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PARESIS may be defined as 'a deficiency in the generation of the gait or in the ability to support weight' and implies that a degree of voluntary movement is still present. Paralysis (plegia) is the complete loss of voluntary movement. Muscle weakness is associated with both conditions but may also be due to other causes.
History taking
With reference to the chief complaint, it is important to ask the farmer about onset, duration, evolution (static, progressive, waxing and waning, episodic) and lateralisation of clinical signs (unilateral, bilateral, more marked on the right or left). Ascertaining which animals and how many are affected is also important, as are any relevant husbandry factors. Examples include:
[black square] What are the sheep currently being fed? Has the diet changed recently?
[black square] Are there known/suspected mineral/trace element deficiencies on the farm?
[black square] Has the affected animal/group/flock received any treatments recently?
[black square] Is the flock open or closed?
[black square] What is the origin of the affected animals?
Neurological examination
The core objectives of a neurological examination, together with the history, are to determine:
[black square] Whether the condition is neurological;
[black square] What part of the nervous system is affected;
[black square] A list of differential diagnoses for the clinical signs observed;
[black square] An appreciation of the severity of the disease (in order to give a prognosis).
A neurological examination should always be accom-panied by a full clinical examination to avoid missing non-neurological causes of the presenting complaint (eg, orthopaedic), as well as those that manifest in neurological signs secondary to generalised metabolic, infectious, toxic or nutritional disturbances ( Box 1 ).
Box 1: Common causes of recumbency in sheep It is important to determine whether a recumbent sheep is down due to a primary nervous system lesion or is affected by a different problem that may be unrelated to the nervous system or that may affect it indirectly. Examples of commonly encountered causes of recumbency include:
Primary neurological disorders
[black square] Listeriosis (infection of the trigeminal nerve and associated brainstem nuclei by Listeria monocytogenes );
[black square] Spinal cord trauma.
Systemic disturbances that affect the nervous system (secondary neurological disorders)
[black square] Hypocalcaemia (see Video 1 );
[black square] Hypomagnesaemia;
[black square] Polioencephalomalacia...