Limestone Buffers in Complete Mixed Rations for Dairy Cattle

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Abstract
In 2 feeding trials lactating dairy cows were fed limestone and in 1 trial growing dairy heifers were fed Mg-limestone-buffered rations. Complete mixed rations based on corn silage and corn grain were fed ad lib. In trial 1, cows fed a ration with 2.76% limestone consumed 7.36% less dry matter of feed than cows fed a ration containing .11% added limestone, with no effect on milk production. In trial 2, cows fed a ration with 2.71% limestone had similar feed intakes and milk production but gained more weight than cows fed a ration with .01% limestone. Heifers fed a ration supplemented with Mg limestone gained .49 kg more weight per day and made more efficient use of feed than heifers fed the nonsupplemented ration. Limestone increased fecal pH from 5.99 to 6.62 in trial 1, 6.13 to 6.57 in trial 2 and a decreased loss of starch in feces. Mg limestone increased fecal pH from 6.37 to 6.76 and decreased starch in feces from 5.60 to 1.14%. In these trials both limestone and Mg limestone increased fecal pH, reduced starch losses in the feces and improved feed efficiency.