Camelidae and Cervidae Poisonous Plants – NAVLE Study Guide

Overview and Clinical Importance

Plant poisoning represents a significant cause of morbidity and mortality in South American camelids (llamas and alpacas) and cervids (deer, elk, moose). Unlike domestic ruminants, camelids are modified ruminants with a three-compartment stomach and unique browsing behaviors that predispose them to toxic plant ingestion. Cervids demonstrate remarkable natural tolerance to certain toxins but remain susceptible to others. Understanding species-specific sensitivities, clinical presentations, and treatment protocols is essential for NAVLE success.

Camelids are browsers by nature, seeking nutrients from leaves, twigs, and bark in addition to pasture grasses. This behavior, combined with their high mineral requirements, can lead them to consume dangerous plants. Many poisonous plants are not native to the Andean highlands where camelids evolved, meaning they lack innate avoidance behaviors for common ornamental and garden plants.

Cardiac Glycoside-Containing Plants

Oleander (Nerium oleander)

Oleander is one of the most lethal plants for camelids. A single leaf can be fatal to an adult alpaca. The plant contains cardiac glycosides (oleandrin, neriine) that inhibit the Na+/K+-ATPase pump, leading to increased intracellular calcium and disrupted cardiac conduction.

Clinical Presentation and Management

Foxglove (Digitalis purpurea)

Foxglove contains digoxin and digitoxin, the prototype cardiac glycosides. All parts of the plant are toxic, and toxicity persists after drying. Clinical presentation is similar to oleander, with GI signs typically preceding cardiac manifestations by several hours.

Yew (Taxus species)

Yew contains taxine alkaloids (taxine A and B) that inhibit sodium and calcium channels in cardiac tissue, causing fatal arrhythmias. All parts except the fleshy red aril are toxic. Toxicity is NOT reduced by drying.

Species Differences: This is a HIGH-YIELD NAVLE concept. Wild deer, moose, and elk browse on yews as winter food and are NOT affected by yew toxins. This remarkable tolerance is unique to cervids. In contrast, horses and cattle can die within 15 minutes of consuming yew leaves. As little as 0.1-0.5% of body weight in yew leaves is lethal to cattle.

Grayanotoxin-Containing Plants (Ericaceae Family)

Rhododendron and Azalea (Rhododendron species)

Rhododendron poisoning is a common veterinary emergency in small ruminants and has been documented in camelids. The plants contain grayanotoxins (andromedotoxins) that bind to voltage-gated sodium channels, causing permanent hyperpolarization of excitable cells including neurons, myocytes, and cardiomyocytes.

Lethal dose: As little as 0.2-0.6% of body weight can be fatal. Rhododendron is NOT native to the Andean habitat of camelids, so they lack evolved avoidance behaviors.

Clinical Signs of Rhododendron Poisoning in Camelids

Treatment Protocol for Rhododendron Toxicosis

• Decontamination: Activated charcoal (100-200 g) and magnesium oxide (10-20 g) orally - AVOID in animals with uncoordinated regurgitation due to aspiration risk
• Fluid therapy: Parenteral rehydration with isotonic crystalloids
• Metabolic acidosis: Sodium bicarbonate infusion
• Cardiac arrhythmias: Atropine for bradycardia
• Lipid emulsion therapy: IV lipid emulsion may be beneficial (grayanotoxins are lipophilic)
• Antibiotics: Prophylactic antibiotics if aspiration pneumonia risk

Oak and Acorn Toxicosis (Quercus species)

Oak toxicosis has been documented in camelids, with the first reported case in South American camelids involving two adult llamas that developed acute renal failure after exposure to oak trees. The toxic principles are tannins (gallotannins) that are hydrolyzed in the rumen to gallic acid and pyrogallol, which are nephrotoxic and hepatotoxic.

Species Susceptibility to Oak Toxicosis

Cervids (deer) have evolved tannin-binding salivary proteins that neutralize the toxic effects of tannins. This allows them to consume acorns as a dietary staple, especially during fall and winter. Cattle, sheep, horses, and camelids LACK these protective salivary proteins and are susceptible to toxicosis.

Treatment of Oak Toxicosis

• Polyethylene glycol (1 g/kg/day): Binds tannins and reduces tissue damage
• Calcium hydroxide supplementation: 10% in pelleted ration (1 kg/head/day) as preventive
• Activated charcoal: Early administration may reduce absorption
• Aggressive IV fluid therapy: To support renal function and correct dehydration
• Prognosis: Poor once severe renal dysfunction is established; recovery may take 60+ days if animal survives

Pyrrolizidine Alkaloid-Containing Plants

Pyrrolizidine alkaloids (PAs) cause chronic, irreversible hepatotoxicity with a delayed onset. Common sources include ragwort (Senecio jacobaea), groundsel (Senecio species), and various plants in the Boraginaceae family. PAs are metabolized by hepatic cytochrome P450 to reactive pyrrole metabolites that damage DNA and hepatocytes.

Common PA-Containing Plants

Clinical Presentation of PA Toxicosis

KEY CONCEPT: Signs may appear weeks to months after plant ingestion, making diagnosis challenging. The liver has limited regenerative capacity after PA damage.

• Weight loss and poor body condition
• Photosensitization (secondary to hepatic failure)
• Icterus/jaundice
• Hepatic encephalopathy (dullness, circling, head-pressing, blindness)
• Ventral edema (hypoalbuminemia)
• Diarrhea

Diagnosis and Treatment

• Liver enzymes: GGT, GDH may be elevated; serum bilirubin increased
• Hepatic biopsy: Megalocytosis (enlarged hepatocytes) is pathognomonic
• Pyrrole-protein adducts: Can be detected in blood samples
• Treatment: Supportive care only; remove from toxic pasture; high-carbohydrate, low-protein diet; prognosis is GUARDED to POOR

Comprehensive Summary: Major Toxic Plants