Page 1063 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

VetBooks.ir Chapter 70

Ergot and Fescue Toxicoses

Ramesh C. Gupta, Tim J. Evans and Steven S. Nicholson

INTRODUCTION Clinical disease associated with Claviceps has a parallel
in fescue grass toxicosis where gangrenous ergotism, hyper-
Ergot is a general term that applies to all species of the
thermia, production loss in cattle, and adverse effects on
fungus Claviceps. Ergotism refers to the disease conditions
reproduction and lactation in horses are similar (Evans et al.,
associated with long-term ingestion of toxic levels of ergot
2004a,b, 2012). The seeds of fescue grass can be infected
by animals and humans. Ergot contaminated rye (Secale
with C. purpurea but the ergot alkaloids of fescue grass
cereale) used as flour was responsible for episodes of
toxicosis are produced by the endophyte (endo5 within;
human ergotism in Europe during the Middle Ages. phyte5 plant) fungus Neotyphodium coenophialum.
Significance, chemistry, and determination of ergot alka-
Today, it is believed that greater than 95% of fescue
loids were reviewed by Krska and Crews (2008).The
pastures containing mostly Kentucky 31 variety are
genus Claviceps includes very specialized fungi that para-
infected by the endophyte, N. coenophialum. The tall fes-
sitize the flowers of grasses and cereal grains with no other
cue plant and its endophyte enjoy a symbiotic relation-
part of the plant infected. Ergot alkaloids produced by
ship, each benefits from the survival of the other. The
Claviceps cyperi in nutsedge was described as a toxicant in
plant supplies required nutrients to the endophyte. The
dairy cattle (Naude et al., 2005). Claviceps africana ergot
endophyte generates multiple toxins that are distributed
in sorghum produced dihydroergosine (DHES) and related
throughout the plant, thereby making the plant more resis-
alkaloids, which caused hyperthermia in cattle but dilution
tant to drought, insects, parasitic nematodes, fungi, and
in ensilage reduced average concentrations of DHES to
herbivores (Evans et al., 2012). Ergot alkaloid induced
approximately 1 mg/kg, a relatively safe level for cattle
fescue toxicosis has been studied in much more detail
(Blaney et al., 2010). This chapter primarily addresses
than has ergotism from ingested C. purpurea sclerotia. A
alkaloids produced by Claviceps purpurea and the various
similar endophyte fungus (N. lolli), containing ergovaline,
toxic effects, called ergotism, that are produced in animals
has been found in perennial and annual rye grass and has
and humans. The source of exposure for animals includes
been associated with clinical toxicosis (Bourke, 2003;
ergot-infected grains in feeds such as barley, rye, wheat,
Schneider et al., 1996). This chapter describes ergot and
and oats as well as infected seeds in forages consumed
fescue poisoning in animals.
while grazing or in hay and silage. Removal of ergotized
seeds along with broken grain kernels and debris by the BACKGROUND
process of mechanical screening of harvested and stored
grain concentrates the ergot in the screenings. Utilizing C. purpurea has a host range exceeding 200 species of
such contaminated grain screenings for human food or ani- grasses. It is distributed worldwide in temperate climatic
mal feed would create a distinct hazard. zones. During infection by C. purpurea, the ovary of the
Clinical syndromes include gangrene of the extremities grass seed or cereal grain is replaced by fungal mycelia.
of cattle and horses; hyperthermia and production loss in A sticky exudate known as honeydew is produced that
cattle; agalactia and abortion in swine; and agalactia and contains conidia, which can be transferred to infect other
other reproductive effects in mares. Most countries have a seeds. The honeydew hardens to form a hard brown,
regulatory limit of 0.1% 0.2% ergot in flour. The sug- purple or black compact mass of fungal tissue called a
gested maximum level for safety is 0.05%. In the United sclerotium (Fig. 70.1). The ergot bodies or sclerotia con-
States, wheat and rye with 0.3% sclerotia are considered tain up to 1.2% dry weight of toxic alkaloids (Burrows
unsafe, and oats, triticale, or barley having more than 0.1% and Tyrl, 2001). Sclerotia of most Claviceps species are
sclerotia are deemed unfit for human consumption. one to four times larger than the host seed and are readily
Veterinary Toxicology. DOI: http://dx.doi.org/10.1016/B978-0-12-811410-0.00070-2
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