However, some plants are cause for concern either because even a curious nibble can spell doom or because repeated browsing over weeks or months can lead to serious illness and death. Best eliminated and certainly not to be sown. It appears to be much more poisonous to horses than to humans. And, as disquieting as it may be to contemplate, the chances are pretty good that at least some are toxic to horses. For one thing, most of them are unpalatable, and horses who are filling up on quality forage aren't likely to spend a lot of time grazing on the few bitter leaves populating their pasture. This means that your horse will get just as ill from eating small amounts of ragwort over a long period of time as it would do from eating a large quantity in one go. www.equinestudies.org. Heart rhythm irregulairties, heart block, rapid breathing, weak and irregular pulse, diarrhoea, colic and cold extremities. Take a stroll through any pasture, and there among the grasses you'll find any number of different plants. You too have probably seen them devour them prickles and all! Access to wilted leaves is most common after storms, which may cause branches to fall into pastures, or in the autumn when the leaves fall and are blown into grazing areas. This will usually sterilize the seeds and prevent the seed heads from becoming sharp/brittle. It is thought that only horses experience poisoning by the plant; cattle, mules and burros do not appear to be affected by it. Bracken fern (Pteridum aquilinum) Also known as: brake fern, eagle fern. So the grass itself is not toxic, but the seed-heads are a problem when parasitized by the ergot fungus which can produce toxic ‘pyridine alkaloids’ (nasty chemicals) in the little ‘mouse-droppings’ that appear in late summer or autumn. The good news, of course, is that the vast majority of those plants pose little threat to horses. Canada thistle produces nitrate which can be toxic to your horse in high doses. Some grasses and weeds are just better off not being allowed in the paddock at all! Russian knapweed spreads via a creeping root system; its erect, stiff stems grow two to three feet high and are covered with gray hairs, and its thistlelike flowers range from purple to white; Russian knapweed has no spines or prickles.Range: Both plants appear throughout the Western United States, approximately from Missouri to California, and from Mexico northward, almost to Canada. The poisoning is chronic in nature; to receive a toxic dose, horses must consume 50 to 200 percent of their body weight over 30 to 90 days.Signs: Affected horses may appear to have tense or clenched facial muscles, and they are unable to bite or chew their food effectively. As disquieting as it may be to contemplate, the chances are pretty good that at least some are toxic to horses. Horses are considered the least susceptible animals to nitrate poisoning. Dandelions have a thicker single flower on a single thicker stem whilst the Cat's Ear has a branched stem with multiple little flowers. [Read up on horsekeeping and horse health]Horse Owner's Veterinary HandbookStorey's Barn Guide to Horse Health Care + First AidHorse Health Care: A Step-By-Step Photographic Guide to Mastering Over 100 Horsekeeping Skills, Horsekeeping on a Small Acreage: Designing and Managing Your Equine FacilitiesThe Merck Veterinary Manual[Disclaimer: EQUUS may earn an affiliate commission when you buy through links on our site. Yahoo is part of Verizon Media. It will cause reproductive problems in horses too especially when the horses have nothing else to eat! Horses with less severe poisoning may recover when access to the weed is removed. "I defy anyone to tell me they have a pasture with zero poisonous plants," says Jeffery Hall, DVM, PhD, a toxicologist at Utah State University. Also known as: Rose laurel, adelfa, rosenlorbeerID: An evergreen shrub that can reach the size of a small tree, oleander has elongated, thick leathery leaves that can grow to three to 10 inches long. They recover in a few days if removed from the infected pasture. The toxin levels in the leaves and stems diminish as the plant ages during the growing season, and additional amounts of toxin are lost when the plant is dried, but water hemlock is never considered safe for consumption. Most of the information contained about these plants comes from the excellent 2008 DVD ( Poisonous Plants in the Pasture: A Horse Owners Guide) put together by Dr Deb Bennett PhD which can be obtained from her website at The estimated nitrate lethal dose is 61 grams to 152 grams per animal. The plants' name comes from its unique underground seed development, different to other clovers. It is a small leaf clover and has little white flowers in the spring. Grows in clumps in woodlands and moist open areas.Range: Coast to coast, except for the Mediterranean and desert climates of Southern California and the Southwest.The danger: Bracken fern contains thiaminase, which inhibits absorption of thiamin, which is vitamin B1. They're mostly on disturbed sites, roadsides, and waste ground, but they can also establish on rangeland, pasture, and natural areas.They germinate and grow into rosettes during winter, then in spring they bolt and produce purple flowers. It is another reason to do the annual broad-leaf spray off as the same spray that gets rid of clover will also eliminate this potential nasty. It does well in poor-quality soil where other clovers cannot survive. Affected animals exhibit muscle tremours, move with s atsiff gait and arched back. A third problem, often confounded by the first two, arises from alkaloids produced not by the lupine itself, but by a fungus that grows on lupine pods and stems. LOW endophyte rye grass are Rye-grasses that have been artificially modified to either eliminate the endophytes altogether (Zero-endophyte) or just the most toxic endophytes while retaining the less toxic ones (Low-endophyte) for protection against insect damage to the grass.