Indication of intracellular magnesium deficiency in lactating dairy cows revealed by magnesium loading and renal fractional excretion

Abstract

Summary Nine non‐pregnant, lactating dairy cows were used to study plasma and urinary magnesium concentrations ([Mg]pl; [Mg]u), and the urinary fractional excretion of magnesium (FEMg) before, during and after an 120 min intravenous magnesium (Mg) administration (2.5 mg/kg body weight). Animals received a total mixed ration, and Mg content of the diet was within recommended range. Basal mean [Mg]pl, [Mg]u and FEMg were 0.89 ± 0.09 mm, 5.92 ± 2.99 mm and 8.3 ± 9.7% respectively. For all parameters, a substantial inter‐individual variation was observed. Three cows showed suboptimal [Mg]pl and/or [Mg]u as well as low FEMg values of approximately 2% indicating an insufficient Mg supply to these animals (depressed feed intake, reduced absorption of Mg). The applied Mg challenge induced no significant change of mean [Mg]pl in the cows because part of the excess Mg was excreted in the urine. But in five out of nine cows, a decrease of the FEMg, during and after an intravenous Mg load was observed showing that part of the infused Mg is used to replenish intracellular Mg pools. Thus, the existence of an intracellular Mg deficiency in these cows was unmasked by performing the Mg loading test only. Because a reduced free intracellular [Mg] impairs cell and tissue functions, the results highlight the importance of an accurate definition of the intracellular Mg status. The Mg loading test is a suitable procedure, however, for practical purposes less expensive and time consuming methods must be developed.

Invited review: Mineral absorption mechanisms, mineral interactions that affect acid–base and antioxidant status, and diet considerations to improve mineral status

“…Maintenance of normal plasma Mg concentration is almost totally dependent on daily dietary Mg absorption as there is no readily mobilizable Mg store. Cows with marginal or low extracellular Mg concentration are also likely to have low intracellular Mg concentration (Schweigel et al, 2009b). This is critically important because Mg is a major intracellular cation that is a necessary cofactor for enzymatic reactions that are vital to every major metabolic pathway.…”

“…This is the main mechanism used to transport Mg across the apical membrane when diet Mg and rumen Mg concentrations are low. Schweigel et al (2009b) have evidence that the amount of TRPM7 channel protein is upregulated when lumen Mg 2+ concentrations are low, which may help the animal adapt to a lower Mg diet.…”

<b>Inclusion of propylene glycol in the diet of sheep and its effect on their lambs’ protein and mineral metabolites

“…Likewise, concentration of minerals in fluids, such as in ruminants' blood and urine, is important to diagnose deficiencies of macro and microelements because, based on these analyses, it is possible to know the metabolic balance of a certain mineral (Schweigel, Voigt, & Mohr, 2009).…”

Magnesium homeostasis in cattle: absorption and excretion

“…At values below 0·9 mmol/l, both an adequate supply of Mg 2+ or impending clinical hypomagnesaemia are possibilities, so that a safe assessment of Mg 2+ status should involve a determination of urinary Mg 2+ excretion. Even then, difficulties in judging Mg 2+ status can be clearly seen in a study involving non-pregnant lactating cows with normal Mg 2+ intake (29–32·5 g/d) and plasma Mg 2+ concentration of 0·75–1·1 mmol/l ( 186 ) . After intravenous infusion of Mg 2+ and despite a slight increase in plasma Mg 2+ in four of the nine animals, the fractional renal Mg 2+ excretion decreased, indicating Mg 2+ retention after the Mg 2+ load and pointing towards a possible Mg 2+ deficit.…”