How quickly things can change here in Ohio! Not much longer than a month ago, while I was moving cattle from one paddock to another, I was amazed at how wet it was for the middle of July. It seemed more like early March weather because it was really muddy when I put the cows through a gate into a new paddock. I don't ever remember my livestock pugging paddocks in July before, but there was some this year.
Now as we near the end of August I see a lot of water tanks on trucks hauling water for livestock to drink and many pasture fields are brown from forage plants going dormant due to lack of moisture. Rotationally grazed paddocks appear less affected than continuously grazed areas, but forage regrowth has really slowed down leaving some producers short on pasture for their livestock to graze.
Poisonous weeds that are in pastures and not appealing to livestock before may now become the forage that is left and sometimes eaten. There are also weeds, normally non-toxic to livestock, which build up nitrates when stressed and can cause death. A perennial grass such as johnsongrass and weeds like pigweed, mustard, nightshade and lamb's quarters can accumulate dangerous levels of nitrogen along with stinging nettle, elderberry, burdock and Canadian thistle to name a few. If you haven't observed your pastures much lately, now would be a good time to take a walk and see what is growing in your fields.
During drought type conditions cases of poisoned livestock are usually documented and more suspected. Included here are some plants to be aware of if they are in your livestock's forage.
Poison hemlock - All parts of this plant are poisonous, though roots are more toxic than leaves or stems. Leaves are especially poisonous in the spring, whereas the root becomes more toxic over time.
Groundsels, Ragwort - All parts of common groundsel contain toxins; however, toxin concentrations are greatest in the flowers, and in the leaves just before flowers reach maturity.
Milkweed & Hemp dogbane - All parts of the plant, whether green or dry, are poisonous to horses. The toxic properties are steroid glycosides and toxic resinous substances. Livestock generally avoid these plants unless other forage is unavailable. Hemp dogbane can be a threat to livestock in all seasons.
Ohio buckeye - Toxicity of buckeye nuts is attributed to glycosides (e.g., aesculin, fraxin), saponin (aescin), and possibly alkaloids. Sprouts and leaves produced in early spring and seeds can be especially poisonous. Note, experimental feedings have shown that poisoning does not always follow consumption of buckeyes.
Jimsonweed - All parts of the plant, and seeds in particular, contain tropane alkaloids (atropine, scopolamine, hyoscyamine). Because of the strong odor and taste, animals seldom consume enough of the green plant to be affected, but poisonings result from eating the dry plant in hay or silage, or from seeds mixed with grain.
Black Nightshade & Horsenettle - The glycoalkaloid, solanine, is produced in leaves, shoots, and unripe berries, and causes gastrointestinal irritation and central nervous system problems.
Ground Cherry - Leaves and unripe fruit are poisonous.
Johnsongrass - Hydrocyanic acid (cyanide) is produced in the leaves and stems of Johnsongrass when it is subjected to drought, trampling, frost, herbicide treatment, and even cutting.
Common Burdock - Is considered toxic due to potential diuretic effects, and there are reports of allergic reactions when the hooked bristles of burs lodge under the surface of the skin.
Pokeweed - All parts of common pokeweed are toxic to humans, pets and livestock. Roots are the most poisonous, leaves and stems are intermediate in toxicity (toxicity increases with maturity), and berries are the least toxic. Since common pokeweed is not very palatable, most animals avoid eating it unless little else is available, or if it is in contaminated hay. Horses, sheep and cattle have been poisoned by eating fresh leaves or green fodder.
Cocklebur - The plant is most hazardous at the seedling stage because of its toxicity as well as palatability. Ingestion of young seedlings in the amount of 0.75% of the animal's weight may result in clinical signs of toxicosis in a few hours and death in 24-48 hours. The seeds are poisonous at 0.3% of animal weight, but are seldom eaten because of their spiny capsule. Occasionally the eating of the ripe spiny capsules is said to result in intestinal obstruction.
If you have these plants in your pastured areas and available forage is dwindling, feeding hay is an option that should be considered. This may keep your livestock from ingesting poisonous forage and allow your wholesome forage plants critically needed extra time to regrow.
EDITOR's NOTE: For help in identifying pasture weeds, see the video posted below that was recorded by Mark Landefeld a few years ago.