pasture management & toxic plants

what are the qualities of a good pasture?

• highly palatable

• high nutrient value

• withstand climate extremes

• good moisture content

• high leaf-to-stem ratio

• fast regeneration

how can you maintain a good pasture?

• ability to rest pasture after grazing

• limit pasture access during period of wet weather

• prevent overcrowding

what are the situations that lead to toxic plant poisoning?

• 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)

besides feed additives, what is the most common source of toxicosis in large animals?

toxins in pasture plants/toxic plants

what is the toxin principle? explain.

“the dose makes the poison” → all food is somewhat toxic, just in small amounts though, but if you ingest a lot of it, that’s when it becomes a problem

how can toxin concentrations vary?

vary by:

• the type or part of a plant

• growing season

• location

what are the 11 classifications of toxins?

1. nitrates

2. oxalates

3. gallotannins

4. glycosides

5. phototoxins

6. cicutoxins

7. alkaloids

8. ketones

9. mycotoxins

10. enzymes

11. misc. → topical, mechanical

T/F - nitrates mostly affect ruminants because they’re converted to nitrites in the intestinal tract

true

how do nitrates change RBCs?

nitrites bond to hemoglobin → becomes methemoglobin

T/F - ruminants are less tolerant to oxalates than non-ruminants

false → ruminants are more tolerant to oxalates than non-ruminants

how do oxalates cause changes in urine?

excess calcium leads to calcium oxalate crystal formation

what is the key characteristic to identifying pigweed?

large seed head

what toxin does pigweed have?

nitrates & oxalates

what are the clinical signs of pigweed poisoning? what species are most commonly affected?

• perirenal edema

• renal toxicity

• coma/death within 2-15 days

  • pigs, some cattle

what is the key characteristic to identifying rhubarb?

• large, broad leaves

• red stems

what parts of the rhubarb plant are safe/toxic?

• safe = stems

• toxic = leaves due to oxalic acid concentration

what happens physiologically to an animal that ingests rhubarb?

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

• musculoskeletal: tremors, weakness (hypocalcemia)

• renal: PU/PD, blood in urine

  • calcium oxalate causes nephrosis

  • acute renal failure

what are the 2 most widely occurring tannins? which one is oak?

1. gallotannins → oak

2. ellagitannins

what issues arise from ingestion of oak leaves? how can this issue be avoided?

• 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

• avoided by: feeding quality forage

what species is affected by red maple toxicosis?

equine

what are the clinical signs of red maple toxicosis?

• initial GI signs

• lethal kidney toxicity

  • hemoglobin released from lysed RBCs

  • heinz body anemia & hemoglobinuria

• blood - decreased oxygen carrying capacity

• liver - icterus

what is the key to identifying red maple from other maple species?

their stems

• red = red maple

• green = sugar maple

• silver/white/pale = silver maple

why is red maple toxic? what happens to the patient physiologically?

• gallic acid + wilted leaves

• anemic + icteric

what are the 4 types of glycosides?

1. cyanogenic glycosides (cyanide)

2. mustard oil glycosides

3. saponin glycosides

4. coumarin glucosides

which of the 4 glycosides is most dangerous and why?

cyanogenic glycosides (cyanide) → prevents oxygen exchange with body tissues/brain

what happens when wilted choke cherry tree leaves are ingested by ruminants?

excitement, tremors, convulsions, death :(

what are key characteristics of the ohio buckeye/horse chestnut tree? what parts are toxic?

• key characteristics:

  • palmate five leaflets

  • yellow flowers at end of branch

  • prickly fruit with glossy brown seed

• toxic: buds, nuts, leaves, bark, seedlings

what are key characteristics of sorghum species/millet?

• large seed head

• slender leaves

what makes sorghum species/millet toxic?

can contain toxic levels of cyanide and nitrates

what are key characteristics of johnsongrass?

• coarse perennial grass

• height up to 8ft

• large, open seed head

• often has brown blotch on leaves

why is johnsongrass toxic?

can contain toxic levels of cyanide, nitrates, & hordenine (alkaloid)

what are the 2 types of photosensitivity? how do they occur and how do they manifest?

1. primary: sensitize the skin through contact or ingestion (unpigmented skin most affected) → sunburn, swelling, ulcers, blindness

2. secondary: toxins damage liver → prevents phylloerythrin

what is photosensitization? what plant causes this reaction?

• when the animal becomes sensitive to sunlight

• st. john’s wort

what should be done with an animal exhibiting photosensitivity?

• get animal to the shade

• topical treatment based on severity

• pain management

what is the main clinical sign cicutoxins cause? why are they so dangerous?

• severe convulsant

• causes death by respiratory paralysis resulting from disruption of the central nervous system

what are key characteristics to identify water hemlock?

• carrot family (carrot like odor)

• white flowers in umbrella clusters

• narrow, serrated leaves

• stem has hollow core

how toxic is water hemlock to horses?

very → 8oz could kill a horse

what are nicotinic receptor clinical signs?

• irritate GI tract

  • nausea, colic, diarrhea

• act on the CNS

  • muscle weakness

  • blindness

  • convulsions

  • death

what are the key characteristics to identify yew?

• dark evergreen shrub

• flat needle leaves

• red cupped berry

what are the clinical signs of yew poisoning?

cardiac → bradycardia, acute cardiac failure

what are the key characteristics to identify posion hemlock?

• very tall

• in carrot family → look & smells like carrots

• broad flowering head with many clusters of small white flowers

• purple blotches on stem (definitive ID)

what plant is poison hemlock often confused with?

carrot

how toxic is poison hemlock to horses?

very, 4-5lbs is lethal

what are the key characteristics to identify jimsonweed?

• spikey leaves

• spikey seed pod

“red as a beet, dry as a bone, blind as a bat, mad as a hatter,” refers to the clinical signs of what toxic plant? what causes these signs? explain.

• jimsonweed

• dilated pupils → cannot see

• tachycardia → redness

• muscle twitching, restlessness → erratic movements

• toxin is hallucinogenic at high doses → crazy, seeing things

what plant is hallucinogenic at high doses?

jimsonweed

what clinical signs are seen with atropine toxicity? why?

tachycardia → atropine is used in medicine to raise a slow heartrate

what is the key characteristic to identify nightshades?

• purple flowers with yellow center

• small green fruit turning to shiny red or black

what toxic plant has tiny tomato-like fruit that is non-toxic when mature, but toxic when green?

nightshade

what are the clinical signs of nightshade poisoning?

• NS: weakness, coma, resp paralysis, death

• disruption of parasympathetic NS to regulate involuntary activity

how can ketones become toxic? what issues do they cause in the body?

when they’re produced too quickly they build up in the blood → makes the blood acidic

what is the key characteristic(s) to identify white snakeroot?

• oval leaves, finely toothed, pointed

• grows 3-5ft tall

• small, white flowers in late summer

what is milk fever?

hypocalcemia → blood calcium levels are depleted faster than they’re being replenished

how is white snakeroot excreted?

in the milk of lactating animals

what are clinical signs of white snakeroot ingestion in horses? other species?

• horses → partial throat paralysis, CHF (congestive heart failure)

• other species → muscle trembling, progressive weakness, death, acetone breathe due to ketosis

what are mycotoxins?

produces by fungi infecting the plant

is it safe to feed animals moldy hay? explain why or why not?

no because they often have mycotoxins that can cause serious health issues in animals

what toxin does the mold in sweet clover produce? why is it an issue?

dicumarol → because it is an anticoagulant

the fungus that grows on moldy sweet clover produces what condition physiologically?

impair blood clotting

what are the clinical signs and treatment for moldy sweet clover ingestion?

• petechia and bleeding

• treated with vitamin K

what is black patch disease?

key characteristic of moldy red clover → mold causes brown spots on red clover leaves

what toxin does moldy red clover produce? which fungus produces it?

slaframine → produced by rhizoctonia

what are the clinical signs and treatment of black patch disease?

• “slobbers” in horses

• abortion & infertility

• treated by removing infected hay

what is ergot and where do you find it?

ergot = fungus → can be found on fescue grass seed

explain why horse owners often do not want fescue in their hay?

anorexia + difficult pregnancies

what conditions in cattle are caused by ergot?

• fescue foot

• fat necrosis

• abortion/dystocia

what is fescue foot?

disease on cattle where they have restricted blood flow in their feet due to vasoconstriction

what are the preferred treatments for ergot?

• changing pastures

• removing infected hay

what is thiamin, and why is it important in the body?

• thiamin → vitamin (vitamin B1)

• serves as a coenzyme necessary for metabolizing carbs, fats, and proteins

what is thiaminase, and what happens when it is ingested?

• an enzyme found in few plants and & raw flesh/viscera of some fish and shellfish

• it metabolizes/breaks down thiamine into pyrimidine and thiazole. this makes thiamin levels drop and animals have a thiamin deficiency

what plants produce thiaminase?

1. bracken fern

2. horsetail

what is the key characteristic(s) to identify bracken fern?

• leaf stems straw colored to light brown

• leaf blades broadly triangular in outline

• leaves are pinnately divided 2-3 times and angle back so that they’re parallel with the ground

what is the key characteristic(s) to identify horsetail?

• hollow jointed stems, 2-4 inches tall

• no flowers, scaled “cone” at tip

• grows in wet soils → ditch banks

what is the key characteristic(s) to identify black walnut?

• green fruit with dark staining pigment

• high value wood

what species is affected by the black walnut tree? what are the clinical signs? how is it treated?

• horses

• laminitis

• treated by removing bedding and supportive care w/ IV fluids and pain management

what are cyanobacteria, and what do they create?

• cyanobacteria → bacteria, also called blue-green algae

• produce multiple secondary metabolites like microcystin & anatoxin

what is the key characteristic(s) to identify blue-green algae?

• blue-green or red-brown

• mats, foam, or scum on water

how do cyanobacteria affect pasture animals?

• shock → weakness, pale gums

• GI: V/D, liver failure

• respiratory: difficulty breathing, respiratory arrest

• CNS: ataxia, tremors, muscle rigidity, seizures

• sudden death

what plant causes mechanical irritation to the GI tract when its seed pods are ingested?

cocklebur

what is the key characteristic(s) to identify cocklebur?

seed pod hooks (like velcro)

what is the toxin found in marijuana? what clinical signs are seen with marijuana ingestion?

• toxin → delta-9-tetrahydrocannabinol

• clinical signs

  • sedation

  • ataxia, stupor, light euphoria

how should pastures be managed to avoid toxicities?

• survey pastures & identify toxic weeds

• evaluate/re-evaluate effectiveness of management plan

• change methods or timing if necessary

• vary techniques to minimize costs