Vet's Perspective

Opinion
Oct 11, 2013
by WLJ

Ergot toxicity

 

 

Although much of the growing season had been dry and dusty, more recently we have been experiencing an excess of moisture in the environment. Very wet and humid conditions during peak growing season can result in ergot infestation on grass heads. Ergot is known to occur throughout the world and is endemic in the Great Plains region.

Ergot is a fungus with toxic potential to both livestock and humans when eaten in sufficient quantities. Poisonous mycotoxins are produced in place of the grain seed head and are the cause for toxicity. Fungal spores can survive on the soil surface or within the soil for a minimum of a year; when moisture and spring temperatures arise after a cool winter, the spores may germinate and be dispersed into the environment. The causative fungus in small grain is Claviceps purpurea. Affected grass heads are seen to be hard and dark in color; although early infection may be noted by the appearance of a yellow colored slime on the head of a plant soon after flowering. This “slime” has a sugary substance that invites insects to the plant and further perpetuates the dispersal of causative fungal spores.

Ergotoxine is the active toxin that stimulates the nerve centers and causes small blood vessel constriction, thereby blunting blood supply to various parts of the body. In humans, this illness has been termed “holy fire,” and has been debated to have played a part in the hallucinations during the Salem witchcraft trials.

The amount of ergotoxine required to cause toxicity can vary as the amount of toxin in each ergot kernel may vary due to species of Claviceps, type of affected plants and ambient conditions. Previous studies have shown a week of eating approximately three ounces of ergot kernels to produce lameness in cattle. Very small quantities ingested can allow recovery without symptoms.

Four main types of disease are noted in affected animals: gangrenous; hyperthermic; convulsive; and reproductive. Severe lameness results from a large quantity of ingested toxin, creating a dry gangrene in extremities due to oxygen-starved limbs and lack of adequate blood flow. The tissue of limbs, beaks, ear tips and tails may slough off and a rotten, foul odor is noted.

Animals can show hyperthermic illness by excessive panting and inability to regulate normal body temperature. This form of illness may appear similar to general respiratory disease.

Other noted symptoms in cattle may be a lack of appetite, dull behavior and abdominal pain.

Abortions can occur due to stimulation of uterine muscles and disruption of hormones necessary to maintain a full term pregnancy. Offspring that do survive may be ill thrift and unable to suckle as the dam cannot produce any milk.

A less common form of illness is the convulsive toxicosis. Animals typically have ingested a large amount of ergot in a short period of time and may demonstrate seizures and abnormal behaviors.

Affected plants can be found within pastures in which grasses are coming to a “head” stage in development. Most likely culprits are pastures and ditches that have not been mowed, or a cutting from pastures after the plant has begun to seed out. Common pasture and wild grasses that may become affected by ergotoxine are: brome grass, orchard grass, timothy, wild oats, wild barley, fescue, perennial rye grass, and quack grass. Any plant with a longer flowering period will tend to be more susceptible to infestation.

Diagnosis of ergot toxicosis is based off of clinical signs in affected animals and reported exposure to infected plants or grains. The most obvious sign is necrotic tissue in one or several exposed animals. Feeds can undergo chemical analysis for further confirmation.

No direct treatment is available for affected livestock and withdrawal times have not been established. Contaminated feeds and pastures should be removed; pastures should be mowed and let dormant for at least two weeks before grazing resumes. A recent report out of the University of Nebraska stated a potential cereal grain yield loss of five to ten percent in affected regions. Some ergots may be removed through specialized grain cleaning equipment. It may also be of benefit to purchase sclerotia-free seed when planting a subsequent cereal grain crop in affected areas. It is also recommended to mow grasses before they head if risk is high in your area. — Dr. Genevieve Grammer

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