Children are taught from an early age to steer clear of bottles marked with a skull and crossbones, understanding that this symbol means poison. If only teaching livestock to stay away from dangerous substances were that easy! That’s why it’s your job to safeguard your livestock from poisons commonly found on the farm.

“The toxins that large animals get into are different than small animals due to their housing situations,” says Tina Wismer, DVM, DABVT, DABT, medical director at the American Society for the Prevention of Cruelty to Animal’s Animal Poison Control Center. “While dogs and cats are most commonly exposed to human medications, large animals are more likely to be exposed to toxic plants, insecticides and herbicides.”

Take a look at seven substances that could be putting your livestock at risk and what you can do to keep them away from nibbling mouths.

1. Toxic Plants

Poisonous plants are possibly the toughest to control, as they can be found in pastures and in hay. The plants that are poisonous for one species may not affect others, and toxic species that are prevalent in one region might be unheard of in another. Understand what plants can be dangerous to your animals, and get to know the species that grow in your area.

“Walking the pasture with a county extension agent can help you identify any plants that could be potentially dangerous,” Dr. Wismer suggests. “Hay should always be examined before using and discarded if it is very weedy.”

Poisonous plants in the pasture can be especially troublesome during periods of drought and overgrazing. Weeds tend to thrive while forages suffer, and livestock could turn their attention to the toxic plants instead of  the grasses and forbs they typically graze. Well-meaning neighbors and visitors can also cause trouble on the feeding-toxic-plants front: “Never throw tree or shrub trimmings over the fence to livestock without making sure what type of plant it is,” Dr. Wismer cautions. Classic examples of accidental poisoning include yew trimmings given to cattle and red maple fed to horses.

2. Insecticides

Controlling pests is an important job on the farm, and finding ways to do so without chemicals is good for you, your land and your livestock. Consider integrated-pest-management techniques—including floating crop covers, beneficial insects and insect traps—to control crop pests. Look into herbal fly sprays, beneficial insects and insect traps to reduce insect populations around livestock, and keep your farm and home well-maintained to reduce insects’ interest in your property. When you do turn to chemical pest control, read and follow label instructions appropriately.

“Do not use a product on an animal that it is not labeled for, such as a cattle product on a horse,” Dr. Wismer says.

Storage conditions are paramount to preventing chemical poisoning, as well.

“Many problems can be avoided by making sure fences and gates are secure,” Dr. Wismer continues. “Fertilizers, insecticides and herbicides should all be kept in labeled containers behind locked doors.”

3. Herbicides

Often used to kill poisonous plants, chemical herbicides can also poison livestock.

“Herbicides may also make poisonous plants taste better before they die,” Dr. Wismer says. “Always follow the grazing restrictions on the label or contact the manufacturer about grazing restrictions before you use the product.”

In place of chemical herbicides, control weeds with rotational grazing to keep pastures healthy; an effective crop-field weeding schedule; cover crops on fallow fields; stale crop-seedbed preparation; and weed barriers, such as landscape fabric and mulch, in crop rows. Stay on top of your weed-control strategy so weeds cannot go to seed and repopulate themselves. If you use manure as a fertilizer, be sure it’s well-composted first to kill any weed seeds present.

4. Lead

Banished from paint in 1978, this harmful material is still used to manufacture batteries, ammunition and metal products. It’s also a naturally occurring element. According to the U.S. Environmental Protection Agency website, “Natural levels of lead in soil range between 50 parts per million and 400 ppm. Mining, smelting and refining activities have resulted in substantial increases in lead levels in the environment, especially near mining and smelting sites.”  Livestock can ingest soil-based lead both by eating plants that have absorbed the lead and by directly ingesting the contaminated soil. If you live in an area with high lead concentrations, have your well and soil tested.

“Lead poisoning still occurs in large animals. It can be from automotive batteries being left in pastures or animals licking peeling lead-based paint,” Dr. Wismer says. “Never leave junk piles in the pasture, and make sure the paint on your barn or fences does not contain lead.”

According to the Merck Veterinary Manual website, blood lead levels of .35 ppm and liver or kidney cortex lead levels of 10 ppm causes lead poisoning.

5. Moldy Hay

Not only do moldy forages have less nutritional value than high-quality forages, the molds can create mycotoxins that are toxic to animals. Mycotoxin toxicity in livestock can cause a range of problems, from decreased weight gain to abortion to death. Horses, in particular, are susceptible to colic from moldy feeds.

Inspect your hay and silage for mold before feeding it. Mold is generally easy to spot, smell or feel. (It creates heat in the bale.) Any bales or sections of bales that look off should be thrown to the compost pile rather than fed to livestock. Proper hay harvesting and storage under dry conditions are essential to preventing mold formation in cut forage.

6. Drought- and Frost-stressed Plants

Prussic acid and nitrate are two forage-toxicity concerns in drought, particularly for ruminants but also for horses. According to the North Dakota State University Cooperative Extension, plants may have higher levels of prussic acid during drought because the immature forage grasses contain mostly leaves, which produce two to 25 times more prussic acid than stems. Also, plants’ prussic acid content is higher in soils with high nitrogen and low phosphorus levels and in plants where chemical herbicides are used. Forages that might carry a higher risk of prussic acid toxicity include Johnson grass, birdsfoot trefoil, sudangrass and hybrids, sorghum and hybrids, flax, white clover, and Indian grass.

The NDSU Cooperative Extension also states that high levels of nitrate can be found in whole-plant corn silage, oats, corn, barley, pearl millet, sorghum, sundangrass and sorghum-sudangrass crosses, especially those that have been heavily fertilized with high-nitrogen/low-phosphorus and -potassium fertilizers. Pigweed and lamb’s quarter are two common weeds that might also accumulate nitrate. In the case of nitrate, stalks and stems pose the most risk.

You can have your forages tested for these toxins before allowing grazing or before harvesting for feeding and storage.

7. Vermin Poisons

“Many horses are exposed to rat and mouse baits every year because they are able to get out of their stalls, [and] rat/mouse baits are grain based and very tasty to horses,” Dr.  Wismer says.

Better than setting out chemical poisons for rats and mice on the farm, hire a couple of dogs and cats, use live traps, or use nonchemical rat repellents.  Also keep your feeding and food-processing areas clean to give vermin less incentive to visit.