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Acorn Calves
AG Morton, District Veterinarian, Wagga Wagga
Acorn calves have been sporadically recorded on the South West Slopes since 1957 when Max Barry, Veterinary Inspector Albury/Hume reported the condition.
The name 'acorn calves' was derived from the USA where some early investigators thought the condition was caused by pregnant cows eating acorns. This theory was subsequently disproved however the name has stuck.
Farmers report the calves as looking like bull dogs or bull terriers, premature closing of the growth plates causing bones to be shortened.
The first cases in our 1991 outbreak were seen in late April 1991 and continued until September 1991.
A puzzling feature of the outbreak was the enormous variation in the pattern of outbreaks. On some properties 100% of calves were affected, on others as few as one calf was affected. On some properties the outbreak was of short duration with all calves normal then a few calves affected over a few days and then all calves normal. On other properties the outbreak was extended with a sprinkling of cases throughout calving. Sometimes only one mob was affected, in other cases all mobs were affected. Farms in close proximity varied greatly in both the level and pattern of outbreaks.
Outbreaks did not appear to correlate with soil types, supplementary feeding, breed or age.
A wide range of specimens were tested for viruses, e.g. Akabane, without any positive results. Pre-suckling blood samples were checked for immunoglobulins and generally indicated that an infectious agent could not be incriminated. Routine biochemistry was unrewarding.
Liver manganese levels appeared to be deficient on some but not all properties. There were some difficulties in interpreting results as:
(1) 'normal values' vary in the literature
(2) we do not know at which stage of pregnancy the bony changes occur.
In Canada acorn calves have been produced experimentally by feeding cows mouldy barley straw. In New Zealand feeding cows a manganese deficient diet of apple pulp and corn silage has produced acorn calves.
The manganese deficiency story is very confusing as a soil chemist at the A.R.I told me that while some of the areas experiencing acorn calves might have low manganese levels other would be expected to have high levels.
Some farmers tried supplementing with manganese sulphate (which is relatively cheap at $2.50kg) however it is extremely impalatable.
John Glastonbury, Officer in Charge, RVL Wagga Wagga is of the opinion that pathologically the condition is most likely to be a deficiency or toxin. This seems to be hard to accept given the extraordinary diversity of soil types and areas that the condition was (and has been) reported from.
Wise old Vets point to the pattern of outbreaks are more likely to be infectious in origin and certainly the patterns of outbreaks mimic incidents like Akabane.
Farmers frequently comment that the problem often occurs when cows have had a hard time (or drought) during pregnancy and that hard time has followed a very wet year.
Regrettably an epidemiological survey of affected properties which was to be undertaken by NSW Agriculture was not completed and so we await the next outbreak in blissful ignorance!