Plants Poisonous To Livestock In Montana And Wyoming - USDA

Photo: M. Lavin, MSUHalogeton (Halogeton glomeratus) has red stems and fleshyleaves. It has caused hundreds of livestock deaths in a singleday at one location in various western states. Livestock shouldnot be allowed to become hungry or thirsty while grazing in areasinfested with halogeton, as they will graze indiscriminately. Properrangeland management is the best way to minimize livestocklosses.Indirect losses include the following managementcosts: Building and maintaining fencesIncreased feed requirementsIncreased medical treatmentsAltered grazing programsDecreased forage availabilityDecreased land valuesIncreased stress on livestock managersIdentifying Poisonous PlantsThere is no single rule or characteristic that can beused to determine a toxic plant from a non-toxicplant. To protect animals from poisoning, learn toidentify poisonous plants that are common to the areaand obtain reliable information on their poisonousproperties. Some poisonous plant publications focuson plant identification; however, this publication doesnot because plant identification resources are readilyavailable. We provide a list of resources to aid inidentification in the Resources and References Sectionbelow.The maintenance of regular, detailed livestockmanagement records can be a useful tool whendiagnosing plant poisoning for an animal displayingsymptoms. For example, information about the dateanimals entered a pasture, where they moved from,their general health prior to symptom onset, andutilization of suspected plants can all be important. Ifthe animal is alive, careful observations and notes aboutits behavior should be made. If the animal has recentlydied, an inspection in the digestive tract (or a completenecropsy) for identifiable plant parts is recommended,along with an examination for abnormal-appearingorgans. Contact a veterinarian or other qualifiedindividual for help making a diagnosis. Whether ornot an animal is treated for plant poisoning may bedecided by behavioral observations, noted above, andby correct identification of the suspected poisonousplant. Ultimately, correct identification of the plant isessential for any long-term proactive corrective actionand should be considered an important starting pointif problems occur.When the presumed causal plant is identified, it shouldbe collected for verification by someone with plantidentification expertise. Collect the entire plant or, iftoo large, representative parts of the plant (roots, stems,leaves, flowers, fruits, and unique attributes). Recordinformation regarding date, location, habitat, plantsize, and plant growth characteristics. Photographsof the plant and its habitat are also useful. Soon aftercollection, press the specimen between two pieces ofnewspaper or cardboard to air dry. Alternatively, placethe plant in a bag in a refrigerator for short term storageif needed. If mailing the specimen for verification,place the pressed sample or bag in a padded envelopeor box. Use caution when handling specimens as someplants are toxic to humans too!Sudden onset of illness with no apparent cause mayindicate poisoning by a toxic plant. If plant poisoning issuspected, the responsible plant(s) must be identified,which is sometimes a difficult task. Symptoms may besimilar across multiple poisonous plants, all symptomsmay not manifest, and some symptoms may be atypical.Sometimes poisoning is even caused by a plant notcommonly recognized as toxic. Examine the rangelandor pasture for poisonous plant species.- 5 -Submit samples to one of the following: Local Extension or USDA-NRCS offices Montana State University SchutterDiagnostic Laboratory(http://diagnostics.montana.edu/) University of Wyoming Herbarium(http://rmh.uwyo.edu/data/search.php) USDA-ARS Poisonous Plant ResearchLaboratory ut/poisonous-plant-research/)

Factors Influencing Plant Toxicity to LivestockPlant-relatedSeason and Plant Growth StageDoseThe dose (i.e. amount consumed) needed for a plantto cause undesirable effects to livestock dependson factors like the amount and concentration of atoxin and how rapidly it is consumed. In plants, thedose is influenced by growing season, growth stage,palatability, and growing conditions. Some plantsare lethal after one exposure or a short duration oftime, other plants may require ingestion of largeamounts before affecting livestock, and other plantscause poisoning weeks or months after ingestion.Acute poisoning occurs when animals are exposed toa toxic dose on one occasion or for a short time andsymptoms are relatively instantaneous. For example,cattle or sheep consuming small amounts of poisonhemlock will exhibit symptoms of poisoning withinan hour. Chronic poisoning is long-term, repeated, orcontinuous exposure to a toxin. The toxins accumulatein the animal’s body over time, symptoms are delayed,and damage is usually irreversible. For example, cowsconsuming lupine during their early gestation periodmay show no evidence of poisoning until they givebirth to calves with cleft palates and skeletal defects(i.e. crooked calf syndrome).Information on what constitutes a toxic dose isonly available for commonly problematic species inMontana and Wyoming (Table 2), and, in many cases,is based on limited scientific research. The toxic dose isdependent on plant-related factors discussed below, aswell as animal-related factors such as animal health,species, and age.Photo: USDA-NRCSLupines (Lupinus spp.) have palmatelycompound leaves which radiate from a centralpoint. Lupine poisoning can be reduced bykeeping hungry animals away from lupine inearly growth stages and in late summer whenthe plant contains seeds that are very toxic.Poisonous plants vary in their toxicities and palatabilitywith season and growth stage. Rangeland and pastureshould be examined for the kinds, quantities, anddistribution of poisonous plants before livestock areallowed to graze. Some areas should be avoided duringthe most dangerous season if dense stands of poisonousplants grow there. For example, some plants are mostpalatable during their early growth stages, makingspring the most dangerous period for poisoning.Photo: M. Lavin, MSUChokecherry (Prunus virginiana) leaves have finely toothedmargins and a short, pointed tip. The toxic substance inchokecherry, hydrogen cyanide, is found principally in the leaves.Leaves become less toxic as the growing season progresses.Some poisonous plants are most toxic when they areimmature, others when mature, and still others areequally toxic at all growth stages (see Tables 1 and 2).Toxic substances are often concentrated in certain planttissues, and negative impacts may only be apparentPhoto: A. Oomen, bugwood.orgPhoto: T. Nelson, USDA-NRCSPoison hemlock (Conium maculatum) is 2 to 20 feet tall with white flowers,finely dissected leaves, and purple spots on the stem. Livestock poisoningis most common in the early spring when tender, succulent, highly toxicnew leaves begin growth.- 6 -

when consumed at the time of year when these tissuesare available. For example, plants with toxins mostconcentrated in seeds should not be grazed duringseed development and ripening.PalatabilityPalatability is important because it determines livestockutilization of poisonous plants. Many poisonous plantsare not very palatable, so animals will usually selectmore palatable, non-poisonous species. If an area doesnot offer enough palatable non-toxic forage, however,animals are more likely to consume toxic quantitiesof poisonous plants. In addition, palatability is highlyvariable and can change over the growing season orin response to recent climatic events (e.g. frost) orvegetation management. For example, many species,including poisonous plants, are more palatable for afew weeks following herbicide or fertilizer application.problem can be exacerbated by a lack of palatableforage during drought which can cause livestock to eatany plant available, even species with toxic properties.The concentration of different elements in soil caninfluence several species of poisonous plants. Forexample, certain species of saltbush and milkvetchgrowing in soils high in selenium accumulate toxicquantities of this element, whereas the same saltbushspecies may provide good forage on soils low inselenium.Photo: M. Lavin, MSUShadscale saltbush (Atriplex confertifolia) has grayish bark,alternate leaves, and fruits with four conspicuous wings. Itaccumulates high levels of selenium when growing in selenium-richsoils and can cause chronic selenium poisoning when consumedby livestock .When certain species grow in the same vicinity andare grazed in combination, toxic effects can vary. Forexample, sheep feeding on horsebrush just followingor in conjunction with black sage and then exposed tobright sunlight may develop a characteristic swellingof the head called bighead (i.e. photosensitization).Sheep grazing horsebrush alone may experience toxicimpacts without developing bighead.Component of HayPhoto: K. Clause, NRCSArrowgrass (Triglochin maritima) has fleshy, darkgreen, grass-like leaves and a slender flower stalk.Arrowgrass plants quickly become toxic whenstressed or damaged from drought, frost, or cutting.Foliage that re-grows following harvest is also toxic.Growing ConditionsPlants growing during stressful conditions (e.g.drought, freezing) commonly have increased toxicitylevels. For example, arrowgrass grown with adequatemoisture does not cause hydrogen cyanide poisoning,but when growth is stressed or stunted from inadequatemoisture, arrowgrass quickly becomes toxic. ThisPlant toxicity may increase, decrease, or remainstatic when foliage dries. This factor and the plant’sstage of development when harvested, is importantin determining toxicity of hay containing poisonousplants. When poisonous plants are mixed with nonpoisonous plants and fed together in hay, livestockare unable to discriminate between them as readilyas when grazing in a field and are consequently morevulnerable to poisoning. Areas containing substantialamounts of poisonous plants should not be hayed, andhay containing poisonous plants should not be fed tolivestock without consulting with the local Extensionagent, NRCS employee, or another qualified person.- 7 -

Photo: T. Nelson,USDA-NRCSexample, ingestion of ponderosa pine needles by malecattle appears harmless while it may cause abortionsin pregnant females. Additionally, the size of animalswithin a class of livestock may be proportional tothe quantity of toxin required to cause poisoning. Asanimal size increases, the amount of poisonous plantneeded to be consumed to cause toxicity symptomsalso increases. Younger animals are usually moresusceptible to poisoning than older animals. It has beenshown that yearling steers may be more susceptible tolarkspur poisoning than two-year-old steers.Photo: USDA-NRCSHorsetail species (Equisetum spp.) have hollow, jointed stems,and grow in moist to wet meadows and pastures. Horsetail canhave whorls of branches at the joints (left photo) or a single,unbranched stem (right photo). It is often cut and incorporated inhay where it retains toxic properties when dry. Cattle or horsesfed hay containing more than 20% horsetail can experiencegastrointestinal and nervous system poisoning effects.Animal HealthAnimal-relatedAnimal Species, Gender, Size, and AgeSome poisonous plants have a more negative effect onone specific class of livestock, while other plants areequally toxic across all classes. Different classes oflivestock preferentially graze certain types of plants.For example, cows and horses prefer grasses, whilesheep prefer forbs and shrubs. Rangeland and pastureshould be inspected for the kinds and quantities ofpoisonous plants before grazing. This informationcan be used to decide what class of livestock shouldbe grazed. Livestock losses may be prevented bygrazing those animals that will not be harmed bythe poisonous plants present. Also, skin color candetermine susceptibility of animals to photosensitivityafter eating certain poisonous plants. For example,light- to white-skinned individuals (Hereford cows,white-faced horses) are more photosensitive and willsuffer sunburned faces or udders.Animals within the same livestock class or breedmay vary in their susceptibility to plant toxicity. Forexample, in a study that dosed Angus steers withlarkspur and then imposed the steers to stressfulconditions, 40% were considered resistant and theremaining 60% were too sensitive to even imposethe stress without risk of death. Livestock in poorcondition or subjected to adverse conditions or stress(e.g. temperature, exertion, etc.) are usually moresusceptible to poisoning than non-stressed animalsin good condition. Hungry animals may ingest higherquantities of a poisonous plant, while satiated animalsare more selective and tend to consume lower doses ofa toxic plant. In general, an animal will consume lesspoisonous plant tissue when it can graze selectively.Toxicity to some poisonous plants is gender-specific,particularly as it pertains to animal reproduction. ForPhoto: M. Lavin, MSUPhoto: M. Lavin, MSUMilkvetch species (Astragalus spp.) have pea-shaped flowers andgrow in a variety of native habitats. Many milkvetch species cancause acute or chronic poisoning of livestock. Cattle will readily eatsome toxic milkvetch species even when other forage is available.To reduce livestock losses, prevent animals from grazing theseplants for extended periods, feed protein supplements, and avoidstressing cattle that have grazed toxic milkvetch species.Photo: USDA-NRCSPonderosa pine (Pinus ponderosa) can causeabortions during the last trimester of pregnancy ifcattle graze approximately 5 to 6 pounds of needles.The needles are generally grazed during the winterwhen forage is lacking or snow-covered. Preventpoisoning by limiting access to ponderosa pine duringthe last trimester.Animal Response to ToxinSome toxins quickly change to harmless substancesupon ingestion or are rapidly eliminated after enteringthe body and are therefore usually of little danger toan animal. Alternatively, toxins rapidly absorbed intothe animal’s circulatory system following ingestion arevery dangerous.- 8 -

Conditions Leading to Livestock Poisoningand Management to Reduce ImpactsThe most effective way to prevent livestock loss frompoisonous plants is to properly manage rangeland,pasture, forest, and livestock. Develop a grazing planthat improves or maintains rangeland or pasturecondition and prevents poisoning. Plans shouldconsider poisonous plants in the

Plants Poisonous to Livestock in Montana and Wyoming. represents a cooperative effort among individuals within . the United States Department of Agriculture - Natural Resources Conservation Service (USDA-NRCS), Montana State University (MSU) Extension, and University of Wyoming (UW) Extension. This publication is adapted with