Common Milkweed

Latin Name: Asclepias syriaca

Identifying Characteristics:

  • Has sticky milky sap
  • Oval leaves, 4-9 inches long
  • Leaves have very fine hairs on bottom side
  • Flowers are arranged in an umbel with colors including pink, purple, orange, and white
  • Generally, 3 ft tall or less
  • Alternating veins coming off of leaf midrib
  • Underground rhizomes (horizontal stems)

Plant Longevity:

  • Perennial

Where Commonly Found:

  • Fence rows
  • Roadsides
  • Fields
  • Prairies
  • Pastures
  • Pollinator plantings

Time of Most Concern:

  • When plant is green or dried in hay

Compound that Causes Concern:

  • Galitoxin found in the sap
  • Several glycosides
    • Western species of milkweed, namely labrifom, whorled, and broadleaf milkweed, have higher concentrations of cardiac glycosides, whereas common milkweed lacks significant amounts of toxic cardiac glycosides
  • Alkaloids

Part of Plant Most Toxic:

  • Stems
  • Leaves
  • Roots

Livestock Species Affected:

  • Cattle
  • Goats
  • Sheep
  • Horses
  • Poultry

Pasture, Stored Feed, Both:

  • Both

Clinical Signs:

  • Irregular pulse
  • Vomiting
  • Diarrhea
  • Trouble breathing
  • Loss of coordination

Amount Needed to be Consumed for Clinical Signs / Death:

  • Studies have found that cattle can graze low amounts of milkweed with no effect, reducing need to strict control of this important plant to native pollinators.
  • Toxic dose almost same as lethal dose
    • As little as 2% of animal's body weight
    • That would equate to 20 lbs in a 1,000 lb cow
  • Frost decreases toxicity

Identifying Characteristics:

  • Has sticky milky sap
  • Oval leaves, 4-9 inches long
  • Leaves have very fine hairs on bottom side
  • Flowers are arranged in an umbel with colors including pink, purple, orange, and white
  • Generally, 3 ft tall or less
  • Alternating veins coming off of leaf midrib
  • Underground rhizomes (horizontal stems)

Plant Longevity:

  • Perennial

Where Commonly Found:

  • Fence rows
  • Roadsides
  • Fields
  • Prairies
  • Pastures
  • Pollinator plantings

Time of Most Concern:

  • When plant is green or dried in hay

Compound that Causes Concern:

  • Galitoxin found in the sap
  • Several glycosides
    • Western species of milkweed, namely labrifom, whorled, and broadleaf milkweed, have higher concentrations of cardiac glycosides, whereas common milkweed lacks significant amounts of toxic cardiac glycosides
  • Alkaloids

Part of Plant Most Toxic:

  • Stems
  • Leaves
  • Roots

Livestock Species Affected:

  • Cattle
  • Goats
  • Sheep
  • Horses
  • Poultry

Pasture, Stored Feed, Both:

  • Both

Clinical Signs:

  • Irregular pulse
  • Vomiting
  • Diarrhea
  • Trouble breathing
  • Loss of coordination

Amount Needed to be Consumed for Clinical Signs / Death:

  • Studies have found that cattle can graze low amounts of milkweed with no effect, reducing need to strict control of this important plant to native pollinators.
  • Toxic dose almost same as lethal dose
    • As little as 2% of animal's body weight
    • That would equate to 20 lbs in a 1,000 lb cow
  • Frost decreases toxicity

https://plants.usda.gov/DocumentLibrary/plantguide/pdf/cs_assy.pdf

https://hort.extension.wisc.edu/articles/milkweed-ornamental-plants-toxic-to-animals/

Dickson et al. Cattle graze central US milkweeds at least as much as grasses, even under patch-burn-grazing management. Rangeland Ecology and Management. 2023