Vasoconstriction & Heat Stress Caused By Ergot Alkaloids & Fescue ToxinsSaturday, October 22, 2011
Ergotism is one of the oldest known mycotoxicoses, with the first documented epidemic of ergotism in the Middle Ages, when thousands of people died because of the “holy fire”.
Ergot alkaloids (also named ergolines) exert toxic effects in all animal species, and the most prominent toxic signs can be attributed to the interaction of ergot alkaloids with adrenergic, serotinergic and dopaminergic receptors.
Information on the chemical and toxicological properties of individual ergot alkaloids is too limited at the present time for their selection as individual marker toxins when it comes to monitoring the extent of contamination. This means that neither the total alkaloid content, nor a single alkaloid can be recommended as reliable indicators of the potential adverse effects to livestock associated with the ingestion of ergot contaminated feeds. Alkaloids have different and dose-dependent receptor selectivity (binding affinity). Consequently, the biological effects of the various complex mixtures to which animals are exposed to, remain unpredictable.
The term ergot alkaloid refers to a diverse group of about forty different toxins which are formed by Claviceps spp. on grains (rye (see Figure 1), triticale, corn, wheat, barley, oats, millet, sorghum and rice) and by fungal endophytes such as Neotyphodium spp. in grasses, particularly tall fescue and perennial ryegrass, which adversely affects the health and productivity of livestock. This fungus produces the ergot responsible for the ergot alkaloid group of mycotoxins and parasitizes the seed heads of plants at the time of flowering.
Table 1: Classification of the main ergot alkaloid producing fungi
|Major classes||Fungi species||Mycotoxins|
|Ergot alklaloids: clavines, lysergic acid, lysergic acid amids, ergopeptines|
|Neotyphodium (form. Acremonium)||N. coenophialum||Tall fescue toxins (endophyte toxins): ergot alkaloids, lolines,|
|N. lolli||Tall fescue toxins (endophyte toxins): lolitrems, peramine, ergot alkaloid (ergovaline)|
The main groups of natural ergot alkaloids are:
- The clavines – e.g. agroclavine
- The lysergic acids
- The lysergic acid amides – e.g. ergonovine (ergometrine, ergobasine), ergine
- The ergopeptines – e.g. ergovaline, ergotamine, ergocornine, ergocristine, ergosine, ergocryptine
The ingestion of contaminated feedstuffs by the animals can have several sources ranging from contaminated farm equipment to contaminated seed line and feeding contaminated hay or silage. Therefore, good agricultural practices that limit contamination along with feeding compounds that have the capacity to bind these toxins are needed to reduce or eliminate the harmful effects. These selected substances bind ergot alkaloids in the gastrointestinal tract, reduce their bioavailability and increase their excretion as an adsorbent-toxin complex, thus helping control the negative impacts of these mycotoxins.
Ingestion of endophyte toxins in grasses, even at sub-clinical amounts is of concern in animal production. Perennial ryegrass endophytes (Neotyphodium lolii) together with the neurotoxin lolitrem B and the vasoconstrictor ergovaline are responsible for, among others, hypersensitivity in ruminants, impaired heat stress recognition, and vasoconstriction.
Plant toxins are chemical defense of plants against herbivores. Endophytic toxins in grasses include ergot alkaloids in tall fescue and tremorgens (e.g., lolitrem B) in perennial ryegrass. Perennial ryegrass endophyte (Neotyphodium lolii) alkaloids are frequently present in pastures containing the neurotoxin lolitrem B, together with the vaso-constrictor ergovaline, at levels associated with ryegrass staggers, heat stress, ill-thrift and lowered milk production. It has been shown that some of the physiological processes such as fertility may be lowered following ingestion of alkaloids produced by Neotyphodium endophytes.
Animals can be exposed to complex mixtures of ergot alkaloids in many typical animal agriculture production systems. This exposure results from the fact that the kinds of alkaloids present and their levels can vary widely, depending on the fungal strain, the host plant and environmental conditions, being impossible to relate the exposure to individual toxins.
The chemically diverse group of ergot alkaloids has been shown in vasoconstriction symptoms, being responsible for heat intolerance as well as necrosis of ears, tails and often hooves. Other symptoms such gangrenous changes, neurotoxic signs including convulsions, abortions and death, reduced prolactin secretion and consequently agalactia have been reported as major adverse effects in animals.
Due to the fact that animals are exposed to a multiplicity of alkaloids when consuming endophyte-infected tall fescue, a combined alkaloid effect has been suggested by Klotz et al. (2008). Chronic exposure to moderate amounts of ergot alkaloids results in reduced weight gain, low reproductive efficiency, including decreased conception rates, decreased circulating progesterone, and reduced signs of estrus.
Experiments conducted in New Zealand indicate that cattle are slightly less susceptible to ergovaline toxicity than sheep with respect to live weight gain suppression (Table 2).
Table 2. Biochemical criteria to diagnose potential ergot alkaloid toxicity
|Ergovaline intake (mg/kg LW0.75)||Sheep||>0.08||0.03|
|Pasture ergovaline (mg/kg DM)||Sheep||>0.9||0.03|
Mg/kg LW0.75: milligrams per kilogram of animal live weight
Mg/kg DM: milligrams per kilogram of dry matter intake
Threshold levels of ergovaline and lolitrem B have been established for cattle, sheep and horses (Table 3). These levels, however, refer to the level of toxin in the total diet, not in single feed components.
Table 3. Threshold levels of ergovaline and lolitrem B in the diet able to produce a clinical disease
|Ergovaline (ppb)||Lolitrem B (ppb)|
*Except for mares in the last 60 to 90 days of pregnancy, when the threshold is zero.
The use of high quality feedstuffs to reduce toxicosis of ergot alkaloids in livestock is the first step in avoiding problems they can cause, but to totally protect animals from the increasing risk of ergot alkaloid poisoning, a mycotoxin risk assessment is recommended.October 2011