Abstract

SEPULVEDA, Pilar; WITTWER, Fernando  and  NORO, Mirela. Blood and rumen indicators of magnesium balance in dairy cows on grazing and supplemented with magnesium oxide or magnesium chelate. Zootecnia Trop. [online]. 2013, vol.31, n.1, pp.5-15. ISSN 0798-7269.

The aim of this study was to evaluate magnesium supplementation from an organic source (MgO) versus an inorganic form (MgQ) on magnesium (Mg) balance in lactating dairy cows grazing on a permanent pasture at the end of spring. Thirty lactating Holstein cows and four ruminal-fi stulated cows were used. Study was divided in two experiments: Experiment 1, fi stulated cows were given Mg supplementation as an oral drench after morning and afternoon milkings, without supplementation (Control) 30g/cow of Mg as MgO and 30g/cow of Mg as MgQ. Ruminal fl uid and blood samples were obtained at 8:30, 10:30, 13:00, 17:30, 19:30, 22:00 y 02:30 h to determine rumen pH, Mg, potassium (K) and ammonia (NH4+) concentrations and Mg concentration on plasma. Urine samples were also obtained at 8:30, 13:00, 17:30 y 22:00 h to determine clearance of urine Mg (CUM). Experiment 2, three groups of 10 lactating cows each (C, MgO y MgQ) were used during a total time of 20 days where: 0 -5 d (baseline period) 6 -15 d (supplementation period) and 16 -20 d (post-supplementation period). Ruminal fl uid y blood samples were obtained on days 0, 5, 10, 15 y 20 to determine same parameters as for experiment 1. In experiment 1, magnesemia was higher in supplemented cows and no differences among treatments were found in experiment 2. CUM values were similar among treatments in both experiments. In experiment 1, ruminal Mg concentrations increased in cows receiving MgQ compared to control cows and in experiment 2, were similar among treatments. In both trials, the ruminal pH of cows supplemented with MgQ were lower than those supplemented with MgO. It is concluded that MgO y MgQ have a similar effect on the Mg metabolic balance in dairy cows on pasture, Nevertheless MgQ tends to acidify the ruminal pH.

Keywords : magnesemia; magnesium chelate; magnesium oxide; grazing; dairy cow.

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