Effects of magnesium oxide and magnesium alloy rumen boluses on plasma and urinary magnesium and calcium concentrations in reindeer (Rangifer tarandus tarandus)

The objective was to study MgO and Mg alloy rumen boluses as Mg supplements for reindeer (Rangifer tarandus tarandus) by following the plasma and urinary Mg and Ca concentrations. In the first 116-day experiment, varying amounts of lichens or commercial reindeer feed were given to nine adult female reindeer allocated into three groups. Group 1 received lichens ad libitum for 76 days, followed by commercial reindeer feed for 40 days. Group 2a received lichens ad libitum for 6 days, followed by lichens at 80% of the ad libitum intake for 51 days with 10 g of MgO per day per animal and by lichens ad libitum for 59 days with MgO supplement. Group 2b was fed as group 2a, but without MgO supplementation. In the second experiment, six 10-month-old female reindeer calves with rumen cannulae were fed lichens for 18 days and then supplemented with two Mg alloy rumen boluses for 26 days of which they were fed commercial reindeer feed and some lichens for the last 11 days. The mean plasma Mg concentration of the animals supplemented with MgO increased from 0.73 to above 1 mmol/l when lichens were given as the only feed, whereas in the unsupplemented animals with otherwise the same feeding it declined below 0.70 mmol/l, which was considered hypomagnesemic, after 18 days. The differences in plasma Mg concentrations between the supplemented and unsupplemented groups were significant at all times when the animals fed on lichens (P < 0.05). The mean plasma Mg concentration of group 1 increased from 0.60 to 1.00 mmol/l in 5 days when the commercial reindeer feed was started. The mean plasma Ca concentrations were lower, but only occasionally below 2.2 mmol/l, which was considered hypocalcemic, in the reindeer receiving supplemental MgO compared to unsupplemented animals. Supplementation withMgalloy rumen boluses increased plasmaMg (P < 0.01), with amean peak concentration (±S.E.) of 1.13±0.02 mmol/l occurring 2–6 days after the insertion of the boluses, followed by a gradual decline after that. The plasma Ca concentration decreased, with a mean minimum concentration of 2.36 ± 0.02 mmol/l (P < 0.01) occurring 1–5 days after the insertion of the boluses. The loss in bolus weight was 10.8–24.6 g per bolus, and the calculated release of Mg from the two boluses ranged between 0.34 and 2.24 g per day. The urinary Ca/creatinine and Mg/creatinine ratios (mmol/mmol)increased after the insertion of the Mg alloy rumen boluses, suggesting that an increased Mg intake may lower the plasma Ca concentration by increasing the excretion of Ca into urine. In conclusion, both Mg supplements increased the plasmaMg concentration of reindeer, but the same plasmaMg level was also achieved by commercial reindeer feed. The considerable variation in the bolus weight loss suggests that their use as a Mg supplement may be limited to conditions where no other form of Mg supplementation or commercial reindeer feed can be provided. © 2003 Elsevier B.V. All rights reserved