Pasture management tips to avoid plant toxicities

Although pasture management is usually associated with rotational grazing and parasite control, recognizing plants that can be toxic to livestock is sometimes even more important than overgrazing paddocks.

Jeffery Clark, pasture market development specialist at Corteva Agriscience, recently spoke at the National Cattlemen Beef Association Winter Reboot virtual convention Feb. 23 to 24, and detailed several plant toxicities ranchers should be aware of and how to manage their pastures to prevent illness or death in their herds.

“A good grazing management program is just as important as a good vaccine, feed and mineral program, however, the pasture management side of it is typically the last to be looked at,” Clark said. “We have many tools in the tool box, but probably the one that is the most important is managing those forages and taking care of those pastures.”

Some common toxic weed culprits in cattle are buttercup, white snakeroot and poison hemlock, which can cause anything from respiratory distress, trembles, milk toxins, lung tissue damage, blisters or gastrointestinal irritation. Another plant that causes cattlemen thousands of dollars each year is perilla mint.

Perilla mint contains ketones that cause acute respiratory distress syndrome in cattle, which is also called panting disease. Cattle only need to ingest a small amount of the plant to become ill and death can occur within 45 minutes. There is no remedy or cure for cattle that ingest this plant. Panting disease can be suspected when cattle stretch their necks out gasping for air and are frothing at the mouth. Fluid accumulates in the lungs, resulting in lower oxygen levels, shortness of breath and death.

“We see more problems with calves than cows because calves are more curious and more likely to sample plants they shouldn’t,” Clark said. “The plant can also attract calves because it has a minty fragrance. Once they lick it, it tastes good so they eat it.”

Perilla mint is an annual plant that grows in shade and sunlight. It is designed to germinate, grow, reproduce more seed and then that plant itself dies off. Clark said the easiest way to identify perilla mint, is by its wide leaf that is green on top and purple on the bottom. It starts to pop up in pastures typically around June.

Grass toxicities to recognize

Tall fescue, a perennial, is a good protein and total digestible nutrients grass, but usually in April issues start to arise with toxicity.

“Cattle love to eat fescue seed heads, and while in a vegetative state it has phenomenal value to a forage based program, the fungal endophyte in tall fescue produces alkaloids that are consumed by grazing animals,” Clark explained. “Alkaloids bind to the blood vessels, causing vasoconstriction and thus making thermoregulation difficult.”

Clark said although the alkaloids are low in the stem of the plant, they are extremely concentrated in the seed head. With fescue toxicity, cattle cannot cool off, therefore their body temperature goes up, leading to a decrease in grazing time as summer temperatures increase.

“When they should be out grazing, they’re in a pond or under a shade tree because they are trying to bring their body temperature down,” he said.

Because they are not grazing as much as usual, there is a reduction in body condition score and average daily gain decreases dramatically.

“If we’re dropping average daily gain, we’re going to have to be feeding a lot more than the standard 2.5 to 3.5 pounds per day per head,” Clark explained. “Anytime we start to see a decrease in daily gains, we have to pretty much assume it’s going to be a 45- to 50-pound loss on that calf at the tail end that we’re trying to get caught up on.”

When it comes to cows, Clark said research has shown that when 70% or more of the pasture contains toxic fescue, pregnancy rates decrease 15 to 40% and milk production decreases 25%. Weaning weights on calves decrease by 65 to 85 pounds, time spent on grazing decreases 20%, forage intake decreases 25 to 40%, average daily gain decreases by almost 1.5 pounds per day and body temperature increased 1 to 4 degrees.

Cattle that have fescue toxicity have a dull, sickly appearance, rapid weight loss, arched back, rough, scraggly hair in the summertime, partial to complete loss of hair from the end of the tail, gangrene of the extremities that can lead to loss of tail switch, ear tips and in severe cases, the feet.

“Probably one of the most famous things about fescue is fescue foot,” Clark said. “They’ll eat fescue in the spring and summer and then in the fall, cows start developing foot problems. They’re sore, they can’t really stand on them, there is a lot of redness around the coronary band and they want to lay around a lot.”

There are two ways to control fescue toxicity in pastures—herbicide or mechanical means. Clark said ranchers need to be out in the fields by beginning to mid-April looking for the flag leaf stage.

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“Once we see the flag leaf, we know the boot is there, which means the seed head is at the prime spot for us to spray it and eliminate the seed head and make it to where we have a vegetative, grazable, safe grass,” he said. “I’m not a fan of mechanical mowing because we can really do even more damage to our pastures by mowing the desirable part of the plant cattle could be eating that is high protein.”

Another grazing forage that can turn deadly if not managed properly is dallisgrass. Known for preventing erosion, dallisgrass was one of the first grasses to be introduced in a pasture grazing segment of the forage business. It is a perennial bunch grass that is well adapted to the southern United States. Dallisgrass has a low seed germination, which causes slow establishment, unlike fescue that puts out a bunch of seed and grows rapidly. Typically found in sparse areas, primary forage is utilized for grazing, but can be harvested as hay.

Forage production typically occurs from April to October, but by the end of summer—between August and September—dallisgrass becomes dangerous to cattle. Similar to fescue, dallisgrass produces alkaloids that are consumed with the seed head.

“The seed head becomes infected with an ergot fungus and it creates a sticky substance at the mature time period,” Clark explained. “It leads to a neurological disorder called the dallisgrass staggers.”

Symptoms of dallisgrass toxicity include: aggressive behavior, collapsing, diarrhea, low average daily gains, jerking and unbalanced movements. Treatment for both fescue and dallisgrass toxicity are to remove the animal from the toxic field and provide plenty of hay, water and grain to flush the poison out of their system. Clark suggests making an appointment with an expert to do a pasture walk and identify any weeds that could prove problematic to livestock.

Lacey Newlin can be reached at 620-227-1892 or [email protected].