20 be obvious external signs or clues. Toxic and metabolic processes are unlikely to produce
asymmetric deficits. • hypocalcaemia or hypomagnesaemia
• meningitis as extension of bacterial pneumonia, i.e. thrombotic meningoencephalitis • tick fever, especially Babesia bovis
• grain poisoning can cause staggering and blindness • poisoning with lubricants, fumigants or exhaust gases
• polioencephalomalacia from dietary changes
2.10.1 Hypocalcaemia and hypomagnesaemia
In shipboard cattle this is most likely to occur in association with sudden climatic or dietary changes or after long periods of food and water deprivation while being transported or held
in yards. Hypocalcaemia and hypomagnesaemia usually accompany each other to varying degrees and clinical signs will be related to which is more profound. Rumen acidosis from
feeding batches of pellets with higher than normal levels of fermentable carbohydrates is consistently accompanied by hypocalcaemia.
Hypocalcaemic cattle may be seen to be ataxic before becoming recumbent and depressed with a dry nose and reduced rumen movements. Simple hypocalcaemia is diagnosed if
treatment with subcutaneous calcium injections leads to an immediate and complete recovery. Hypocalcaemia complicated by indigestion will require other treatments to
normalize rumen function such as feeding hay, lowering pH with sodium bicarbonate or administration of rumen fluid from a healthy animal. With hypomagnesaemia, an affected
animal usually exhibits hyperexcitability, convulsions, falling on its side with its legs alternately extended and relaxed. Death may occur during the convulsions. Frothing at the
mouth and profuse salivation are evident. If either disease is suspected, treat with subcutaneous administration of commercially available solutions that contain both calcium
and magnesium.
2.10.2 Meningitis
Meningitis is usually an extension of bacterial pneumonia, most commonly Histophilus somni formerly Haemophilus somnus , but possibly Listeria monocytogenes. Histophilus somni
can cause an acute, often fatal, septicaemic disease that can involve the respiratory, cardiovascular, musculoskeletal, or nervous systems, either singly or together. Affected
cattle are usually found dead but may display premonitory nervous signs from thrombotic meningoencephalitis associated with septicaemic episodes.
2.10.3 Tick fever
Of the three organisms, Babesia bovis, Babesia bigemina and Anaplasma marginale, that cause tick fever in Australia, Babesia bovis is responsible for about 80 of outbreaks.
Babesia bovis may manifest as nervous signs if parasitised red blood cells block capillaries in the brain. Shipboard cattle may be affected by tick fever if they were incubating the
disease during transport and loading. Cattle must have had exposure to cattle ticks in the previous one to four weeks. Clinical signs of tick fever caused by the two babesias include
fever, anaemia, jaundice and red urine and deaths usually occur. With anaplasmosis there is mild fever, anaemia and jaundice but no red urine and deaths are rare. Early treatment with
imidocarb usually results in a rapid recovery; treatment with tetracycline antibiotics may
21 reduce severity of symptoms if imidocarb is unavailable. Vaccines are available to assist
prevention.
2.10.4 Grain poisoning
If severe, grain poisoning can cause staggering and blindness, probably related to hypocalcaemia and haemoconcentration. The exact pathophysiologic basis of the blindness
is unknown.
2.10.5 Poisoning with lubricants, fumigants or exhaust gases.
Lubricants and fumigants will likely have contaminated feed; exhaust gases should be suspected if there is proximity to a combustion engine.
2.10.6 Polioencephalomalacia
Polioencephalomalacia from dietary changes resulting in reduced thiamine or high sulfur intake can cause listlessness, incoordination, ataxia, progressive blindness, head pressing
and opisthotonus. The condition may occur in individuals or as an outbreak. Differential diagnoses for cattle include lead poisoning, water deprivation, salt poisoning, Histophilus
meningoencephalitis, coccidiosis with nervous involvement, and vitamin A deficiency.
Treatment, if given early, with injections of thiamine usually results in rapid improvement and eventual recovery. Non-steroidal anti-inflammatory drugs may assist. Gradual dietary
changes may prevent occurrence.
2.11 Prolonged recumbency
