With the last several years of drought in Montana, livestock producers may want to be especially mindful of watching out for the effects of several weed species that can be toxic to livestock.
During winter feeding, recognizing that hay being fed or pastures being grazed during the winter months can have high loads of plant toxins can prevent livestock illness and death, according to Jennifer Solf, an Extension agent with Montana State University (MSU).
“There are two kinds of plant toxins that can negatively affect livestock – nitrates and oxalates,” Solf explained during a presentation at the MATE show in Billings, Mont. “Nitrates turn into ammonia in the blood and create difficulty breathing, staggering, and potentially death. Oxalates have high quantities of potassium and salts that can’t be metabolized by the rumen and can cause kidney failure.”
Nitrates are found in weeds like redroot pigweed, kochia, curly dock, lambsquarter and nightshade. Oxalates are found in plants like purslane, common mallow, redroot pigweed and lambsquarter.
Knowing the detrimental effects these plants can have on livestock, producers can take several steps to avoid having their animals poisoned by them.
Grazing and weed identification
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With spring grazing just around the corner, many pastures may have higher concentrations of weeds than normal due to the previous drought conditions.
“During winter feeding, hay from new sources or out-of-area sources may have been depositing weed seeds that will come up in the spring,” she said. “If the grass in that area is grazed lower than two inches, it can give dormant weed seeds a chance to sprout and multiply.”
Being aware of weed presence, type, and density is important as some weeds are only toxic at certain levels.
“Knowing what cattle or sheep may prefer to eat and a weed’s palatability in the growing cycle is important,” Solf noted. “Most grazers like to eat toxic plants when they are in the early growth stage, which is unfortunately when they have the most toxins. Some weeds, like poison hemlock, only have to be consumed in small amounts and the negative effects can be seen within the hour. Other plants, like lupin, don’t have an immediate impact but can negatively affect pregnant cows.”
Identifying what kinds of weeds are present in a grazing area is a matter of both visual identification and testing. Testing is offered through several labs, including MSU Extension, who will test the plants for free.
“It’s helpful to note that cattle are more interested in grass, while sheep and goats are more interested in forbs and shrubs, but if there is not enough good forage in an area, both will be forced to eat plants that can be toxic,” Solf related.
Because some pastures may have a high concentrations of plants that are toxic, Solf said avoiding certain pastures until the weeds are under control is important.
“The best thing you can do this coming season is to identify the plants in your area so you can control them. Plan your grazing so livestock don’t have them as a forage option,” she said. “In the meantime, pray for rain.”