Lupine Toxicity in Sheep: Lupinosis, Liver Injury, and Neurologic Signs

Lupine toxicity in sheep is a broad term for illness linked to Lupinus plants. In practice, vets usually think about two different syndromes. One is lupine poisoning from naturally occurring alkaloids, most often in bitter lupines, which can cause nervous system signs. The other is lupinosis, a liver disease caused when sheep eat lupine plants or stubble infected with the fungus Diaporthe toxica that produces phomopsins.

Lupinosis is the form most strongly associated with liver injury, jaundice, and secondary neurologic signs. When the liver is badly damaged, toxins such as ammonia can build up in the bloodstream and affect the brain. That can lead to stumbling, dullness, disorientation, and eventually recumbency. Some sheep also develop photosensitivity or a painful muscle problem that makes them hunched and reluctant to move.

This condition is most often linked to moldy lupine stems, pods, or crop residue, especially after harvest or during dry periods when forage choices are limited. Severity varies. Some sheep recover with early supportive care, while others decline quickly over several days. Because several toxic and metabolic diseases can look similar in sheep, your vet will need to sort out the cause before advising a treatment plan.

The cause depends on which lupine syndrome is present. Alkaloid lupine poisoning happens when sheep eat lupine species that naturally contain toxic quinolizidine alkaloids, especially so-called bitter lupines. These compounds can affect the nervous system and may cause tremors, weakness, or incoordination.

Lupinosis is different. It develops when sheep eat lupine plants infected with Diaporthe toxica, a fungus previously known as Phomopsis leptostromiformis. The fungal toxins, called phomopsins, damage liver cells and interfere with normal cell division. Over time, that can lead to severe hepatotoxicity, jaundice, poor energy balance, and secondary neurologic signs.

Risk rises when sheep graze moldy lupine stems, pods, or stubble, especially when pasture is short and animals are pushed to eat lower-quality residue. Weather, crop variety, fungal contamination, and how long sheep stay on affected forage all matter. Sheep with significant liver injury may worsen if they are not eating well, and high-protein supplementation may be a concern in some cases because a failing liver may struggle to process ammonia efficiently. Your vet can help tailor feeding changes to the situation.

Diagnosis starts with the history. Your vet will want to know whether the flock recently grazed lupine pasture, harvested lupine fields, or moldy lupine stubble. Timing matters, as does whether multiple sheep are affected. A physical exam may show jaundice, depression, weakness, photosensitivity, or neurologic changes.

Blood work is often the most useful next step. Sheep with lupinosis may have increased liver enzyme activity and higher bilirubin concentrations, which support liver injury. Depending on the case, your vet may also recommend checking hydration, energy status, and other chemistry values to look for complications.

Diagnosis is usually based on a combination of exposure history, compatible signs, and laboratory evidence of liver damage. In some flock situations, your vet may also suggest feed evaluation, necropsy of animals that died, or testing to rule out other causes of jaundice or neurologic disease. Important look-alikes can include copper-associated disease, toxic plants, pregnancy toxemia, polioencephalomalacia, and infectious or metabolic liver disorders.

Prevention starts with pasture and feed awareness. Do not let sheep rely heavily on moldy lupine plants, stems, pods, or stubble, especially when other forage is scarce. Walk fields before turnout, and pay close attention after harvest, drought, weather damage, or visible stem blight. If lupines are part of the forage system in your area, ask your veterinarian or local extension resources about regional risk.

Good flock management also helps. Sheep are more likely to eat risky plant material when they are hungry, crowded, or short on better forage. Offering adequate hay before turnout and rotating away from suspect areas can reduce pressure to consume poor-quality residue. If any sheep begin showing poor appetite, jaundice, or neurologic changes, remove the group from the source right away and contact your vet.

For farms that routinely use lupine forage or residues, prevention may also include cultivar selection, field monitoring, and feed storage practices that reduce fungal contamination. In some settings, oral zinc supplementation has been used under veterinary direction to help reduce liver injury risk from phomopsins, but it is not a substitute for removing contaminated feed. Your vet can help build a practical prevention plan that fits your flock, forage base, and budget.