Why do animals eat toxic plants?
Animals usually leave bad-tasting plants alone when there is enough to eat. Trouble comes when pasture is short, after frost or drought changes how plants grow, when new animals do not know the local plants, or when hay contains weeds that were baled with the crop. Cuttings of some plants stay toxic when dried, and animals cannot sort them out of a flake of hay.
That is why extension guidance from several states focuses on keeping pasture dense, managing grazing height and checking hay, not only on identifying weeds.
Different species differ in what they eat and how much they browse, so ask your extension office which plants matter most for sheep, goats, cattle, horses, pigs or poultry in your area. A plant that is a concern for one species may be less of one for another.
How do you find out what is growing on your land?
Walk each field in spring and again in late summer and photograph every plant you cannot name. Take clear pictures of leaves, flowers and the whole plant. Your county extension office can identify samples and often has a regional list of plants of concern in your area. Do not guess from a book alone, because many plants look alike.
Use an expert for identification and never taste or handle unknown plants to test them. Wear gloves when pulling suspect weeds, since some irritate skin.
- Photograph whole plants, leaves and flowers
- Note where each patch is on a field map
- Check fence lines, ditches and wooded edges
- Ask extension to confirm before you act
What conditions raise the risk?
Risk climbs when pasture is overgrazed and weeds fill bare spots, when animals are turned out hungry onto a new field, and when yard waste, clippings or ornamental plants are within reach over the fence. Garden trimmings thrown over a fence are a quiet cause of problems. Wilted leaves after storms or frost can also change how a plant behaves.
Feed animals before turning them onto weedy or unfamiliar ground, and move them off short grass sooner.
Also watch for plants that grow back after mowing or tilling, and for plants that appear after soil is disturbed, such as around new construction, ditches or where you have spread fill. New ground often brings new weeds.
What are the warning signs of poisoning?
Signs vary by plant and species, and many look like other illnesses. Possible signs include sudden depression, drooling, staggering, tremors, bloating, trouble breathing, collapse, diarrhea, or sudden death in an animal that looked fine the day before. You cannot tell the cause from signs alone.
Poisoning is an emergency. Call your veterinarian right away, describe what you see, and tell them what the animal may have eaten and where. Move other animals off the suspect pasture or feed while you wait, and keep a sample of the suspect plant in a bag for identification. Do not try home remedies or give anything by mouth unless your vet tells you to.
If more than one animal is affected, or if animals die suddenly, tell your vet that right away. The pattern helps them decide what to check, and it may help you find the source in time to protect the rest of the herd.
How do you reduce the chance of a problem?
Keep pasture thick and healthy so weeds have less room. Control problem plants using methods suggested by your extension office. If herbicides are involved, follow the label exactly, since the label is the law, and ask whether grazing restrictions apply after treatment, because some treated plants become more attractive to animals.
Inspect hay when it comes in. Open a few bales, look for weeds, mold and odd smells, and ask the seller what was in the field. Keep fences tight against neighboring brush and ornamental plantings, and never dump trimmings where animals can reach.
Keep records of where and when you saw problem plants, what you did and what happened. These notes help you the next year and help your vet or extension agent if a problem arises.
Who should you contact?
Save the numbers for your veterinarian, the nearest large-animal clinic, and your county extension office in your phone before you need them. Some states have animal poison resources or diagnostic labs, and your vet will know which to use.
Rules about reporting unexplained livestock deaths vary by state, so ask your state veterinarian or extension office what applies to you.
Key takeaways
- Know what grows in every field and have unknown plants identified by an expert.
- Hunger, drought and weedy hay raise risk.
- Poisoning is an emergency: call your vet right away.
- Never dump yard trimmings where animals can reach them.
- Herbicide use follows the label and any grazing restrictions.
Sources and further reading
Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.