Potentials for Plant and Other Toxicities in Cattle

While Johnsongrass is a good quality forage, it can be challenging to control in pastures where the perennial, warm-season grass is not desired. Prussic acid production under stress can pose a risk to livestock when grazing Johnsongrass, especially during prolonged droughts or after a frost.
( Dirk Philipp, University of Arkansas )

Fortunately, there has been plenty of rain this year. However, heading into late summer and fall are times of the year to watch out for plant toxicity in cattle.  In some cases, plants can become more toxic during drought and heat stress.  In addition, there is the increased potential for cattle to ingest toxic plants due to lack of other feedstuffs.  There may also be more access to toxic plants.  With droughts come increased weed infestation of pastures, hay and crop fields.   Penned cattle may also be in corrals or drawn to low lying areas that are still green, both of which are where toxic plants are likely to grow.  Differentiating “good” vs. “bad” plants is a learned behavior, so toxicity is more likely in young animals and animals moved to a new location.  A grazing management and supplemental feeding plan is essential to minimize problems.  Veterinarians and producers should be familiar with which plants can cause problems in their area, and try to avoid them.  The following discussion covers some of the plants and situations to watch for during drought situations.  There may be plants that grow some regions that are not covered.

Stressed plants more readily accumulate nitrates and prussic acid (cyanide).  Drought stress can cause both pasture forages and weeds to accumulate toxic amounts of nitrates.  Recently fertilized pastures are also at higher risk.  Plants that have accumulated nitrates remain toxic after baling or ensiling.  Test forages for nitrates to prevent poisoning.  Prussic acid accumulates most often in sorghums, sudans and Johnsongrasses, but these plants can accumulate nitrates also.  There is no test for prussic acid, but it dissipates when plants are baled or ensiled, so harvested forages are safe.  Cattle poisoned by nitrates or prussic acid are usually found dead, so prevention of these toxicities is critical.   Cattle with nitrate toxicity have methemoglobinemia (brown blood) and cattle with prussic acid toxicity have cyanohemoglobinemia (bright, cherry red blood).  Nitrate and prussic acid both interfere with oxygen carrying capacity in the blood, so pregnant cattle surviving these poisonings often abort.

Two of the most toxic plants found in croplands and pastures are coffeeweed and sickle pod.  Cattle will generally not graze the green plant unless other forages are scarce.  However, they will readily eat the seedpods that are dry after a frost.  The plant remains toxic when harvested in hay/balage/silage.   Coffeeweed and sicklepod are toxic to muscles and cause weakness, diarrhea, dark urine, and inability to rise.  There is no specific treatment or antidote, and once animals are down, they rarely recover.

Pigweed or carelessweed is very common in areas where cattle congregate.  Cattle will readily eat the young plants, but avoid the older plants unless forced to eat them.  A common pigweed poisoning is when cattle are penned where pigweed is the predominant plant and no alternative hay or feed is provided.  Red root pigweed is more toxic than spiny root pigweed, but is less common.  Pigweed can accumulate nitrates, so sudden death is the most common outcome.  It also contains oxalates, so renal failure can also occur.

Black nightshade is common in croplands, and like pigweed, in often in high traffic areas.   The green fruit is most toxic, so cattle should not have access to nightshade during this stage, and nightshade remains toxic in harvested forages.  Nightshade is toxic to the nervous and gastrointestinal systems, and causes weakness, depression, diarrhea, and muscle trembling among other signs.  Bullnettle and horsenettle are in the same plant family as nightshade.  They are also toxic, although less so, and are usually avoided by livestock unless other forages are not available.

Blue-green algae blooms in ponds can also occur in hot weather.  They are most common in ponds with high organic matter, such as ponds where cattle are allowed to wade, or where fertilizer runoff occurs.  The blue-green algae accumulates along pond edges, especially in windy conditions, and exposes cattle when they drink.  Both the live and dead algae are toxic.  The toxins can affect the neurologic system causing convulsions and death, sometimes right next to the source.  They can also affect the liver, causing a delayed syndrome of weight loss, and photosensitization (skin peeling in sparsely haired or white haired areas).

Perilla mint causes acute bovine pulmonary edema and emphysema (ABPE), usually in late summer.  It grows in most of the central and eastern United States and is common in partial shade in sparsely wooded areas, and around barns and corrals.   There is no treatment, so prevention is critical.

Cattle with access to wooded areas may eat bracken fern.  Cattle must eat roughly their body weight over time before toxicity occurs, but may do this in situations where other forage is not available. Braken fern toxicosis causes aplastic anemia.  Fever, anemia, hematuria, and secondary infections are some of the most common signs.

As summer moves into fall, the potential for acorn toxicosis increases.  Cattle have to eat large amounts usually to become sick, but those that are in poor body condition and hungry are more likely to do so.  Clinical signs include constipation or dark, foul-smelling diarrhea, dark nasal discharge, depression, weakness and weight loss.

The lack of summer forages and the need for supplemental feeding during a drought can increase the likelihood of feeding “accidents” and toxicities.  Producers may be tempted to feed cattle pruning’s of ornamental plants, many of which are highly toxic.  Grain overload is also a potential problem if access to concentrate feeds are not controlled.  Salt toxicity can occur if hungry cattle are allowed free access to high salt containing “hotmixes”.  Even though these are meant to limit intake, initial intake can be high enough to cause toxicity in starved or salt deprived cattle.  Feeding byproduct feeds, candy, bread, screenings, etc. may also be more common, all of which have the potential to cause problems.  Producers may also be tempted to feed moldy hay or feed, which can lead to toxicity problems.

With careful planning, plant toxicities can be avoided. If you have questions on toxic plants and how to identify/avoid them, please contact your local veterinarian or Extension agent. If you have further questions please feel free to contact me at, lstrick5@utk.edu, or 865-974-3538.

Tall Fescue

With its drought, low soil pH, and high stocking density tolerance, tall fescue is the forage of choice in many pastures. While it may come off as a “super grass,” tall fescue can cause major health and reproductive issues in some animals.

Danielle Smarsh, equine extension specialist at Pennsylvania State University, addressed tall fescue toxicity in pregnant broodmares in a recent article published in Penn State’s Field Crop News.

“Certain varieties of tall fescue are infected with the fungus Neotyphodium coenophialum,” explains Smarsh. While this fungus is great for the plant since it protects against drought and some insects, it isn’t so great for grazing animals.

The fungus produces ergot alkaloids, which have harmful physiological effects in grazing animals, including pregnant broodmares.

Fescue toxicosis is a major risk if pregnant broodmares consume infected tall-fescue. Some of the many symptoms of fescue toxicosis include abortions, stillbirths, and weak foals.

Late-pregnancy broodmares are the only horses that have ill effects from grazing infected tall fescue. Research demonstrates that stallions grazing infected tall fescue show no signs of declining reproductive performance.

The exact amount of ergot on a given pasture varies depending on the time of year, the amount of fertilizer present, and plant variation.

The real kicker is that you can’t tell if tall fescue is infected or not just by looking at it; the grass has to be tested.

Take tall fescue samples in early summer and fall when grass is growing rapidly. The exact time to sample is highly dependent upon weather and region.

What can be done to mitigate the issue with pregnant broodmares?

If pastures test positive for endophyte-infected tall fescue, remove pregnant broodmares 60 to 90 days before foaling. Another option is to treat mares with domperidone to relieve most toxicosis symptoms. Consult with your veterinarian before taking this approach.

If enough space, time, and money is available, renovating pastures to remove the infected tall fescue is a possible option. Tall fescue can be removed with an herbicide and replaced with other cool-season grasses or endophyte-free tall fescue.

“This process can be costly and take several years, so it might not be the best solution for everyone,” Smarsh warns. She also notes that it is difficult to remove all infected tall fescue.

If a mix of cool-season grasses is used, identify the percentage of tall fescue in the stand. If the percent of tall fescue is small, there is less risk for broodmares to contract toxicosis. Even so, the best management option is to remove them 60 to 90 days before foaling.


To bloom or not to bloom?

By Kassidy Buse

A common recommendation of agronomists is to let one alfalfa cutting reach bloom each year.

Ev Thomas, retired agronomist from the Miner Research Institute in Chazy, N.Y., says otherwise in The William H Miner Agricultural Research Institute Farm Report.

“For many years, I’ve said that in managing alfalfa for dairy cows, you should never see an alfalfa blossom, from seeding to plowdown,” says Thomas.

Thomas also notes there’s room for difference of opinion due to no research supporting either opinion.

But, if one cutting is to bloom, which cutting should it be?

The first cut of alfalfa-grass typically contains the most grass. Grass, even the late-maturing species, is close to heading when alfalfa is in the late bud stage.

The second cut is exposed to long, hot June days that result in highly lignified, fine stems. A Miner Institute trial found that the stem quality of bud-stage second-cut alfalfa was no better than full-bloom first-cut alfalfa.

The third cut can be influenced by prior harvest management. If it was a late second cutting, the third cut was growing during midsummer heat. This cut would also have highly lignified stems.

The fourth cut often takes a long time to bloom, if it makes it there. A killing frost might arrive first.

For any cutting, the more grass in the stand, the lower the forage quality if alfalfa is left to bloom.

“The objective of letting alfalfa bloom is to improve root reserves, and therefore extend stand life,” says Thomas. “We need to balance the impact of delayed harvest on plant health with the economics of feeding alfalfa of lower quality that is needed by today’s high-producing dairy cows,” Thomas adds.

How alfalfa and alfalfa-grass is managed depends on if the goal in mind is long stand life or high milk production potential.

Protecting Your Animals This Summer

As it gets further into the summer months, livestock begin to show express a common discomfort as humans do: sunburn. Exposure to UV radiation can cause skin damage to dairy cows, light-colored beef cattle, sheep, pigs, and horses. Affected skin becomes red, painful and raised, which can lead to the skin becoming extremely dry and will eventually slough off leaving those areas exposed to secondary infections.

A cow losing patches of its coat due to sunburn
A cow losing patches of its coat due to sunburn

Sunburn not only makes the animal uncomfortable, it affects their overall productivity and performance. The body takes the nutrients that is needed for growth and uses them to repair the skin that is damaged. In dairy cows, this can lead to a decrease in milk production and in sheep, a decrease in wool quality. Sheep can be burned sheared or unsheared since the radiation is strong enough to penetrate through the wool. Pigs are one of the lucky animals that can protect itself form the suns rays. By wallowing in mud, the pig is forming a protective coating that shields the skin from the sun. Light coated animals are not as lucky. Cows and horses with predominantly white coats suffer more sunburn than those with dark coats. However, dark coats absorb more sun, which leads to more symptoms of heat stress.

UV radiation isn’t the only determinant of sunburn in animals. Animals that feed in wheat pastures with certain weeds are likely to develop photosensitivity. This is caused by a reaction within an animal’s body when the chlorophyll in some wheat plants release a toxin that increases sensitivity to the sun. Weeds such as barley, alsike clover, St. John’s Wort, nettles and others are some of the culprits in photosensitivity and can also be the causes of liver damage and neurological disorders that develop in the animal.

Preventing sunburn doesn’t just mean keeping them out of the sun, although providing a shady place for the animals can definitely help. If the sun is a concern, baby formula sunscreen can protect the areas that are more vulnerable to sunburn. Another way of decreasing sunburn is restricting the access of wheat pasture the animal is consuming to prevent photosensitivity. Adding grass hay in the morning when grazing intake is high helps in restraining the animal from consuming too much wheat during those times.

Nutrient Management Credits Offered at Upcoming Pasture Walks

The University of Delaware Cooperative Extension is offering pasture walks in two locations this spring.  Participants will have the opportunity to earn nutrient management and pesticide certification credits.  The first walk is being held on May 28th from 6:30-8:30 pm and is being hosted at the farm of Rick and Kim Vincent of Harrington and the second walk will be on June 4th from 6:30-9:00 pm at the University of Delaware’s Webb Farm in Newark.  Program agendas are listed below.  Participants are welcome to bring a plant or weed sample with them for identification.  Please pre register if you plan on attending either program.

Past Participants with Forage Sticks
Past Participants with Forage Sticks

May 28th Pasture Walk Hosted by Rick and Kim Vincent

3427 Burnite Mill Rd. Harrington, DE 19952

6:30-8:30 pm

Welcome and Introductions– UD Cooperative Extension Staff

Farm Overview/Current Pasture/Grazing Management– Rick and Him Vincent, Hosts

Pasture Plant Species ID– Dr. Richard Taylor, Extension Agronomist

Soil Fertility and Pasture Health– Dr. Richard Taylor, Extension Agronomist

Weed ID and Weed Control in Pastures– Quintin Johnson, Extension Agent Weed Science

Soil Sampling Techniques, Sample Submission and Testing Options– Bill Rohrer, Owner and Manager AgroLab

DE NM Credits 1.25   Pesticide TBA

To register for this pasture walk, please call (302)730-4000 or email truehart@udel.edu by May 27th


June 4th Pasture Walk Hosted at the University of Delaware Webb Farm

508 S. Chapel Street Newark, DE 19716

6:30-9:00 pm

Tour of Pastures and Management, Pasture Renovation Techniques – Larry Armstrong, UD Webb Farm Manager

Soil Fertility, Plant ID, Bermudagrass Establishment – Dr. Richard Taylor, Extension Agronomy Specialist

Weed ID and Weed Control in Pastures – Quintin Johnson, Extension Agent, Weed Science

Soil Sampling techniques and Proper Sample Submission- Karen Gartley, UD Plant and Soil Science Research Manage

Overview of NRCS Programs- Marianne Hardesty, New Castle County NRCS District Conservationist

DE NM Credits 1.75 Pesticide TBA

            To register for this pasture walk or  request more information, please call (302)831-2507 or email severson@udel.edu by May 30th