K-State Research and Extension

Farmers use cover crops to reap plenty of benefits. Cover crops are a great way to slow down erosion or to stop weeds from covering fields. They can attract pollinators. Some varieties take nitrogen from the air and store it in their roots to benefit soil quality. And for livestock producers, cover crops have an added benefit: they also can serve as forage for grazing animals.

However, the reality takes more planning to avoid losses for farmers – some of them catastrophic.

Cover crops are a little bit like the story of Goldilocks: there are only some considered “just right” for cattle and deemed “very safe” by experts. Other varieties are “too hot or too cold”: they can cause metabolic issues for livestock that, while manageable, can be an unpleasant surprise for uninformed producers. Still other cover crop varieties are so toxic, they can kill entire herds.

Jaymelynn Farney, a beef-systems specialist and assistant professor in the Department of Animal Sciences and Industry at K-State, is an expert on cover crops as forage. Her work explains which cover crops make good forage for livestock, describing how producers can manage the common metabolic disorders for cattle on cover crops, and warning farmers away from the most toxic species.

Farney is a co-author of a comprehensive K-State Research and Extension publication about forage crop characteristics and toxicities. In it, 56 types of forage crops are listed. Out of this number, nearly three-quarters of them caused some sort of metabolic disorders in cattle, sheep and horses. Common metabolic disorders include: bloat, grass tetany, nitrate toxicity, prussic acid poisoning, sweetclover poisoning, polioencephalomalacia (PEM), and glucosinolate poisoning.

The toxic potential of some cover crops makes Farney “nervous,” but she remains confident that, by making more information available to producers, they can make informed decisions that will benefit their operations.

In a recent article for Progressive Cattleman, Farney categorizes cover crops as “poisonous” or “manageable.” Most importantly, she warns producers away from the most toxic of the lot: hairy vetch, as well as varieties of amaranth and lupin.

“[Hairy vetch] is an indiscriminate killer,” Farney said. She worries when she sees this crop growing as forage because, while many producers use it without issue, some animals actually have an allergy to the plant which leads to death in 50 to 100 percent of affected livestock.

Farney admits that there’s no way to test for this reaction: researchers don’t know what part of the plant makes animals react this way, so they cannot tell when hairy vetch is safe for grazing, or what part of the plant is safe. Nor can they test to discover which animals might have a reaction to hairy vetch, so using this cover crop as forage is a game of chance: producers might have a healthy, robust herd, or a dead one. It’s the difference between a vigorous herd and a decimated one.

“While we don’t see a lot of cattle affected by [hairy vetch], but when you do, it can be devastating,” said Farney.

She adds that five species of lupin are very toxic, causing birth defects like cleft palates, crooked legs, or malformed spines. Farmers should avoid planting silky, tailcup, velvet, silvery, or silver lupine varieties where cattle are grazing. The same is true of amaranth, which has three toxic varieties: spiny amaranth, redroot pigweed and Palmer amaranth. Farney says that this plant also causes additional problems because it is a “true weed” and is glyphosate resistant.

Although producers need to use a healthy dose of caution when planting cover crops as forage, there are many varieties that will benefit both field and farm. Small grains, legumes, sorghums, millets, corns and flax are all cover crops used as forage. All of them have issues that producers can offset, with proper management.

Farney believes that cover crops are a worthwhile investment for producers, because known management practices can offset any metabolic issues. The most important steps to take when thinking about using a cover crop as forage? Plan ahead, said Farney.

“Determine the goals for [your] operation,” she advised, because these goals can determine the choice of plant species or management decisions. Cover crops can be a valuable asset to any operation, and, with the proper planning and prioritizing, these forage opportunities won’t be a roll of the dice.