Case report. An outbreak of locoweed poisoning in horses in Southwestern Alberta.

The research paper focuses on an outbreak of locoweed poisoning in horses in Southwestern Alberta, highlighting the plant’s detrimental impact on various types of range livestock. Locoweed’s toxicity has been a longstanding concern within western North American livestock, with its consumption leading to severe physical and behavioral changes in horses, cattle, and sheep.

Locoweed’s Impact on Range Livestock

• In areas where it grows abundantly, such as rangelands and along the eastern slopes of the Rocky Mountains, locoweeds get consumed by livestock mainly during periods of scarce forage or inadequate salt.
• This plant has a cumulative poisonous effect on livestock, leading to serious health problems that tend to peak after the animals stop ingesting it.
• Interestingly, livestock, particularly horses, develop a habit or craving for the locoweeds and tend to become very selective in their consumption—eating locoweeds almost exclusively.
• The tendency to thrive on this plant typically does not wane even after removing the animals from the weed-infested ranges.

Differences in Susceptibility and Effects in Animals

• The severity of the locoweed’s poison varies depending on the plant species, animal species, and even the specific individual animal.
• Horses are considerably more prone to this plant’s toxicity than cattle or sheep. They consume larger amounts and show quicker onset and progression of the toxic symptoms.
• The first signs of such poisoning in horses are normally depression, abnormal sensitivity to handling, and loss of coordination, followed by emaciation, abnormal locomotion, and significant behavior changes. Ultimately, death ensues.

Characteristical Changes in Livestock

• In both horses and ruminants like cattle, the plant’s poisoning results in extensive microscopic anatomical changes, especially widespread vacuolation and degeneration of neurons in the brain.
• Livestock poisoned by locoweeds develop a peculiar gait and tend to become unaware of their surroundings. They may thus unintentionally find themselves in precarious situations they would generally avoid. For instance, sheep lose their directional sense and flocking instinct.
• The locoweed’s consumption by sheep and cattle during the early stages of gestation causes congenital malformations in the offspring.

Economic Implications and Management

• While mildly poisoned cattle can still achieve market weight via adequate feeding, severely affected cattle will continuously lose weight and eventually die.
• Grave as the effects are, there seems to be no remedy for locoweed poisoning. Mildly affected horses, for example, will retain an irregular gait and can pose a risk to riders.