Walking On Volume 6, Issue 8, August 2019 | Page 6

For the Health of It
Tall Fescues – Endophyte-infected,
Endophyte-free, and Novel Endophyte
Reprinted with permission from the January 2019 issue of Equine Disease Quarterly
Tall fescue (Lolium arundinace-
um) is one of the most widely grown
perennial grasses in the world and
covers approximately 37 million acres
in the United States alone. It can be
infected with an endophytic fungus
(Epichloë coenophiala), which in a
symbiotic relationship with the plant
produces chemicals called alkaloids
that confer benefits to the plant. This
tall fescue, native to Europe, was in-
troduced into the United States in the
1800s. In 1931, E.N. Fergus, a Univer-
sity of Kentucky agronomist, collected
tall fescue seed from the Suiter farm
in Menifee County, KY, on the basis of
winter hardiness, persistence in high
traffic areas, and drought resistance,
giving rise to the cultivar of fescue
known as Kentucky 31 (KY31). How-
ever, some of the alkaloids, primarily
the ergot alkaloids produced by infect-
ed plants, are detrimental to grazing
animals, including horses.
Historically, the endocrine hall-
mark of fescue toxicosis in several
animal species is a decrease in the cir-
culating concentration of the hormone
prolactin. Prolactin is secreted by the
pituitary gland, and control of its se-
cretion is complex and not completely
understood. Prolactin exerts effects
on a variety of systems including milk
production, steroidogenesis (estro-
gens, progesterone and testosterone),
hair growth and shedding, libido, and
synthesis of surfactant by the fetal
lungs. Importantly, prolactin may also
exert an effect on the feto-placental
unit by altering steroid synthesis and/
or metabolism and maturation of the
fetal adrenal-pituitary axis, which is
necessary for parturition. One major
regulator of prolactin secretion is do-
6 • Walking On
pamine, a hormone produced by the
hypothalamus. Dopamine, interacts
with receptors in the pituitary gland
and inhibits the secretion of prolactin.
Ergovaline is the most abundant er-
got alkaloid in tall fescue. Ergovaline,
and several other alkaloids from fes-
cue, have similar chemical structures
to dopamine and can bind to dopa-
mine receptors, thereby causing a de-
crease in prolactin secretion, resulting
in partial or complete agalactia (the
inability to produce milk) in foaling
mares. Additional problems associat-
ed with KY31 fescue consumption in
foaling mares include altered hormone
concentrations, extended gestation,
thickened placenta, placental reten-
tion, dystocia, birth of dysmature
foals, and increased foal and placental
weights. Dopamine receptors have
been found in tissues other than the
pituitary, including ovarian tissues
and the corpus luteum, but the roles
of those receptors in fescue toxicosis,
if any, have not been fully elucidated.
The drug domperidone is frequently
used in broodmares that are exposed
to KY31 fescue and prevents or revers-
es the adverse reactions of ergovaline.
Domperidone functions by binding to
dopamine receptors, but rather than
suppressing prolactin production, it
competes with dopamine and allows
for normal prolactin secretion.
Because of the adverse health
effects of common endophyte infected
fescue in grazing animals, varieties of
tall fescue which do not contain the
fungal endophyte have been identified.
Even though these endophyte-free
varieties do not produce ergot alka-
loids, animal performance is excellent.
However, the plants do not persist well
in pastures or compete well with other
pasture grasses. More recently, endo-
phyte strains that do not produce the
alkaloids that are harmful to animals
but still confer vigor and persistence
to the plant, have been identified and
inserted into tall fescue. These are
called novel endophyte varieties of
fescue, and some of these are com-
mercially marketed as “Jesup Max Q,”
“Texoma Max QII,” and “Baroptima
Plus E34.” More recently, “Lacefield
Max QII” was released by Dr. Tim
Phillips in the Department of Plant
and Soil Sciences at the University of
Kentucky. The Alliance for Grassland
Renewal is an association of seed com-
panies, universities, and government
agencies that regulate themselves by
establishing certain quality control
standards for novel endophyte tall fes-
cues. For example, all seeds sold under
the Alliance tag must be 95% pure,
have 70% live (viable) endophyte,
and have independent confirmation
that the fescue variety does not cause
fescue toxicosis in animals and will
persist well under conventional graz-
ing conditions.
Although this article emphasies the
effects of ergot alkaloids on a dopa-
minergic receptor, it is important to
remember that some of the alkaloids
also bind to other receptor types,
including adrenergic and serotonergic
receptors, and thus may affect addi-
tional body systems.
CONTACT:
Karen McDowell, PhD
kmcd@uky .edu | [phone]
Maxwell H . Gluck Equine Research Center
Tim Phillips, PhD
Department of Plant and Soil Sciences
University of Kentucky, Lexington, KY