Effect of granulated magnesium oxide on the production and composition of milk by cows fed cereal grain and either conserved fodders or pasture

Abstract

Milk production and composition were measured in 54 Holstein-Friesian dairy cattle fed 8.4 kg DM crushed barley grain daily and either supplemented or not with granulated magnesium oxide (MgO). The supplement was offered for 2 sequential test periods of28 days. During the first test period, cows were offered conserved pasture, conserved cereal crops, and grazed pasture. During the second test period they were only grazed on pasture. In the first period MgO had no effect (b0.05) on milk production or composition. During the second period, more (P<0.05) milkfat was produced by cows offered the MgO supplement than by unsupplemented cows (0.73 v. 0.69 kg/day). During this period the breakeven net milkfat price was calculated as $A1.23/kg.