Pasture Management and Toxic Plants

Qualitites of a good pasture

• Highly palatable

• High nutrient value

• Withstand climate extremes

• Good moisture content

• High leaf-to-stem ratio

• Fast regeneration

How to maintain a good pasture

• Ability to rest pasture after grazing

• Limit pasture access during periods of wet weather

• Prevent overcrowding

Stiuations that lead to toxic plant poisonings

• Animals moved to new pasture when hungry

• Pasture sparse due to overgrazing

• Poor growth in spring, or drought conditions

• Herbicide application to control weeds

• Recent nitrogen fertilizer application

• New forage source (hay, silage)

Most common toxicosis in large animals next to feed additives

ingestion of toxic plants

Toxins in pasture plants

• Most common toxicosis in large animals, next to feed additives

• Toxic plants taste bad!

• Your role: educate client and help identify plants

• Good refs are available

• Toxin Principle…

The saying about toxins

“The dose makes the poison”

Toxin concentrations and vary based on

• Plant: Type and part

• Growing season

• Location

Toxin concentration variations - Plant

• Type

  • Wild - weeds, forages

  • Landscape cultivars

• Part

  • Root

  • Stem

  • Leaf

  • Fruit/seed

Toxin concentration variation - Growing season

• Time of year

• Conditions - wet, drough

Toxin concentration variation - Location

• Region of US

• Section of pasture

Classifications of toxins

• Nitrates

• Oxalates

• Gallotannins

• Glycosides

• Phototoxins

• Cicutoxins

• Alkaloids

• Ketones

• Mycotoxins

• Enzymes

• Misc - Topical, mechanical

How nitrates break down

• They are reduced to nitrites in the intestinal tract

  • Mostly affect ruminants

• Nitrites bond to hemoglobin, forming methemoglobin

  • Bonds tightly to oxygen; not released to tissues

  • Acute

    • Trembling

    • Tachypnea

    • Ataxia

  • Chronic

    • Poor growth

    • Decreased milk production

    • Abortions

Nitrates

• Plants fix nitrogen from soil; accumulates with plant stress

  • Weather extremes, low light, herbicide application/disease

• Ingestion of plants with extremely high  nitrate content

  • Any nitrogen fixing plants - legumes (alfalfa, clover, soybeans, peanuts)

  • Periods of drought

  • Nitrogen fertilizer application

Oxalates

• Excess amounts of oxalate bind to calcium causing calcium oxalate crystal formation

  • Hypocalcemia

  • Hyperoxaluria

    • Influx of crystals damage renal tubules

    • Kidney stone formation

Who is more tolerant of oxalates

• Ruminants typically more tolerant than non-ruminants

  • Rumen bacteria degrade oxalate into harmless formic acid and cardon dioxide

What plant is this?

Pigweed (Amaranthus sp.)

Pigweed toxins

Nitrates and oxalates

Clinical signs and Treatment of pigween toxicity

• Perirenal edema - pigs, some cattle

  • Straw colored fluid in/around kidneys

  • Ascites/hydrothorax/edema

• Renal toxicity - necrosis, increased BUN, Creat

• Coma/death 2-15 days

• Supportive care

• Remove access to plants

Key characteristics of Pigweed

Large seed head - late summer, fall

What plant is this?

Rhubarb (Rheum rhabarbarium)

Key characteristics of rhubarb

• Large, board leaves

• Red stems

Toxins in Rhubarb

• Oxalic acid concentration in leaves (stems ok)

• Ruminants are more tolerant, but still a concern

Clinical signs and treatment in rhubarb toxicity

• GI: mouth/stomach irritation, abdominal pain, vomiting

• Musculoskeletal: tremors, weakness

  • Hypocalcemia - oxalates bond to blood calcium

• Renal: PU/PD, blood in urine

  • Calcium oxalate precipitates in renal tubules - nephrosis

  • Acute renal failure

• Supportive care

  • IV fluids - calcium gluconate

  • Lavage/Gastroprotectants

Nitrate and Oxalate plants

• Pigweed

• Rhubarb - only oxalate

Positive effects of Gallotannins

• Anti-inflammatory

• Antibacterial

• Antitumor

• Modulation of hemostasis

• Reduce production of toxic metabolites

Gallotannins

• Tannins have been found in a variety of plants, fruits, wines, forages, and tea

• Gallotannins (oak) and ellagitannins are the most widely occurring tannins

What plant is this?

Oak (Quercus sp.)

Toxins in Oak

• Tannins

• Highest concentration in young leaves (spring), oak buds, unripe green acorns (autumn)

Clinical Signs of Oak toxicity

• Initial GI signs

  • Loss of appetite, black feces, diarrhea with blood

  • Weak, rapid pulse

• Lethal kidney toxicity

  • Gallotannins convert to tannic acid and gallic acid

  • Frequent urination

Treatment for oak toxicity

• Supportive care

  • IV fluids

  • Laxatives

• Surgery

  • Rumenotomy/gastric lavage

  • Prevent by feeding quality forage

What plant is this?

Red maple (Acer rubrum)

Key characteristic of red maple

• Smooth to moderate rough bark

• Red petiole

  • Differentiate from silver/sugar maple

• Horticulture cultivars not toxic

Toxins in red maple

• Gallic acid?

• Wilted leaves

Clinical Signs of red maple leaf toxicity

• Only horses affected - remember clin path

• Initial GI signs

• Lethal kidney toxicity

  • Hemoglobin released from lysed RBCs (hemolysis)

  • Heinz body anemia and hemoglobinuria

• Blood - decreased oxygen carrying capacity

• Liver - icterus

Treatment of Red maple leaf toxicity

• Maintain kidney function and tissue oxygenation 1st

  • Isotonic fluids to remove precipitate and flush renal tubules

  • Blood transfusions to increase oxygen carrying capacity

• Supportive care

  • Activated charcoal, NSAIDS

Gallotannin plants

• Oak

• Red maple

Different glycosides

• Cyanogenic (cyanide)

• Mustard Oil

• Saponin

• Coumarin Glucosides

Cyanogenic Glycosides (cyanide)

1. Hydrolysis of certain enzymes during digestion produce hydrogen cyanide (prussic acid) - HIGHLY TOXIC

2. Prevents oxygen exchange with body tissues/brain

   • Respiratory: difficult, rapid respiration

   • CNS: muscle tremors, convulsions

3. Death occurs in MINUTES

Mustard Oil Glycosides

GI: severe vomiting, colic

Saponin Glycosides

1. GI: severe vomiting, diarrhea, colic

2. Bloodstream: breakdown RBCs

3. CNS: convulsions, paralysis

Coumarin Glucosides

Glycoside chemically derived from glucose

What plant is this?

Cherry tree (Prunus sp.)

Toxin in Cherry tree

Cyanide - conversion of glycoside

Clinical signs and treatment of Cherry tree toxicity

• Rapid progression - excitement, tremors, convulsions, death (minutes)

• First sign may be dead animals in pasture

• Prevent access to pastures with down limbs or wilting leaves (Autumn)

What plant is this?

Ohio Buckeye Horse Chestnut tree (aesculus sp.)

Key characteristics of Ohio buckeye horse chestnut tree

• Palmate five leaflets

• Yellow flowers at end of branch

• Prickly fruit with glossy brown seed

Toxin in the Ohio Horse Chestnut Tree

• Aesculin - coumarin glucoside

• Buds, nuts, leaves, bark, seedlings

Clinical signs and treatment of Ohio Buckeye Horse Chestnut tree toxicity

• GI signs in monogastric

  • Salivation, vomiting, abdominal pain, diarrhea

• Neurological signs in ruminants

  • Trembling, ataxia, difficulty breathing

• Signs rarely severe, however poor prognosis if progresses to coma

• Supportive care

  • Laxatives

  • IV fluids

What plant is this?

Grain Sorghum - Millet (Sorghum bicolor)

Key characteristics of Grain Sorghum

• Large seed head

• Slender leaves

Toxin in Grain Sorghum

Can contain toxic levels of cyanide and nitrates

Clinical signs of Grain sorghum toxicity

• Ruminants rapidly absorb cyanide and nitrite ions - "brown blood"

• Cyanotic membranes (hypoxia)

• Dyspnea

• Weakness/tremors

• Ataxia

• Respiratory/cardiac arrest

What plant is this?

Johnsongrass (Sorghum halepense)

Key characteristics of johnsongrass

• Coarse perennial grass

• Heights up to 8 ft

• Large, open seed head

• Often has brown blotched on leaves

Toxin in Johnsongrass

• Can contain toxic levels of cyanide, nitrates, and hordenine (alkaloid)

• Early growth - dark green leaves

CLinical signs of Johnsongrass toxicity

• Anxiousness/stress

• Deep, rapid breaths

• Trembling/incoordination

• Respiratory/cardiac arrest

Glycoside Plants

• CHerry tree

• Ohio Buckeye Horse Chestnut Tree

• Grain Sorghum - Millet

• Johnsongrass

Photosensitization

When an animal become sensitive to sunlight

Primary Phototoxin

• Sensitize the skin through contact or ingestion

• Unpigmented (white) skin affected

• Sunburn, swelling, ulcers, blindness

Hepatogenic phototoxins/hepatotoxins

• Toxins damage liver

• Prevents phylloerythrin

Cicutoxin

Severe convulsant

Cicutoxins

• Cicutoxin - severe convulsant

• Causes death by respiratory paralysis resulting from disruption of the CNS

• Potent, noncompetitive antagonist of gamma-aminobutyric acid (GABA) receptor

What plant is this?

St. John’s Wort (Hypericum sp.)

Key characteristics of St. John’s Wort

• Shrub up to 6' tall, 3-5' wide

• Five petal bright yellow flowers

• Readily eaten by cattle

Toxin in St. Johns Wort

• Hypericin

• Affects all species

Clinical Signs of St. John’s Wort toxicity

• Photosensitization of non-pigmented skin

  • Easily sunburned

  • Rash, blisters

Treatment of St. John’s Wort toxicity

• Get animal into shade

• Topical treatment based on severity

• Pain management

Phototoxins/Hepatotoxin Plant

St. John’s Wort

What plant is this?

Water Hemlock (Cicuta maculata)

Key characteristics of Water Hemlock

• Carrot family- carrot-like odor (not definitive)

• White flowers - umbrella clusters

• Narrow, serrated leaves

• Stem has hollow core

• Can get confused with queen anne’s lace plant

Toxin in Water Hemlock

• Cicutoxin

  • Extremely poisonous

  • Toxic at all growth stages - decreases through growing season

  • Root/tuber most toxic

  • Horse eating 8 oz. is lethal

Clinical signs of Water Hemlock toxicity

• CNS - Stimulant, fits, convulsions

  • Hypothermia secondary

  • Respiratory paralysis

  • Rapid progression to coma, death (2 hrs)

Treatment of Water Hemlock toxicity

• Extremely poor prognosis

• Anticonvulsants

• Supportive care

Cicutoxin Plant

Water Hemlock

Alkaloids

• Organic, basis, bitter taste

  • Atropine

  • Nicotine

  • Strychnine

  • Morphine

Alkaloids effect on GI tract

Irritation

• Nausea

• Diarrhea

• Colic

Alkaloids act on CNS

• Muscle weakness

• Blindness

• Convulsions

• Death

Ketones

When these are produced too quickly and build up in the blood, they can be toxic by making the blood acidic

Mycotoxins

• Produced by fungi infecting the plant, not the plant itself

• Certain environmental conditions must be met

  • White growing in field

  • After harvest when stored

What plant is this?

Yew (Taxus sp.)

Key characteristics of Yew

• Dark evergreen shrub

• Flat needle leaves

• Red cupped berry

Toxin in Yew

• Taxines (A, B), Paclitaxel (Taxol), Hydrocyanic esters, Ephedrine

• Highly toxic in ALL SPECIES (including humans)!

  • Toxic dose in cattle 0.5% of bodyweight

• Toxic fresh or dried

Clinical Signs of Yew toxicity

• RAPID ONSET - Often found dead, 24-48 hr post ingestion

• Cardiac - bradycardia, acute cardiac failure

Treatment of Yew and Poison Hemlock toxicity

• Supportive - often futile

  • Immediate emesis or gastric lavage

  • Activated charcoal and cathartic (MgSO4)

  • Atropine for bradycardia

    • What's the downside to using atropine?

• Surgery - rumenotomy

• Prevention is key

What plant is this?

Poison Hemlock (Conium maculatum)

Key characteristics of Poison Hemlock

• Very tall!

• In carrot family - looks, smell

• Broad flowering head with many clusters of small white flowers

• Purple blotches on stem definitive ID

Toxin in Poison Hemlock

• Nicotinic alkaloid - nicotinic receptors within CNS @ neuromuscular junction

• Entire plant - toxicity INCREASES through growing season

• Roots and seeds highly toxic year round

• Horse consuming 4-5lbs is lethal

Clinical Signs of Poison Hemlock in toxicity

• RAPID ONSET - often found dead, 24-48 hr post ingestion

• Cardiac - bradycardia, acute cardiac failure

• CNS - trembling (overstimulation leading to paralysis (nicotinic receptor lockup at NMJ)

What plant is this?

Jimsonweed (Datura sp.)

Key characteristics of Jimsonweed

• "red as a beet, dry as a bone, blind as a bat, and mad as a hatter"

• "Loco weed"

• Spikey leaves

• Spikey seed pod

Toxin in Jimsonweed

• Hyoscyamine, hyoscine, atropine - high doses

  • Alkaloid and anticholinergic

  • Atropine toxicity

• Hallucinogenic at high doses

• Smoking seeds/drinking tea has killed teenagers

Clinical Signs of Jimsonweed toxicity

• CNS: Dilated pupils

• Circulatory: Tachycardia

• Musculoskeletal: muscle twitching, restlessness

Treatment of Jimsonweed toxicity

• Parasympathetic stimulator drugs

  • Pilocarpine

  • Physostigmine

What plant is this?

Nightshades (Atropa sp.)

Key characteristics of Nightshades

• Purple flowers with yellow center

• Small green fruit turning to shiny red or black

Toxin in Nightshades

• Tropane alkaloids - anticholinergic properties

• Highest concentration roots, foliage and GREEN berries

• Mature berries least toxic, sweet taste

Clinical signs of Nightshade toxicity

• NS - weakness, coma, resp paralysis, death

• Disruptions of PSNS to regulate involuntary activity

Treatment of nightshade toxicity

• Same as for atropine - Parasympathetic stimulator drugs

  • Pilocarpine

  • Physostigmine

Alkaloid plants

• Yew

• Poison Hemlock

• Jimsonweed

• Nightshade

What plant is this?

What Snakeroot (Eupatorium rugosum)