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MAGNESIUM METABOLISM IN THE RUMENS OF LACTATING DAIRY COWS FED ON SPRING GRASS
Author(s) -
Johnson C. L.,
Helliwell S. H.,
Jones D. A. Aubrey
Publication year - 1988
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0144-8757
DOI - 10.1113/expphysiol.1988.sp003120
Subject(s) - rumen , zoology , chemistry , excretion , urine , metabolism , feces , endocrinology , biology , food science , biochemistry , ecology , fermentation
Six rumen cannulated lactating Jersey cows were used to study the effects of an abrupt change from a dry diet to young spring grass on mineral metabolism in the rumen, on plasma Mg 2+ levels and on water intake. There was an increase in the intake of dietary Mg 2+ and concentration of ultrafilterable Mg 2+ in rumen fluid when the grass was fed associated with a fall in plasma Mg 2+ concentration and percentage urinary Mg 2+ excretion. The pH of rumen fluid fell when the cows were fed grass and there was a close inverse relationship with the concentration of ultrafilterable Mg 2+ and Ca 2+ . Changes occurred in the mineral composition of rumen fluid that interact to affect the absorption of Mg 2+ . The concentrations of NH 3 , ultrafilterable K + and ultrafilterable Ca 2+ increased and the concentration of ultrafilterable Na + decreased. These changes were associated with an increase in the potential difference between rumen fluid and blood (positive). Water consumption fell abruptly when the grass was fed and some cows drank no water on several days. However, total water intake was almost doubled resulting in an increased rumen volume.