List of Cover Crop Plants You Should Know That Are Toxic to Cattle

by Caitlyn Andrews April 29, 2016

List of Forage Cover Crops that are Toxic to Cattle

Are you aware of the dangers potentially growing in your cattle's grazing pasture? If you're considering planting a cover crop for forage, or unaware of which plants can be toxic to cattle, then this article is for you.

Plants Poisonous to Cattle

Just recently the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, or K-State Research and Extension for short, released a publication that details which cover crops are poisonous to cattle. The publication also provides information on which plants can potentially cause metabolic disorders.

A driving force for releasing the publication is the idea that some producers could be feeding their cattle toxic plants without even knowing it. Producers need to be aware of which plants could harm their cattle and other livestock. This publication seeks to arm producers with this vital information.

K-State Grazing Management: Toxic Plants Summary

For the full publication click here. Here is a summarized list of the toxic plants to cattle discussed in detail in the publication:

Poisonous Plants

  1. Hairy Vetch is a nitrogen-fixing plant that works well as a cover crop. However, it is not recommended for livestock because of its toxicity to cattle and horses. The mortality rate for affected animals ranges from 50-100%, typically as a result of kidney failure. Any stage of hairy vetch growth is risky for grazing. Animals with black pigmented skin (Angus and Angus crosses, Holsteins and black horses) are the most susceptible. Hereford cattle can also be affected. Hairy vetch poisoning is linked to herd genetics, but there is no genetic test to indicate livestock sensitivity.
  2. Lupin is a good source of protein and energy for both ruminants and monogastrics, but only when the 4 nontoxic species are used: narrowflower lupine, white lupine, European yellow lupine, and tarwi. There are 6 toxic lupin species that are particularly toxic to cattle and sheep: silky lupine, tailcup lupine, velvet lupine, silvery lupine, summer lupine and sulfur lupine. These poisonous varieties can kill sheep and cause serious birth defects when consumed by pregnant cows such as cleft palates, crooked legs, and distorted or malformed spines.
  3. Amaranth is used for grain production. The species used include love-lies-bleeding, red amaranth, and Prince-of-Wales feather. Spiny amaranth, also known as spiny pigweed, redroot pigweed, and Palmer amaranth are all classified as true weeds and hard to control in pastures. Palmer amaranth is high in nitrate and potentially toxic to cattle. Know which species of amaranth you have before allowing cattle to graze.
Plants Toxic to Cattle Hairy Vetch
Pictured Above: Hairy Vetch

Image source: Wikipedia

Metabolic Disorders Caused by Plants

  1. Bloat is the condition that occurs when a ruminant consumes feeds that produce thick, foamy gas that the animal cannot pass. Froth builds in the rumen and causes discomfort. The condition can be fatal if pressure isn't alleviated. Bloat prevention agents such as ionophores and poloxalene can be added to feed and water to reduce risk. Products such as Bloat Release can help alleviate the condition as well. Grazing a grass-legume mixture is recommended, but producers should avoid pastures that contain more than 50% bloat causing legumes. We'll discuss these legumes below.
  2. Glucosinolates are natural compounds that give plants a bitter taste. They can interfere with thyroid function, cause liver and kidney lesions, and reduce mineral uptake. Inhibited iodine uptake can result in goiters.
  3. Grass Tetany, aka grass staggers or wheat pasture poisoning, is characterized by low magnesium levels in the blood. It primarily affects older, lactating cows grazing on succulent, immature grass. It causes staggers, convulsion, coma and even death. Prevent grass tetany by supplementing magnesium and grazing high-risk pastures with steers, heifers and dry cows instead of older, lactating cows.
  4. Nitrate Toxicity occurs when plant nitrate is converted to nitrite in the rumen. Symptoms include staggering gait, rapid pulse, labored breathing, frequent urination, collapse, abortion in pregnant cows, coma and/or death.
  5. Polioencephalomalacia (PEM) occurs when high levels of dietary sulfur create hydrogen sulfide gas in the rumen. This can lead to brain lesions and PEM. Signs include muscle incoordination, circling, stupor, blindness, facial tremors, recumbency, convulsions, and death. Treatment may include intravenous thiamine injections and dexamethasone. 
  6. Prussic Acid Poisoning can occur rapidly on high-risk forages and can result in sudden death. Symptoms include staggering, gasping, trembling muscles, convulsions and respiratory failure. Mucous membranes in the mouth and eyes may turn blue. It can also be diagnosed by cherry red blood at death. Treatment of sodium nitrite and sodium thiosulfate should be administered intravenously by a vet. Avoid grazing on forage with new growth that produces high levels of prussic acid or after a light freeze.
  7. Sweetclover Poisoning can be associated with coumarin, a substance that's converted to dicoumarin in spoiled or damaged sweet clover. It interferes with vitamin K metabolism and blood clotting and can result in hemorrhaging. Reduce your cattle's risk of sweet clover poisoning by not feeding moldy sweet clover hay and planting low-coumarin clover varieties. Treatment includes intravenous injections of vitamin K or whole blood.

Additional Crops That Cause Metabolic Disorders

  1. Brassicas (Kale, Rapeseed, Swede, Turnip, Canola and Mustard). Maladies associated with brassica grazing include polioencephalomalacia, hemolytic anemia, pulmonary emphysema, nitrate poisoning, bloat, and metabolic issues associated with glucosinolates. Nitrate toxicity is also possible with brassicas. Canola increases the risk of PEM.
  2. Flax. Grazing flax is not recommended because of its potential to cause prussic acid poisoning. Avoid grazing flax straw. Harvested flax seed can make a good high-protein feed, though.
  3. Small Grains (Barley, Oats, Rye, Ryegrass, Wheat, Triticale). Rapid growing, lush grasses can lead to grass tetany when grazing cattle. High-protein grasses may contribute to bloat. Nitrate toxicity risk increases with heavy nitrogen fertilization of cool-season grasses.
  4. Legumes. Grazing cattle on sweet clover, yellow clover, and white clover puts them at risk for sweet clover poisoning. Avoid feeding moldy sweet clover hay to cows within 2 weeks of calving to reduce the risk of abortion. Bloat is another concern with grazing legumes and clover. Annual lespedeza, birdsfoot trefoil, medics, and sainfoin can cause bloat. Some birdsfoot trefoil species may also contain high levels of prussic acid.
  5. Sorghum, Sudans, Millets and Corn. Four main categories of sorghum and millets are grain sorghum, forage sorghum, sudangrass and sorghum-sudan-grass hybrids. These all put grazing cattle at risk for prussic acid HCN poisoning. Curing removes prussic acid from sorghum hay but leaves nitrates as a risk to cattle. Nitrate toxicity can be a problem with grazing pearl or foxtail millet. Corn and sorghums have also been associated with nitrate toxicity. Test forage before grazing or using for hay.

Caitlyn Andrews
Caitlyn Andrews


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