Plants that Contaminate Feed and Forage and Poison Horses: Equine Ttxicology.

Overview

• This research article discusses various toxic plants that, when contaminating feed and forage, can poison horses despite these plants often being unpalatable under normal grazing conditions.
• It identifies key toxic plants responsible for equine poisonings in North America when included in prepared or baled feed, emphasizing how feed contamination and changes in palatability contribute to poisoning incidents.

Introduction to Equine Plant Toxicology

• Many plants that are poisonous to horses tend to be naturally unappealing or avoided when horses have access to ample forage.
• However, when these toxic plants inadvertently mix into prepared or baled feed, the dynamics change, leading to increased risk of ingestion and poisoning.
• Horses in herds may experience competition for feed, which can force them to consume less desirable materials including poisonous plants.
• Additionally, processing of feed such as baling or chopping can increase the palatability of some toxic plants, reducing the natural deterrent effects.

Types of Toxic Plants and Their Effects

• Dehydropyrrolizidine Alkaloid-containing Plants:
  • These plants contain alkaloids known to cause liver damage and chronic poisoning in horses.
  • Examples include common ragwort and other similar species.
• Cocklebur:
  • Contains toxic glycosides that can cause neurological symptoms and gastrointestinal disturbances.
• Salvia reflexa (Western Sage):
  • Contains compounds that may cause poisoning if ingested in significant amounts.
• Saponin-containing Grasses (e.g., Kleingrass, Switchgrass):
  • Saponins are soap-like compounds that can irritate the digestive tract and lead to toxicity.
• Tropane Alkaloid-containing Plants (e.g., Jimsonweed, Black Henbane):
  • These contain alkaloids that affect the nervous system, causing symptoms such as delirium, tachycardia, and colic.
• Lantana:
  • Known to cause photosensitization and liver toxicity in horses.
• Cassia Species and Other Myotoxic Plants:
  • These plants contain toxins that can cause muscle damage and weakness.
• Castor Bean:
  • Contains ricin, a highly potent toxin that can be fatal in small amounts.
• Cyanogenic Glycoside-containing Plants:
  • Release cyanide, which interferes with cellular respiration leading to rapid death if ingested in large quantities.
• Thiaminase-containing Plants:
  • Destroy vitamin B1 (thiamine), leading to neurological problems such as blindness or seizures.
• Hoary Alyssum:
  • Known to cause chronic toxicity with symptoms affecting the digestive tract and general health.

Implications for Horse Owners and Feed Management

• Proper inspection and sorting of feed and forage are crucial to avoid contamination with toxic plants.
• Monitoring plant species in pastures and forage harvest areas can help reduce the risk of contamination.
• Awareness and education about these common toxic plants can prevent accidental poisonings.
• Feed competition and improved palatability after processing can circumvent horses’ natural avoidance of poisonous plants, making vigilance essential.
• Veterinarians and equine toxicologists must consider feed contamination as a potential cause when diagnosing unexplained horse illnesses.

Conclusion

• Equine poisoning by plants is often linked to contamination of prepared feed and forage rather than direct grazing acceptance.
• Understanding the types of toxic plants common in North America and their effects can help improve prevention strategies in horse management.