Poison plants threaten livestock in dry pastures

Livestock normally avoid toxic plants since they tend to taste bitter, like this spotted water hemlock, much as they avoid water that is too high in sulfates. In the middle of a drought, though, producers need to take measures to ensure their livestock don’t give in to temptation. | USDA photo

Livestock are tempted to nibble on anything green as pastures dry down and grasses stop producing, but foraging on these plants can have deadly consequences.

“Certainly it’s prudent to manage and monitor your cattle all the time, especially this August-September time period,” said Bart Lardner, a professor in beef cattle management at the University of Saskatchewan.

Livestock normally avoid toxic plants since they tend to taste bitter, much as they avoid water that is too high in sulfates. In the middle of a drought, though, producers need to take measures to ensure their stock don’t give in to temptation.

Lardner counsels things like fencing around streams, lakes and sloughs and solar pump systems to move the water upland to a trough.

There are some nasty customers lurking among the cattails and wild onions. Water hemlock, for example, is one of the most toxic plants in North America.

Clark Brenzil, provincial weed specialist for Saskatchewan, writes in a recent blog that the plant is shallow-rooted, making it easy for cattle to inadvertently pull from the ground, root and all, while grazing. These bulb-shaped roots are filled with a highly poisonous fluid.

“Should an animal get hold of and consume one of these bulbs, death is quick and painful, as the amber liquid is an acute nerve toxin,” he writes. Symptoms include violent seizures.

Fortunately, water hemlock plants can be easily dug out with a shovel and removed, although care should be taken to use gloves when handling. For larger stands, herbicides such as MCPA are registered for control as well.

Another potentially harmful plant to watch for is seaside arrowgrass, which is not a true grass at all, Lardner said.

Seaside arrowgrass. | USDA photo

“It’s a grass-like perennial herb common in alkali areas where you see sedges and rushes growing.”

Seaside arrowgrass contains cyanogenic glycosides. These are the same type of chemicals found in wild almonds and responsible for their bitter taste. They are also present in chokecherries, pincherries and sandcherries, whose leaves cattle can be tempted to eat when other forage is unavailable.

Once eaten, cyanogenic glycosides are broken down in the digestive system to produce toxic hydrogen cyanide. While a little can be tolerated — bitter almonds are used in some countries for cooking — too much can be harmful. Cattle that have had too much display rapid and laboured breathing, bluish tissues around the mouth, increased salivation, and, in the worst cases, convulsions and death.

A related group of chemicals are found in showy milkweed, another troublesome plant. These are called cardiac glycosides, and as their name implies, they cause speeding or slowing of the heart, leading to stroke or heart failure.

Showy milkweed. | USDA photo

One of the more attractive of the treacherous pasture plants are the two-grooved milk vetch and narrow-leaved milk vetch. Some species boast plentiful purple flowers, although their scent has been described as reminiscent of dirty socks thanks to their high levels of selenium compounds. While selenium is needed as a micronutrient, a little goes a long way.

Two grooved milkvetch. | USDA photo

“The requirement is very low, point one parts per million,” Lardner said. “With these two-grooved milk vetch, they can absorb up to 8,000 parts per million of selenium, so all of a sudden you’ve got a toxicity issue waiting for that animal when it does seek out those greener plants in those wetter, boggy alkali slough areas.”

Narrow leaved milkvetch. | USDA photo

Vetches can also be found in the uplands where they are often the only green plants amid dry, dormant grasses.

Producers looking for a definitive source on these and other threats to their herds, could refer to the book, Stock-poisoning Plants of Western Canada. It is available for free from several sources online, including the Beef Cattle Research Council at www.beefresearch.ca.

Lardner recently took part in a July 29 webinar called Experiencing Drought Stress? Ask the Experts.

The BCRC webinar drew more than 300 participants and is available on the BCRC YouTube channel.

“I think the big thing that I’ve been hearing is that there are a lot of cash crops that have been seeded and so I think we’re in the salvage area right now of all types of different crops,” he said. “Not just the issue of trying to manage for toxic plants and anti-quality factors.”

Typical questions during the webinar included whether drought-damaged canola or flax can be used as forage, whether malting barley can be used, and whether herds can be turned out onto lentil crops to graze. Generally, the answers were positive, but with stipulations that, for example, salvage crops make up no more than one-third of cattle rations.

“The other thing I’m finding is that water quality is going downhill fast,” Lardner said. Evaporation is concentrating dissolved materials, such as sulfates and phosphorus compounds, the latter of which can cause blue-green algae blooms.

“Water quality is a big issue, right alongside toxic plants,” Lardner said.

He urged producers to seek information. Get water and feed tested, and consult the experts for help.

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