Cattle Deaths While Grazing Canola (Nutrition Update, Volume 9)

Prussic Acid Risk in Canola
Attention to the possibility of prussic acid (hydrogen cyanide) poisoning should be of concern when considering utilizing it as a feed for livestock. A reference in Ensminger’s Feeds and Feeding suggested that Brassica species may accumulate cyanogenic compounds under certain conditions.
To address these concerns, experts from the University of Saskatchewan, Western College of Veterinary Medicine, and Saskatchewan Agriculture and Food convened to review the issue. The conclusions were:
  • Canola does contain cyanogenic glycosides and the biochemical pathway necessary to release prussic acid.
  • However, both components occur at very low levels.
  • The biochemical pathway is inherently inefficient in canola.
  • Together, these factors make it highly unlikely that prussic acid would accumulate to dangerous concentrations.
Conclusion:
While the risk is not zero, the likelihood of prussic acid poisoning from grazing canola stubble is very low.
 
Major Risk: Treated Canola Seed
The real and significant risk associated with grazing canola fields arises from treated seed, not from the plant material itself.
  • Counter (terbufos), a systemic insecticide used to treat canola seed, is highly toxic to mammals, birds, fish, and wildlife.
  • Even small amounts can cause rapid and fatal poisoning in cattle.
Safe Management of Treated Seed
To prevent accidental poisoning:
  • Never dump treated seed in sloughs, low areas, pastures, or fencelines.
  • Do not store treated seed for later use.
  • Dispose of leftover seed using approved methods, such as double planting, to ensure it is safely incorporated into the soil.
  • Inspect fields carefully before grazing canola stubble, checking for:
    • Seed spills at field entrances
    • Overlaps or planter spills
    • Storage or transfer sites
    • Low spots where seed may accumulate due to water flow
 
Key Takeaways for Producers
  • Canola stubble is generally safe for grazing from a prussic acid standpoint; the risk is considered very low.
  • Treated canola seed is highly toxic and represents the primary danger when grazing canola fields.
  • Prevent access to any spilled or discarded treated seed before releasing cattle.
  • If in doubt, walk the field and remove any suspect seed material.