The clinical differentiation of nervous and muscular locomotor disorders of sheep in Australia

SUMMARY Many of the nervous and muscular locomotor disorders that affect sheep throughout Australia are commonly referred to as ‘staggers’ syndromes. The range of clinical signs displayed by sheep suffering these disorders is sufficiently diverse to enable each syndrome to be graded into one of 5 progressive clinical groups. The first group, the limb paresis syndromes, includes the primary myopathies associated with the ingestion of Ixiolaena brevicompta, Malva parviflora , and Trachymene ochracea , as well as selenium and vitamin E disorders, Paroo virus staggers, congenital progressive muscular dystrophy, humpy back, hypocalcaemic muscle weakness, Tribulus terrestris staggers and tetanus . The second group is characterised by limb paresis with knuckling of the fetlocks, and includes the plant‐associated toxicities of Romulea rosea, Stachys arvensis, Trachyandra divaricata, and Tribulus micrococcus , together with haloxon toxicity, enzootic ataxia (copper deficiency), and the probably genetic disorders of segmental axonopathy, neuroaxonal dystrophy, and degenerative thoracic myelopathy. Other locomotor disorders that fit more loosely into this group are listerial myelitis (post‐dipping staggers), vitamin A deficiency, cervico‐thoracic vertebral subluxation, Stypandra glauca toxicity, Ipomoea spp toxicity, ivermectin toxicity, and botulism . The third group, the falling syndromes, includes the probably genetic disorders of thalamic cerebellar neuropathy, cerebellar abiotrophy, and globoid cell leucodystrophy, together with Swainsona spp toxicity . The fourth group, the falling‐with‐tremors syndromes, includes the plant‐associated toxicities of phalaris staggers, perennial rye grass staggers and nervous ergotism ( Claviceps paspali ) . The fifth group, the convulsive syndromes, includes the polioencephalomalacic entity nardoo fern ( Marsilea drummondii ) staggers, outbreaks of focal symmetrical encephalomalacia and the tunicaminyluracil toxicities known as annual ryegrass ( Lolium rigidum ) toxicity, annual beard grass ( Polypogon monspeliensis ) toxicity, blow away grass ( Agrostis avenaceae ) toxicity, and water damaged wheat ( Triticum aestivum ) toxicity . A dichotomous system is presented for the differential diagnosis of these groups of conditions .