 10% increase in infection rate.


The tall fescue in the United States is primarily used for commercial beef cow-calf operations. In several studies, cows grazing endophyte infected tall fescue lost weight and had lower pregnancy rates, and their nursing calves had much slower weight gain and reduced weaning rates compared to those grazing endophyte free tall fescue pastures.

FACT: a decline in body condition can affect reproduction, and cows that are thin before and at calving have a long interval between calving and first estrus.

Therefore; cows going into the breeding season in poor or a negative weight gain condition because of endophyte infected tall fescue will most likely have a prolonged post-partum interval regardless of later endophyte effects.

Supplementary feed in the form of either clover or grain for cattle on endophyte infected Tall Fescue improved pregnancy rates, but not up to economically acceptable levels. It appears that factors other than nutrition are involved in the reduced pregnancy rates associated with endophyte infected fescue.


  1. Establish new Tall Fescue stands – The optimum approach is to plant tall fescue in late summer/fall, then plant clover in late winter or the following late summer/fall. (Legumes may dominate endophyte free tall fescue if planted at the same time). White clover, seeded at 1 to 3 pounds per acre is the best legume companion in most fescue pastures. However, red clover, at a rate of 10 to 15 pounds per acre broadcast or 8 pounds per acre drilled is good especially when fields are to cut for hay. Birdsfoot trefoil, alfalfa may also be used as a fescue companion.

A. If you are unable to establish a new stand – it is highly recommended that a legume is planted with the endophyte infected grass.


  • Where you already of endophyte infected pastures, the existing stand should be tested by a laboratory to determine the amount of infection. Contact county extension services for information on cost, methods and labs in your area.
  • Once the endophyte levels have been determined, a producer can better determine the best option for dealing the endophyte infection problem. Four general approaches are available:
  1. Manage to minimize effect: Grazing and/or clipping management that keeps plants young and vegetative will result in better performance of livestock. Likewise, if endophyte infected fescue is cut for hay in the boot stage better animal performance will be obtained than from late cut hay.
  2. Avoid endophyte: Use of other forage grasses or legumes avoids the endophyte. Using endophyte infected tall fescue in spring and use of other grasses or grass-legume mixtures for grazing during the summer will avoid the endophyte during the summer when fescue forage quality is low. Feeding another type of hay may also be helpful.
  3. Dilute the endophyte: Use other feeds in the livestock’s diet. Using legumes in the endophyte infected pastures is a very attractive option. Many studies show greater live weight gains, and improved (though sometimes still unacceptable) pregnancy rates when pastures are renovated to include legumes.
  4. Kill infected stands and replant: endophyte free tall fescue is now readily available. Endophyte infected fields that are going to be replanted should not be allowed to go to seed allowing volunteer endophyte infected plants to establish.


  • Rotation: Rotate with other crops, followed by seeding of endophyte free seeding, is a excellent approach.
  • Prepared Seedbed: Destroy the old seed bed by tilling and then replanting endophyte free tall fescue. However, it is difficult to completely destroy an old fescue sod by tillage.
  • Chemical Till No-Till: Where methods 1 and 2 are not feasible, chemical kill of endophyte infected tall fescue followed by seeding of endophyte free tall fescue without tilling is the only remaining option. With this option it is critical that chemicals be used effectively – killing all existing endophyte infected tall fescue. Take into account other grasses that may be in the field requiring different amounts or different types of herbicides to kill. Best results for no till chemical kill have been found with late summer or early fall seedings of tall fescue, except in the northern tall fescue belt where spring seedings are feasible. Although chemical kill has been satisfactory in spring, summer drought and weed competition often reduce stands of spring seeded tall fescue.

TALL FESCUE/Endophyte and pregnant mares:

Understanding why tall fescue has the potential of either causing devastating foal losses or of providing safe, inexpensive nutrition for horses.

Problems identified with endophyte infected tall fescue:

  • Abortions: Abortions frequently happen with mares grazing infected tall fescue, usually in late gestation.
  • Prolonged Gestation: Mares may carry a foal for 370 days or more as opposed to the normal 336 day average gestation time.
  • Dystocia (Difficult Birth): Excessive size of foals due to increased gestation time often causing foaling problems.
  • Thick Placenta: Abnormally thick and/or tough placentas are often associated with mares grazing on infected tall fescue.
  • Foal Deaths: Many foals die during birth due to the problems associated with dystocia.
  • Retained Placenta: Associated problems are uterine infection, laminitis, septicemia which can cause the mare to be difficult to rebreed.
  • Agalactia: Lack of milk production is also associated with mares grazing on endophyte infected tall fescue. This can result in the starvation and weak foals. Colostrum production, and thus the transfer of antibodies may or may not be affected.
  • Mare Mortality: Complications associated with dystocia and retained placenta, sometimes result in the death of mares.
  • Difficulty in anticipating birth: The normal visual signs of impending birth such as udder development, swelling of the vulva, or other signs that birth is imminent are often not exhibited.

Definitive Study

“An experiment partially funded by the American Quarter Horse Association and initiated at Auburn University in 1986, appears to have convincingly established that the endophyte is indeed responsible for the reproductive difficulties of horses grazing tall fescue. The classic nature of the results justify discussion of this experiment in some detail.

Four research pastures of 11 acres each were established on a College of Veterinary Medicine unit at Auburn, Alabama in fall, 1986. Two of these pastures were endophyte-free, while the other two had over 80% endophyte infection. Once the pastures were established, nitrogen was applied in February and again in September at a rate of 100 pounds per acre application.

Twenty-two mature mares (6 Thoroughbreds, 8 Quarter Horses, 7 Arabians, 1 Morgan) wre bred on synchronized estrouses cycles from June-August, 1987. After pregnancy had been confirmed by palpation, the mares were randomly placed on either infected or non-infected fescue pasture on October 1, 1987.

The mares remained on the same fescue pastures through foaling, and during immediate postpartum period. During periods of inadequate fescue growth in winter, infected or non-infected fescue hay was fed in accordance with the status of the pasture to which the mares had been assigned. This hay was produced in fields planted at the same time and from the same seed lots as the research pastures.

Of the 11 mares foaling on the infected pastures, 10 had obvious clinical dystocia (foaling problems). In addition, four of the mares on these pastures had to be euthanatized (humanly destroyed), two because of serious uterine rupture, one because of unresponsive posterior paralysis, and one because of complications with a Caesarean section.

In addition, the endophyte severely affected foal survival. Of the 11 foals whose mothers were exposed to the fungus, only on survived the natal period. Three died soon after birth; one died during delivery; another survived for several hours but was euthanatized when it did not respond to routine nursing care; and a third lived for seven days but did not respond to aggressive nursing care and succumbed to septicemia despite plasma transfers and supportive care.

Of the seven stillborn foals first observed during assisted labor, death apparently occurred during parturition. Furthermore, in 10 of the 11 mares on infected fescue, there was no evidence of udder development or lactation prior to and through parturition. By contrast, all mares on non-infected fescue had normal births, all mares produced normal quantities of milk, and all foals survived.” (Oregon Tall Fescue Commission).


Horse producers have clear options to avoid having problems from this fungus. The logical step for many producers having broodmares is to eliminate existing infected fescue. Fescue can be killed with an herbicide labeled for this use, or with tillage(not highly recommended).

Once the infected plants are dead, the pasture can then be replanted. A very critical point is to be absolutely certain that the old endophyte infected sod is dead. It is very difficult to kill fescue in an old, established sod with tillage alone. Tillage also had the disadvantage of potentially creating a severe erosion hazard (experience of many producers is to avoid this route).

It is recommended to plant an annual forage or some row crop for at least one growing season prior to replanting endophyte free tall fescue. There are several benefits to this:

1. It reduces the likelihood that insects in the old fescue sod will damage the fescue seedlings

2. Reduces chances of infected seed already in the soil from infecting the new crop.

Dilution with legumes or other grasses does not work for horses. Where it seems to be somewhat effective for cattle, horses are more sensitive to the fungus and dilution is not effective.

Removal of Mares: Pasture with as little as 5% to 10% infected tall fescue should be removed from the pasture no later than 90 days prior to foaling. A study at Clemson University should however, that removal even 30 to 45 days prior to gestation greatly reduce the likelihood of reproductive and lactation problems.

Endophyte infected hay: infected hay remains highly toxic to horses as well. However, endophyte free fescue hay is excellent or horses. It is very difficult to obtain hay know to be free of the fungus.