Toxicity

Ryegrass is a popular forage choice worldwide, and is a nutritious source of protein and energy for horses and other grazing animals. Although both species of ryegrass are good sources of nutrition and are not toxic in and of themselves,...

Atypical Myopathy (AM) and Seasonal Pasture Myopathy (SPM) are highly fatal muscle disorders in horses caused by the ingestion of seeds of the box elder or sycamore trees. Seeds of these species contain a compound called hypoglycin A that converts...

Monensin is a type of antibiotic commonly found in livestock and poultry feed that is highly toxic to horses. Monensin belongs to a medication class called ionophore antibiotics. These antibiotics are frequently used in feed as parasite control and to...

Anthrax is a rapidly fatal disease caused by the bacterium Bacillus anthracis. This bacterium can infect horses, other livestock species, and humans. Anthrax cases occur globally every year, including sporadic outbreaks in North America. B. anthracis primarily exists as spores...

In recent years, extensive and persistent wildfires have been a growing concern for horse operations everywhere. Evacuation and preventive protocols are often challenging and put a great deal of strain on livestock and their human caretakers. Equally as concerning is...

Selenium (Se) is a micronutrient that horses require in trace amounts to support cellular function. The selenium content in soil contributes to its final concentration in plants. Worldwide, selenium levels in soil vary widely. Selenium imbalances are common in horses....

Pyrrolizidine alkaloids (PAs) are a naturally occurring type of compound found in many species of plants. When ingested, PAs are toxic to horses. Some of the most common plants that contain high concentrations of PAs include Ragwort (Senecio spp.), Rattlepod,...

Blister beetles, also known as oil beetles, secrete a blistering agent called cantharidin as a natural defense against predators. Beetles in this family feed on flower blossoms, particularly in alfalfa plants, which makes them a common contaminant in alfalfa hay....

Alsike clover toxicosis is a potentially life-threatening condition in horses caused by ingesting large quantities of the Trifolium hybridum plant, commonly referred to as Alsike clover. To date, neither the precise mechanism of action nor the specific toxin from Alsike...

Poisonous snake bites (snake envenomation) in horses, while not common, are a medical emergency. Without prompt veterinary attention, snake envenomation can result in severe injury and, in some cases, death. In North America, venomous snakes belong to either the Elapid...

Buttercup poisoning in horses occurs when they ingest protoanemonin, a toxin produced by the buttercup plant. Although relatively rare, the ingestion of this flowering weed results in irritation to the horse’s mouth and digestive tract.

Ionophore toxicosis, a severe and often fatal condition in horses, arises from the ingestion of ionophores, antibiotic compounds that are common in livestock feeds. Common ionophores in livestock feeds include monensin, lasalocid and salinomycin. These antibiotics increase growth rates in...

Fescue toxicosis in horses results from ingestion of fescue grass contaminated with the fungus Neotyphodium coenophialum. The fungus produces ergot alkaloid toxins which cause changes in hormone concentrations and blood flow in pregnant mares grazing contaminated pastures or hay. Nearly...

Slobbers, otherwise known as slaframine poisoning or salivary syndrome, is a condition that causes excessive salivation or drooling in horses. It is relatively rare and usually occurs in outbreaks, with multiple horses affected at once. Slaframine intoxication is caused by...

Black walnut tree poisoning occurs when horses come into contact with toxic compounds in the black walnut (Juglans nigra) tree. The roots, bark, wood, nuts, pollen and leaves of the tree contain a chemical that is poisonous to horses upon...