Production Animal Clinical Toxicology

Plants | Epidemiology | Pathogenesis | Clinical Signs | Clinical Pathology | Necropsy | Diagnosis | Treatment

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Plants

Swainsona spp. (50) - Darling peas (all Australian natives)

Epidemiology

animal factors

• cattle, sheep, horses affected
• cattle more severely affected, although sheep more likely to be affected in larger numbers; horses more rarely affected
• young animals more susceptible
• most property bred stock will avoid it or may develop a tolerance; some animals appear to develop a craving and will actively seek plant despite presence of alternatives

plant/environmental factors

• perennial plants that develop quickly after early spring or autumn rains
• can be predominant species in pasture
• poisoning most likely after drought or if feed shortage

Pathogenesis

• toxin is swainsonine, an indolizidine alkaloid
• alkaloid inhibits lysosomal alpha-mannosidase which leads to accumulation of mannose-rich oligosaccharides in vacuoles in variety of cells including those of the nervous system
• results in cellular dysfunction
• is an induced mannosidosis, a lysosomal storage disease similar to the genetic mannosidosis.

Clinical Signs

• signs may develop after 3-4 weeks grazing
• loss of condition
• development of neurological symptoms
• staring eyes, agonised expression
• unusual head carriage
• high in sheep
• low in cattle/horses
• stiff gait and incoordination
• frequent trembling of head and limbs
• hyperexcitability especially in cattle and horses
• neurological signs may progress; may intensify with stress
• collapse and death
• some sheep may have only a progressive non-reversible loss of condition without nervous signs
• cattle will have poor breeding performance from abortion, stillbirths and increased perinatal mortality.

Clinical Pathology

• nonspecific

Necropsy

• generally nonspecific
• in sheep showing only loss of condition, anterior and mid brain stem may have a symmetrical golden-yellow discolouration
• histopathology shows vacuolation in neurone bodies and in epithelium of various organs including kidney, pancreas, liver, thyroids

Diagnosis

• history of access
• clinical signs, histopathology

Treatment

• most will recover in about 6 weeks following removal from pasture