Production Animal Clinical Toxicology

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

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Plants

• Phalaris aquatica (tuberosa)

Epidemiology

animal factors

• sheep mostly affected, cattle occasionally
• fasted animals may be more susceptible

plant/environmental factors

• phalaris grows best with the onset of rain in autumn and winter
• most toxic pastures are those in rapid growth after a protracted hot dry summer dormancy
• pastures appear more toxic in cloudy, foggy weather or if frost affected
• high plant cobalt levels may protect against the nervous syndrome
• high soil and plant nitrogen levels may predispose to the sudden death syndrome

Pathogenesis

a. sudden death syndrome

• may be several separate entities including a sudden onset polioencephalomalacia, a cardiac syndrome, nitrate toxicity and cyanogenetic glycosides

b. nervous syndrome

• tryptamine and beta carboline indole alkaloids

Clinical Signs

a. sudden death syndrome

• not as common as nervous syndrome and outbreaks not seen concurrently with latter disease
• onset occurs after as little as 12 hr on pasture
• sudden collapse often associated with stress
• laboured respiration
• pounding heart; arrhythmic tachycardia, ventricular fibrillation
• cyanotic mucous membranes
• some affected animals die quickly, others recover

b. nervous syndrome (phalaris staggers)

• more frequent manifestation of phalaris toxicity
• animals need to graze pasture for at least 9 days and it can be up to 11-16 weeks before symptoms develop
• signs can occur some time after removal from pasture
• acute: clinical signs appear for several weeks
• chronic: clinical signs appear for several months
• clinical signs vary in intensity
• hyperexcitability, head nodding
• body tremors, ear twitching
• splaying of digits, limbs may be flaccid or rigid
• ataxia, gait may be proppy or paretic
• fall onto knees, knuckle over at hind fetlocks
• collapse after forced exercise; cardiac respiratory distress after exercise
• sternal recumbency - motionless
• lateral recumbency - struggle to get up
• most affected animals will eventually die

Clinical Pathology

• nonspecific

Necropsy

a. sudden death syndrome

• generalised congestion
• endocardial petechiation

b. nervous syndrome

• green pigmentation of neurones of brain nuclei, and corticomedullary junction of kidney

Diagnosis

• history of access to plants in active growth
• histopathological findings in nervous syndrome

Treatment

• for sudden death syndrome - removal from pasture
• for nervous syndrome - none

Control

• cobalt appears protective for nervous syndrome
• cobalt bullets probably more cost effective than cobalt topdressing
• grazing management