Tall Fescue is the
predominant cool-season forage found in pastures across North Carolina,
particularly in the counties north of Interstate 40 and in the mountains. Most of this Fescue has been established for
a long time, and contains the endophyte fungus Acremonium coenephialum, sometimes referred to as toxic endophyte. Tall Fescue is a high-yielding forage that
takes abuse and keeps on growing, making it a good choice as a pasture grass
for livestock. However, there are also
problems associated with grazing fescue that horse owners need to keep in
mind. Those problems affect pregnant
broodmares, foals, horses that are pastured for long periods of time on Fescue
and not exercised, and – to a lesser extent – young, growing horses.
Since the major effect of
Fescue toxicosis is on pregnant mares, (and since this article focuses on
broodmares) let’s look at those problems.
Fescue toxicity is known to cause prolonged gestation (cases up to 30 to
40 days have been documented). Prolonged
gestation means that the foal is larger than usual when born, which in turn
means more instances of dystocia and difficult births. Endophyte has been implicated as a potential
cause of premature separation of the chorion and abortion in mares. Other problems include thickened or retained
placentas, which can lead to excessive hemorrhaging in the mare, which could
cause death. Uterine infections may increase, causing a delay in
rebreeding. If those problems weren’t
enough to deal with, the mare may have aglactia (no milk), and colostrum may be
reduced or non-existent. Since colostrum
carries antibodies needed by the foal to resist disease, the foal is more
likely to develop an infection of some kind.
While all the mechanisms
that cause the reproductive problems are not known, it is known that the ergot
alkaloids produced by the toxic endophyte act as dopamine. Excess dopamine suppresses the production of
the reproductive hormone prolactin.
Prolactin is essential to the final stages of pregnancy and birth. Progesterone levels are also suppressed. The levels of progesterone should increase
about two weeks before birth, but mares exposed to toxic endophyte have reduced
progesterone levels.
Management options to
avoid these problems include:
1) Having a forage test run
to determine if the toxic endophyte is actually present in pastures. If it is detected, then
2) Remove pregnant mares
from fields with endophyte-infected tall fescue 45 to 90 days before foaling
and feed them good quality hay and grain or put them on a pasture that is not
infected with toxic endophyte. This is
the most conservative way of avoiding toxicity problems.
3) Drug therapy has been used
to stimulate prolactin and progesterone.
Domperidone binds to the dopamine receptor and prevents the inhibition
of prolactin secretion. There is an
expense to this treatment. Consult with your veterinarian before taking this course of action.
4) Manage Fescue pastures to
minimize the effect of endophyte.
Grazing, clipping, or mowing pastures to keep Fescue in a vegetative
state helps keep the level of endophyte lower.
5) Avoid the endophyte. Use other species for grazing and hay.
6) Dilute the endophyte. Use other feeds in the diet. Grow legumes in with the Fescue. This dilutes the amount if endophyte
ingested, improves the quality of the forage, and reduces the amount of
nitrogen fertilizer needed for forage growth.
7) Kill infected stands and
replant. This is an extreme option due
to the cost and time it will take to accomplish, but this can be done. Dr. Matt Poore at NC State is gathering data
on doing this on his home farm – as a business decision and not an experimental
trial!
Tall Fescue has been and
likely will continue to be the most common pasture and hay forage used in many
parts of North Carolina. We should remember that not every mare displays the symptoms or problems that have been
mentioned. We need to remember that
mares have been grazing fescue pastures for a long time, and there have been a
lot of foals born with no problems on these pastures. However, research does show that there higher
instances of these problems occurring if pregnant mares are kept on endophyte
infected fescue for the duration of the pregnancy. Let’s be aware of the potential for problems
associated with Fescue and use one or more of the recommended strategies to
minimize the risk of any of these happening.
Here are some good
references for more information on Fescue Toxicity in Broodmares:
