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Poisonous Plants and Livestock

By Jenifer Heyden MSc. PAg., Livestock and Feed Extension Specialist, North Battleford

May 2024

Each year, livestock producers lose animals to encounters with poisonous plants. Recognizing problem plants and understanding management opportunities to reduce the risk of poisoning are important tools in preventing a serious problem. Be aware of plants that may cause issues, familiarize yourself with identifying these plants and learn some of the symptoms that correspond with the ingestion of poisonous plants.

Poisonous plants contain toxic substances that cause harm. The amount of toxin in a plant can vary with stage of growth or may be more concentrated in certain parts of the plant such as the leaves or seeds. Some plants have spines or prickles that cause physical injury. Others contain substances that can cause skin blisters, abortions, birth defects or weight loss. Different species of livestock have different reactions and sensitivity to poisonous plants; age of the animal can also influence the reaction and susceptibility. Depending on the type of toxin and amount eaten, an animal's reaction can range from reduced performance to death. Some plants cause sickness or death within a very short timeframe, while others may take several days or weeks.

Under certain circumstances the ingestion of poisonous plants is more likely to occur:

  • When livestock are being moved to a new location, they are less particular about what they’re eating and more worried about eating something. Often, poor choices are made.
  • Young animals are curious and will often eat plants that older animals would not.
  • Some older animals are repeat offenders and despite digestive upset or other afflictions, these animals will continue to consume toxic plants.
  • Overgrazing causes good forages to be reduced in number and weeds and poisonous plants can become more abundant.
  • Limited moisture and dry conditions reduce the amount of forage that is available and livestock eat whatever exists.
  • Drought ridden hay fields are often laced with weeds and poisonous plants that end up being baled along with hay.

Some of the toxic plants in Saskatchewan include water hemlock, seaside arrow grass, locoweed, lambs quarters, horsetail, larkspur, saskatoon, and chokecherry among others. Water hemlock is considered to be the most toxic poisonous plant. Identifying these plants in grazing situations is key to preventing harm to your livestock.

Sorghum plant
Sorghum/sorghum-sudangrass hybrids may
accumulate prussic acid under certain conditions;
prussic acid can be toxic to livestock.

What about forages that we have seeded; can these be toxic? Polycrops contain two or more plant species that may include warm season forages, cool season forages, legumes or brassicas. Some of these plant species can contain antinutritional factors. Sulphur, found in brassica species like kale, turnip, radishes or canola can bind to trace minerals like copper, causing trace mineral deficiencies. In high enough amounts, sulphur itself can be toxic, causing blindness or polio. Elevated nitrates, resulting from stress events, can be present in spring cereals or warm season grasses. Potassium can accumulate in many species that are commonly used in polycrop blends. Flax and sorghum/sorghum-sudangrass hybrids may harbour prussic acid under certain conditions leading to asphyxiation. Despite potential issues, these blends are highly nutritious and can offer reprieve to tired pastures during the grazing season if managed correctly.

Management is key, regardless of whether we are talking about pasture, hay or a polycrop used for grazing. On pasture, scarcity of palatable forage, lack of water or lack of salt may cause animals to graze greenery that might otherwise be rejected. Consider forage and water testing, follow good grazing management principles – don’t turn livestock out hungry onto a new paddock, limit intake if possible, allow access to other roughages or dry feed and be aware of selective/preferential grazing. Steps can be taken to avoid livestock plant poisoning. Know what’s in your pasture, hay or your polycrop blend. Be aware of the dangers and be ready to take action if necessary.

A recent webinar, covered much of the content here in greater detail. For more information about managing poisonous plants, or other livestock related topics, contact your local livestock and feed extension specialist or the Agriculture Knowledge Centre at 1-866-457-2377.

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