Prairie Post (West Edition)

Toxic Plants and other toxin risks


Toxic or poisonous plants are more likely to be grazed during dry years as forage sources become depleted and grazing animals search for plants to graze. Hungry animals become less selective in what they eat. To prevent animals from grazing these plants, it is important to monitor pastures or provide supplement­al feed to ensure that animals are not lacking forage and choosing species that may be dangerous.

Some plants produce a toxin themselves, while in others the toxin is produced by microorgan­isms growing on or inside the plant4.

Just a few examples of the numerous plants that can cause poisoning to livestock include:

native species such as: chokecherr­y tall larkspur; as well as introduced weeds including common tansy and locoweed.

An in-depth overview of plants that most frequently cause poisoning and injury to livestock in Western Canada is provided in the publicatio­n, Stock-poisoning Plants of Western Canada.

Stressed plants are more prone to accumulate high levels of toxic compounds such as nitrates or prussic acid. Under drought conditions, plants reduce or stop growth which can cause plant nitrates to accumulate to an unsafe level. Nitrate levels greater than approximat­ely 0.5% Nitrate (NO3) can be dangerous for animals. Annuals such as barley, oat, wheat, corn, and canola tend to accumulate greater amounts of nitrates than perennial forages while legumes do not generally accumulate nitrates. Prussic acid toxicity is caused by hydrogen cyanide (HCN) production in some plants including some varieties of birdsfoot trefoil, flax, sorghum-sudan grass, millets and chokecherr­y. Drought-stunted plants accumulate hydrogen cyanide and can possess toxic levels at maturity.

Water Sources

Sources of water for grazing animals can quickly become limited or unavailabl­e during drought periods. From a proactive management perspectiv­e, it is recommende­d that any pastures that could possibly run out of water be grazed first. In some cases, and where possible, it may become necessary to use a portable stockwater supply in order to continue grazing a forage source where water has become limiting.

Fencing off water sources and pumping to a remote site, such as troughs, will improve water quality and reduce water losses that occur when livestock have access to non-fenced sources. More informatio­n on the use of water systems is available in the BCRC Blog, How Quickly Do Water Systems Pay for Themselves?

Water quality is an extremely important aspect of livestock management and is more likely to become compromise­d during periods of drought. Concentrat­ions of total dissolved solids, sulphates and nitrates in both well and surface water may increase, mainly due to increased evaporatio­n and decreased rainfall to recharge sources5. Because increased concentrat­ions of minerals and contaminan­ts can negatively affect grazing performanc­e and potentiall­y lead to death at high enough levels, water testing is recommende­d. Producers must also be aware of the risks of cyanotoxin­s produced by blue-green algae (algal blooms) on standing water during hot summer months, which can cause sudden death when ingested. Treatment of the water source or limiting access to algae-affected standing water sources is often the best solution, when possible.

The BCRC webinar, What’s in your Water? Water Quality and Economics of Pump Systems, is an excellent resource providing details on testing water and preventing animal health issues

 ?? Photo credit Don Graham, Wikimedia ?? Chokecherr­y bushes are toxic plants for livestock.
Photo credit Don Graham, Wikimedia Chokecherr­y bushes are toxic plants for livestock.

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