Plant Poisons

Exposure

• browsing tendency of animals

  • animals in feedlots “bored”

  • animals pastured in or near woodlots, tree lines, etc.

• accidental ingestion

  • incorporation of material into stored feeds

  • animals forced to consume plants they would not consume voluntarily

• starvation - limited feed resources

• learned behaviors - animals need to “learn” what not to eat

Factors affecting plant toxicity

• amount of plant material consumed

• part of plant material consumed

  • roots, stems, leaves, fruits

• growing conditions

  • drought - increases nitrates, prussic acid

  • wilting of leaves - increases cyanide in the leaves of wild cherry

  • recent use of herbicides

Cyanogenic plants

• contains non-toxic cyanogenic glycoside

  • hydrolysis of glycoside releases free cyanide, HCN

• HCN interferes with oxygen transfer from RBC to tissues, depriving tissues of oxygen (binds to hemoglobin and prevents release of O₂)

• pathognomonic sign: venous blood is bright “cherry” red

Common cyanogenic plants

• all members of the Prunus family: wild cherry, choke cherry, etc.

• sudan grass

• sorghum

• arrow grass

• Johnson grass

Cyanogenic toxicity is influenced by …

• age and size of the plant

  • younger, shorter plants are more toxic

• growth conditions

  • drought increases glycoside

• wilting and frost

  • increases hydrolysis to HCN

• storing method

  • ensiling is usually safe

  • hay may or may not be toxic

Nitrate accumulators

• nitrates bind to hemoglobin and block O₂ from binding → methemoglobin

• wide variety of agricultural plants and weeds are capable of accumulating nitrates

  • corn, sorghum, sudangrass, timothy

  • small grains - oats, rye

  • weeds: lamb’s quarter, Jimson weed, sweet clover, smartweed, thistles, pigsweed

Factors affecting plant nitrate concentration

• plant species - nitrate accumulators

• chemical form of nitrogen fertilization

• moisture content of the soil

• soil pH

• plant growth phase

  • some plants may accumulate nitrates while dying following herbicide application

• nitrate reductase activity → helps convert nitrate to ammonia

  • requires Mo, S, P, and light

  • frost and drought decrease the activity of this enzyme, making nitrate more prevalent in the plant

Prevention of nitrate toxicity

• recognize the risk factors for agricultural plants

• limit exposure to weeds of concern

• monitor forage nitrate content

• adapt animals to feed

• ensure sufficient fermentable carbs in diet

Alkaloids - overview

• nitrogen containing compounds, basic in nature, heterocyclic ring

• produced in plants from amino acids

• many have medicinal uses

Nightshade family

• solanine is the alkaloid

• causes GI and nervous clinical signs

Hemlock family

• piperidine alkaloids - coniine

• CNS and teratogenic effects

• poison hemlock common in roadside banks and fence lines

Pyrrolizidine alkaloids

• accidental poisoning from hay and silage

• a hepatotoxin

• horses are very sensitive to this toxin

Taxine

• taxol is the toxic compound

• highly toxic to many species

• toxic alkaloid affects many systems

  • GI, respiratory, CNS, cardiovascular

• typically presented as “sudden death”

• often “accidental” from plant trimmings placed in pasture or feedlots

Soluble oxalates

• can cause kidney damage

  • oxalate crystals in kidney cause tubular necrosis

• binding of minerals

  • acute hypocalcemia

• curly dock, lamb’s quarter, pigsweed

Insoluble oxalates

• local irritant

  • oral, pharyngeal lesions

• dumb cane

Cardiac glycosides

• increase strength of cardiac muscle contractions

• useful at low doses, toxic at higher doses

• plants:

  • foxglove (digitalis)

  • milkweed

  • oleander

  • Lily of the Valley

Photosensitization

• necrotic dermatitis in non-pigmented skin due to UV activation of plant-based compounds deposited in the dermis

• common plants: St. John’s Wort, Buckwheat, etc.

Tetrahydrocannabinol

• Plant: cannabis sativa

• increased reporting of intoxication in pets in states that have legalized recreational and medicinal use

• typically a result of consumption of the compound rather than inhalation

• signs: incoordination and listlessness, dilated pupils, slow heart rate, urinary incontinence

• sedation and supportive care works best as treatment

Mustard Oils

• Brassica family

• cause anemias, and are goitrogenic

Thiaminase

• ex. Bracken fern, common horsetail

• thiamine deficiency signs

Tremetol

• white snakeroot

• excreted in milk

Coumarin

• sweet clover poisoning

• interferes with blood clotting

Common pet poisonings

• chocolate

• onions and garlic

• xylitol

• high salt food and products

• coffee grounds

• household plants

• grapes and raisins

• macadamia nuts

• antifreeze

• drugs

• marijuana

• rodenticides