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Fungus threatening forage, cattle health

Jeff Caldwell 07/14/2013 @ 9:08am Multimedia Editor for Agriculture.com and Successful Farming magazine.

If grazing cattle is a key part of your business, you've already felt enough pain in the last year. Now, add another challenge to your list.

The fungus ergot has been popping up in pastures around the Corn Belt this summer. It's been just about the perfect year for it: a wet, cool spring followed by seasonably hot summer temperatures. Ergotism, the infection of the fungus, could also be aided by what is likely to be a later-than-normal window for forage harvest because of the spring conditions, according to Iowa State University (ISU) Extension beef veterinarian Grant Dewell. And the fungus doesn't play favorites.

"Delayed harvesting of grass hay because of rain also means that late-cut hay may also be at risk of ergotism. Historically, rye was commonly affected by the ergot fungus but wheat, barley, oats, brome, fescue, blue, Timothy, and other grasses can also be infected. All animals are susceptible to ergot but cattle are often most affected," according to a report from Dewell and ISU veterinary toxicologist Steve Ensley. "The fungus produces toxic compounds called ergot alkaloids. The type and quantity of toxic alkaloids varies depending on the specific fungus that is infecting the plant, type of plant, and the environmental conditions. Therefore, risk of poisoning and the specific clinical signs will vary depending on specific conditions where the cattle are."

The primary symptom of ergot poisoning is the constriction of small arteries that can lead to rough hair coats, weight loss, and gangrenous symptoms in the legs and tail. Cattle feeling the latter may spend extended periods of time in standing water, and lameness in the hind limbs can ultimately occur.

"Gangrenous ergotism (synonymous with fescue foot) is also a result of vasoconstriction in the legs and tail. Gangrenous ergotism is often associated with cold temperatures but can be seen in the summer also," according to Dewell and Ensley's report. "Initially, cattle will be lame, usually in the hind limbs first. Swelling at the coronary band develops, and the animal will eventually slough its hoof wall if not removed from the ergot alkaloid in time. Necrosis of the tail and ears can also occur."

In both beef and dairy cattle, agalactia, or decreased milk production, can be a symptom of ergotism, too. This symptom is similar to the effects on milk output resulting from fescue toxicosis.

"Treatment of ergotism is primarily focused on removing the animal from the source of the ergot toxins. Animals can recover if they are removed early enough before severe clinical signs are present," Dewell and Ensley say. "However, once gangrene has begun, there is little that can be done."

What to look for

Identifying whether you've got an ergot problem is as simple as taking a close look at grass seed heads. Look for dark brown, black, or purple spots within heads, or full seed bodies that have changed to one of these darker colors. The discoloration indicates the seed tissue has been completely replaced.

"The fungus produces a mass called the sclerotia that completely replaces the ovary tissue of the plant and is often larger than a typical seed. These sclerotia will eventually fall to the ground and overwinter," Ensley says (see image at right, courtesy ISU Extension). "Pastures that have been severely affected would need to be plowed deep enough that the sclerotia are greater than 1 inch deep to prevent germination."

The best thing to do to keep the fungus from rampaging your herd is remove the animals from infected pasture as soon as possible. Though there's not a whole lot you can do once ergotism has become symptomatic to a severe degree, keeping the animals from consuming more of the toxin can prevent major damage. It's also important to make sure you're not inadvertently transmitting the fungus through haying.

"Grass in pasture or hay should be monitored regularly to determine if the ergot sclerotia is present. Many animals will go off feed or seek other grass that is not infected with the ergot fungus. However, cattle are known to selectively graze the seed head and are more at risk than other animals on pastures," Ensley says. "Cattle should be removed from pastures that have ergot sclerotia present. Since the ergot fungus is only in the seed head, grazing of infected pasture before the seed head develops is advised. Grass that has developed a seed head can be clipped before allowing cattle to graze. Hay produced from ergot-infested grass may be toxic as well. Often the sclerotia will drop off of the grass as it is being handled, but hay should be inspected to make sure that it does not contain sclerotia."

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