Magnesium Solubility in the caecum in response to pH changes
D.E. Dalley, P. Isherwood, A.R. Sykes, A.B. Robson
Animal and Veterinary Sciences Group, Lincoln University,
Canterbury, New Zealand
Proceedings of the New Zealand Society of Animal Production.
1992, 52: 103-106
Five two-tooth Coopworth ewes were used to monitor the effects
of changing caecal pH on magnesium (Mg) solubility and absorption pH
change was induced by infusion of volatile fatty acid (VFA) (0, 220,
440, 660, 880 mmol; ration 0.80:0.15:0.05 acetic:propionic:butyric in
2016 ml of deionised water) into the terminal ileum for 24 h.
Treatments were randomly applied to each animal using a latin square
design. During the infusion samples of blood and urine were taken at 4
h intervals and proximal colonic digesta at 4, 16 and 24 h. Apparent Mg
absorption from the large intestine was estimated from changes in plasma
Mg concentration and urinary Mg excretion. Sixteen hours after the
commencement of infusion digesta pH decreased and Mg solubility
increased. For example, with the 880 mmol infusion digesta pH had
decreased by 2.1 ± 0.48 units and Mg solubility increased from 21 ± 2.6
to 52 ± 1.2%. Increasing VFA infusion tended to decrease plasma Mg
concentration. Urinary Mg excretion (mg/h) increased during the first 4
h of infusion on all treatments but this increase was not sustained so
that by 24 h urinary excretion was at or below levels prior to infusion.
Results indicate that Mg solubility in caecal and proximal colonic
digesta is responsive to changes in pH. The lack of response of Mg
absorption was surprising and possible reasons are discussed.
Keywords: NZSAPAB;
Absorption; large intestine; magnesium; solubility; pH; volatile
fatty acids, sheep.
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Last Updated 25-01-1997
