The effect of Ruapehu ash on the trace element status of grazing ruminants in the Taihape District

Abstract

Aims. To investigate the impact of a large (2–5 mm) volcanic ash deposition containing sulphur and selenium on the trace element status of livestock grazing affected farmland.

Methods. The trace element status of lambs, cows and hinds were compared on affected properties from slaughterhouse liver samples taken prior to and following the eruption at corresponding times of the year. Liver concentrations of selenium, copper and vitamin B₁₂ were compared.

Results. There was a statistically significant elevation of liver selenium concentration in all classes of stock sampled. Contrary to expectations, liver copper concentrations did not fall in any class of stock sampled and in fact with hinds there was a statistically significant elevation. The Vitamin B₁₂ status of lambs showed a significant reduction, which could not be attributed to any specific aspect of the composition of the ash.

Conclusions. A large deposition of selenium in volcanic ash which increased pasture levels by a factor of about 10 times also increased the liver selenium concentration of livestock. A large deposition of sulphur in volcanic ash which increased soil sulphur levels by a factor of about 30 times on a yellow brown loam soil did not result in a depletion of the liver copper concentrations of livestock grazing the affected farmland.

Clinical relevance. Ruapehu ash deposits increased the liver selenium concentrations of livestock but did not result in toxic levels. Large ash deposits of sulphur to the yellow brown loam soil increased soil sulphur concentrations to many times that which could be achieved economically with fertiliser but did not result in liver copper depletion of livestock.

KEY WORDS:

• Volcanic ash
• trace elements
• livestock