Production Animal Clinical Toxicology

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

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Plants

Lolium perenne - perennial rye grass

Lolium rigidum - annual or Wimmera rye grass

Epidemiology

2 distinct syndromes related to plant species

a. perennial rye grass staggers

plant/environmental factors

• usually late summer, autumn
• grass dry and short with little growth
• only in pastures infected with endophytic fungus Acremonium lolii
• only infests intercellularly crown, leaf sheath, floral axis
• most abundant during late summer/autumn
• produces lolitrem B toxin

animal factors

• sheep, cattle, horses affected
• younger classes of stock more affected

b. annual rye grass staggers

plant/environmental factors

• usually late spring, summer
• pasture is mature
• only in pasture co-infested both with nematode Anguina funesta and a bacterium Clavibacter toxicus (formerly Corynebacterium rathayi)
• flowers infested by nematode, seeds replaced by galls, bacterium then dominates galls
• C. toxicus produces a tunicamycin-like toxin

animal factors

• sheep and cattle affected

Pathogenesis

a. perennial rye grass staggers

• lolitrem produces functional derangement, but mechanism uncertain
• recovery in majority of cases once animals removed from source

b. annual rye grass staggers

• toxin thought to affect glycoproteins including some neurotransmitters and fibronectin
• results in vasospastic effects, damaged blood vessels, haemorrhage, cerebral oedema and foci of anoxia
• recovery rare

Clinical Signs

• onset 7-14 days once on toxic pasture
• fine and coarse tremors exacerbated by movement
• especially head, neck, shoulder, flank
• head nodding, jerky limb movements
• limbs move without flexion resulting in stiff, bounding gait
• lateral recumbency, head extended, back arched
• tetanic spasm
• if left undisturbed animals recover, may get up only to repeat clinical signs
• 5-75% affected; mortality rare primarily due to misadventure
• symptoms may only appear on driving
• cattle similar symptoms, but may have more marked hind limb ataxia and convulsion more severe
• horses, reeling drunken gait may proceed to posterior paralysis

b. annual rye grass staggers

• onset 2-7 days once on toxic pasture
• coarse tremors, head nodding
• stiff-legged, jumping or swaying gait
• may collapse into ventral or lateral recumbency
• if ventral, often hindlimbs are in posterior extension
• if lateral, opisthotonus, limb extension, tetanic and clonic convulsions
• may recover but still ataxic
• may further collapse spontaneously or if driven
• animals generally die in lateral recumbency
• convulsions, opisthotonus, nystagmus, dyspnoea, tachycardia
• up to 100% of animals affected; mortality can be high if stock not removed at first signs
• signs can occur both spontaneously or on driving
• cattle similar signs

Clinical Pathology

• nonspecific

Necropsy

a. perennial rye grass staggers

• nonspecific

b. annual rye grass staggers

• perivascular oedema of meninges
• pale enlarged friable liver
• widespread haemorrhages

Diagnosis

• history
• perennial - recovery on removal
• annual - presence of yellow slime on plant

Treatment

• perennial - removal from pasture
• annual - none, although for valuable animals some success with benzodiazepine tranquillisers has been reported
• not practical in field

Control

• pasture and grazing management
• perennial - graze for short periods to reduce intake of heavily infected parts of plant
• annual - graze heavily before development of seed
• reduces gall and seed build up
• destruction of rye grass by burning/herbicides for at least 2 seasons to eliminate nematode