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Abstract
Between January 1987 and June 1988, when cattle were in mid-late lactation and not receiving supplementary magnesium, pasture samples were taken for magnesium, sodium, and potassium analysis from 134 dairy properties in Taranaki and the Waikato, and a composite serum sample from ten cows in each herd for magnesium analysis. Urine from the same herds was analysed for sodium, and for 31 herds in 1988 for magnesium.
A severe cyclonic disturbance in early 1988, Cyclone Bola, was associated with changes in pasture sodium, potassium and magnesium, urinary sodium, and serum magnesium concentrations.
In 1987, before the occurrence of Cyclone Bola, the Taranaki pastures had higher pasture sodium and lower potassium concentrations, and the Taranaki cattle had higher urinary sodium concentrations. In 1988, after Cyclone Bola, pasture sodium concentrations were higher in both Taranaki and the Waikato, and pasture magnesium concentrations higher in Taranaki than the Waikato.
The high pasture sodium concentrations throughout Taranaki appeared to arise from strong prevailing winds bearing sea spray. The geological features of this region create wind turbulence which is responsible for the salt being deposited long distances inland.