Within herd variability in the mineral status of grazing dairy cows in
early lactation.
D.E. Dalley
Dairying Research Corporation, Private Bag 3123, Hamilton, New
Zealand.
Proceedings of the New Zealand Society of Animal Production 1994,
54: 27-30
Two groups of 10 mature, crossbred cows received either a single
daily dose of 10 g Mg or no supplemental Mg for two 5 day periods. Blood
was sampled twice daily and urine once daily. On 3 days blood and urine
were sampled four times. Serum Mg levels of 3 unsupplemented animals fell
from 0.74 ± 0.034 to 0.25 ± 0.020 mmol/1 within 5 days while other animals
within this group maintained serum Mg levels despite the absence of Mg
supplementation. At any given sampling time serum Mg levels of individuals
within the unsupplemented group varied from 0.22 to 0.88 mmol/1 and those of
supplemented animals from 0.41 to 0.83 mmol/1. Mean serum Mg, Ca, Na and
K concentrations did not differ between the groups. Unsupplemented animals
had significantly (P<0.001) lower urinary fractional clearance ratios of Mg
and Ca.
The within and between animal variation in serum Mg levels was high for both
Mg supplemented and unsupplemented animals. The fractional clearance of
Mg in urine indicated a likely benefit from Mg supplementation for 100% of
the unsupplemented animals while serum Mg concentrations only identified
40% of these animals. Fractional clearance of Mg in urine has potential as
an indicator of animal Mg status.
Keywords: NZSAPAB;
magnesium; calcium; minerals; dairy cattle; urine; fractional
clearance ratios.
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Last Updated 25-01-1997
