Identifying Toxic Plants in your Pasture

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Identifying Toxic Plants in your Pasture
Erin D. Petersen, MS, PAS Extension Horse
SpecialistUniversity of Maryland-College Park
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Toxic Plant Management

• Most horses will not eat toxic plants if they
  have access to good quality forage
• Plants contain toxins to deter browsing
• To prevent browsing, the toxin makes the plant
  unpalatable

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Toxic Plant Management

• Always be aware of toxic plants. Be most
  concerned when
• Horses are undernourished
• Horses do not receive adequate forage
• Pasture grasses are no longer available due to
  overgrazing, drought, or changing seasons
• The plant has been know to cause poisoning in
  healthy horses

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Toxic Plant Management

• Toxicity can be difficult to diagnose
• Symptoms range from mild irritation to death
• Severity depends on
• Availability of the plant
• Toxicity of the plant
• Amount ingested

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Plants that are MILDLY toxic
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Alsike Clover
Alsike clover
White clover
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Alsike Clover
Conium maculatum

• Plant Characteristics
• Common in fields
• Prefers high moisture
• Clinical Signs
• Photosensitization
• Has potential to become seriously toxic Acute
  Liver Disease
• Toxin undetermined (fungus?)
• Treatment remove horse from source

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Buckwheat
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Buckwheat
Fagopyrum esculentum

• Plant Characteristics
• Grows in disturbed soils, roadsides, but rarely
  persisting.
• Toxin Fagopyrin (dianthroquinane)
• Reacts with ultra violet waves in the sunlight
• Present in both green and dried plant, not mature
  seed
• Clinical Signs
• Photosensitization, skin my slough off
• Treatment Remove animal from sunlight, treat
  with antihistamines/anti-inflammatories

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Buttercup
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Buttercup
Ranunculus spp.

• Plant Characteristics
• Thrives in soil with a low pH
• Prefers moist areas
• Safe when dried
• Toxin Protoanemonin (very bitter!)
• Clinical Signs
• Oral and gastrointestinal irritation
• Treatment Animals usually recover when removed
  from source

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Onions and Garlic
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Onions and Garlic
Alliumspecies

• Plant Characteristics
• Common weed found in pastures, and garlic is
  commonly added to equine diets for its insect-
  repellent qualities
• Toxin N-propyl disulphide (an alkaloid)
• Clinical Signs
• Pale mucous membranes fast, weak pulse
  staggering and collapse as a result of anemia
• Treatment Reduce stress, discontinue
  onion-feeding, whole blood transfusion in
  severely anemic animals

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Pokeweed
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Pokeweed

• Plant Characteristics
• Prefers rich, disturbed soils such as barnyards,
  moist woodlands and pastures.
• Toxin phytolaccatoxin and phytolaccigenin
• All parts poisonous, but especially the root and
  seeds
• Clinical Signs
• Gastrointestinal irritation, colic, diarrhea,
  rarely anemia
• Treatment treat symptoms, remove all sources of
  pokeweed from diet (including hay)

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Plants that are MODERATELY toxic
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Black Locust
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Black Locust
Robinia pseudoacacia, R. neomexicana

• Plant Characteristics
• Common ornamental tree
• Toxin Robin (properties similar to ricin)
• Leaves (especially wilted), young shoots, pods,
  seeds, inner bark (dose dependent!)
• Clinical Signs
• Colic, constipation, diarrhea, muscle weakness,
  irregular heartbeat
• May occur within one hour of eating
• Treatment
• prevent further ingestion, treat clinical signs

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Black Walnut
Edema of the legs and udder.
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Black Walnut
Juglans nigra

• Plant Characteristics
• Tree planted as windbreaks and along fence rows
• Toxin Unknown (juglone?)
• Clinical Signs
• Laminitis, colic, edema of lower legs
• Wood shavings with only 20 black walnut can
  cause laminitis
• Treatment Dont use shavings that include black
  walnut! Treat for laminitis (shoeing, etc)

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Brackenfern
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Brackenfern
Pteridium aquilinum

• Plant Characteristics
• Common in open woodlands, acidic, sandy or
  gravelly soil
• Toxin thiaminase
• All plant parts, especially roots
• Causes Thiamin deficiency
• Clinical Signs
• Blindness, depression, weight loss, inability to
  rise ? death
• A LOT must be ingested for clinical signs to
  occur!
• Treatment Daily thiamin injections for up to 2
  weeks

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Buckeye or Horse Chestnut
Aesculus spp.
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Buckeye or Horse Chestnut
Pteridium aquilinum

• Plant Characteristics
• Frequent ornamental and shade tree
• Toxins aesculin, fraxin and ?narcotic alkaloid?
• in leaves, seeds, young sprouts
• Poisoning in spring due to early sprouting
• Clinical Signs
• GI irritation, Neurologic signs
• Treatment supportive therapy

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Curly Dock
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Curly Dock
Rumex crispus

• Plant Characteristics
• Common in sandy soils, invasive in overgrazed
  pastures
• Toxin soluble oxalates
• Bind to calcium and magnesium in the blood
• Clinical Signs
• Muscle tremors, weakness, depression, recumbency
  kidney/liver failure
• Treatment I.V. Ca, Mg, glucose, electrolytes,
  Oral limewater to decrease further oxalation

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Hemp Dogbane
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Hemp Dogbane
Apocynum cannabinum

• Plant Characteristics
• Common along streams or wet, low-lying areas
• Spreads by rhizomes
• Toxins cynarin, apocynein (cardiac glycosides)
• In all plant parts, even when dried
• Poisoning is rare in horses
• Clinical Signs
• Diarrhea, colic, hemorrhagic gastroenteritis,
  abnormal heartbeat
• Treatment symptomatic therapy

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Horse Nettle
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Horse Nettle
Solanum carolinense

• Plant Characteristics
• Member of nightshade family all have similar
  toxicity
• Berries resemble green tomatoes
• Common weed of pastures and hayfields
• Toxin solanine (tropane alkaloid similar to
  atropine)
• Berries have higher levels of toxin not safe
  when dried
• Clinical Signs
• Salivation, colic, intestinal stasis, diarrhea,
  muscle tremors, weakness
• Treatment Symptomatic therapy
• Fluid therapy, activated charcoal via stomach
  tube. Physostigmine may be used cautiously in
  severely poisoned animals

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Milkweed
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Milkweed
Asclepias species

• Plant Characteristics
• Found in dry soils of roadsides, meadows, waste
  areas
• Toxin cardenolides (cardiac glycosides) - found
  in all parts of plant
• Clinical Signs
• Colic, incoordination, tremors, heart problems,
  respiratory difficulty
• Treatment supportive therapy

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Oak
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Oak
Quercus spp.

• Plant Characteristics
• Common shade tree
• Toxin gallotoxins
• New young leaves most toxic, acorns more toxic
  when green than when mature
• Clinical Signs
• Poor doer, poor appetite, weight loss, diarrhea
  or constipation, increased drinking, increased
  urination, edema, death is possible
• Treatment Aggressive fluid therapy avoid stress

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Rhododendron,Mountain Laurel, Azalea
Mountain Laurel
Rhododendron species
MountainLaurel
Rhododendron
Azalea
Rhododendron
Azalea
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Rhododendron,Mountain Laurel, Azalea

• Plant Characteristics
• Common wild or cultivated shrub
• Toxin grayanotoxins (glycosides)
• 0.2 by weight of green leaves needs to be
  ingested
• Clinical Signs
• colic, abnormal heart rate and rhythm,
  convulsions, coma, death
• Treatment Remove plants from animals supportive
  care

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Spurge
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Spurges
Euphorbia spp.

• Plant Characteristics
• Several varieties ranging from houseplants to
  ornamentals or weeds
• Toxin Diterpene esters in the milky sap, still
  toxic when dried but extremely unpalatable
• Clinical Signs
• Blistering and GI irritation
• Treatment Remove animals from spurge, they will
  recover uneventfully

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Tall Fescue
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Tall Fescue
Festuca arundinacea

• Plant Characteristics
• Common grass in pastures in this region
• Toxin Acremonium coenophialum (endophyte fungus)
• Clinical Signs Reproductive problems in mares
  ONLY fescue foot and summer slump in cattle
• retained placenta, prolonged gestation, agalactia
• Fescue foot lameness, dry gangrene (late
  fall/winter)
• Summer slump slower gains, ? milk production,
  poor appetite, retention of winter coat,
  reproductive problems, ? temperature
• Treatment Remove horses from fescue pasture 30
  days prior to foaling OR Domperidone per vet
  instructions (at least 10-15 days prior to
  foaling)

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Yellow and White Sweet Clovers
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Yellow and White Sweet Clovers
Melilotus spp.

• Plant Characteristics
• Drought tolerant weed found throughout the US
• Toxin Coumarin
• a vitamin K antagonist present in all parts of
  plant if improperly processed
• ONLY a problem if in moldy hay
• Clinical Signs
• Weak, anorexic, visible bleeding, pale mucus
  membranes, increased respiratory rates
• Treatment Vitamin K administration

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Plants that are EXTREMELY toxic
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Wild Black Cherry
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Cherry (Wild Black)

• Plant Characteristics
• Commonly grows in fence rows, roadside thickets,
  and rich open woods
• Toxin cyanide found in damaged leaves
• Clinical Signs
• Breathing difficulties, anxiety, staggering,
  convulsions, collapse, death
• Treatment
• Call a vet immediately (antidote available),
  reduce stress, remove animal from source

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Groundsel
A.k.a. Tansy Ragwort, Senecio
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Groundsel
Senecio vulgaris

• Plant Characteristics
• Prefer sandy soils
• Toxin Pyrrolizidine alkaloids
• All parts are toxic even when dried
• Clinical Signs
• Disrupts cell division, especially in liver ? a
  toxic dose of 15 mg of dried plant per kg
  bodyweight over 2 weeks induces severe,
  irreversible liver disease
• Can cause photosensitization, weight loss,
  jaundice
• Treatment unlikely toxin builds up in liver

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Hemlock (Poison, Spotted)
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Hemlock (Poison, Spotted)
Conium maculatum

• Plant Characteristics
• Found in areas where ground is moist common in
  fields, along roadsides
• Purple spots on stems
• Toxins coniine (mature plants/seeds) and
  gamma-coniceine (young plants)
• Toxic signs appear within 2 hours
• 4-5 pounds is lethal for a horse
• Clinical Signs
• Block spinal cord reflexes ? muscle tremors,
  incoordination, paralysis, frequent urination,
  sudden death
• Treatment supportive therapy

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Jimson Weed (Thorn Apple)
Datura stramonium
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Jimson Weed (Thorn Apple)
Datura stramonium

• Plant Characteristics
• Prefers disturbed soils in barnyards, cultivated
  fields
• Toxins Hyoscyamine, Hyoscine (scopolamine) and
  Atropine found in all parts of the plant
  (especially the seeds - horses may ingest seed in
  contaminated corn)
• Clinical signs
• Impaired vision, increased heart rate, agitation,
  convulsions
• Treatment Remove animals from weed contact vet
  there are medications that can counter-act the
  toxins

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Red Maple
Note red leaf stem on Red Maple
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Red Maple
Acer rubrum

• Plant Characteristics
• Common tree in many soil types
• Underside of leaves are white
• Toxin unidentified -- Toxicity is very high in
  wilted or dried leaves
• Ingestion of 1½ kg is toxic, 3 kg is lethal to
  horses (50-75 death/euthanasia rate)
• Clinical Signs
• Massive destruction of red blood cells ?
  breathing difficulties, jaundice, dark brown
  urine, death
• Wilted or dried leaves remain toxic for up to 1
  month
• Treatment Supportive therapy (mineral oil,
  activated charcoal, fluid therapy), possibly
  methylene blue

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Water Hemlock
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Water Hemlock
Cicuta maculata

• Plant Characteristics
• Prefers wet marshy sites, along streams, etc.
• Toxins Cicutoxin, and cicutol
• Found in all parts of the plant (especially the
  root)
• 8 ounces will kill a horse
• Clinical Signs
• Nervousness, breathing difficulties, muscle
  tremors, collapse, convulsions (seizures), death
• Treatment IV Sodium Phenobarbital, laxatives to
  speed removal from system

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Yew, English or Japanese
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Yew, English or Japanese
Taxus spp

• Plant Characteristics
• Common ornamental shrub
• Prefer humid, moist environments with acidic
  soils
• Toxin taxine (alkaloid)
• present in all plant parts, especially high in
  leaves during winter
• Clinical Signs
• Muscle trembling, incoordination, colic, slow
  heart rate resulting in death
• Typical presenting sign?
• One mouthful can kill a horse in 5 minutes
• Treatment supportive therapy if animal still
  alive, atropine to increase heart rate rarely
  successful.

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Take-home Message....

• Be careful when choosing ornamental plants for
  your farmyard
• Manage pastures for optimum growth of grasses,
  remove weeds when necessary
• Know the tree species in your pastures
• Provide plenty of palatable hay for your animals
  at all times!

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Useful Websites

• http//www.ansci.cornell.edu/plants/comlist.html
  -- Cornell University Poisonous Plant Database
• http//www.vth.colostate.edu/poisonous_plants/ -
  Colorado State University Guide to Poisonous
  Plants
• http//vet.purdue.edu/depts/addl/toxic/bytox1.htm
  - Purdue Toxic Plants by Degree of Toxicity