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Studies on magnesium in ruminant nutrition

11.* Effect of lactation on the excretion of calcium and potassium by grazing monozygotic twin cows

Published online by Cambridge University Press:  09 March 2007

A. C. Field
A. C. Field
Affiliation:
Moredun Research Institute, Gilmerton, Edinburgh 9
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Abstract

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1. The excretion of calcium and potassium in urine, milk and faeces by grazing monozygotic twin cows has been determined at intervals throughout four grazing seasons.

2. In Expt I three sets of twins were used to study the variation within pairs in the excretion of Ca and K. It was found that the variation within pairs was non-significant and small, less than 5% of the overall mean, for all but one of the factors measured. The variation in urinary excretion of Ca within pairs was significant (P <0.05) in 1962.

3. In Expt 2 the effects of lactation on the excretion of Ca and K by three sets of twins were studied over two grazing seasons. Only one of each of the twins was in milk at a time, each twin being in milk for one season.

4. Lactation increased (P <0001) urinary and faecal Ca in 1964 but not in 1965. The concentrations of Cain the faeceswere lower (P <0.01) for lactatingthanfornon-lactating cows.

5. Lactation increased (P < 0.001) the excretion of K in urine and faeces. Differences within pairs in faecal concentration were significant in 1964 (P <0001) and 1965 (P < 0.01), but the effect was not attributable to lactation.

6. Significant differences between pairs were found for urinary Ca and K in 1964 (P < 0.05) and for the concentration of K in faeces in both years ( P < 001 or P < 0.001).

7. In 1964 greatest total excretions of Ca were found in June and July and of K in May, whereas in 1965, although the differences between periods for Ca and K were significant (P < 0.001), there were no obvious seasonal trends.

8. Mean intakes of Ca and K by the cows have been calculated from the estimated drymatter intake of herbage and the Ca and K content of the cut herbage and compared with total excretion in urine, milk and faeces. The differences between intake and excretion differed between periods (P < 0.001); for Ca, negative values were greatest in July and August in 1964 but not in 1965 and for K the values were small in July and large and positive in May, September and October in both years. The differences between lactating and non-lactating cows were significant for Ca(P < 0.001) and K (P < 0.01) in 1964. Selective grazing was considered to be the main factor responsible for these differences.

Type
Research Article
Information
British Journal of Nutrition , Volume 24 , Issue 1 , March 1970 , pp. 85 - 96
Copyright
Copyright © The Nutrition Society 1970

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