Comparison of Four Magnesium Oxide Source s Each Fed at Three Dietary Concentrations to Lactating Cows'

2. Maximal lactational response in different experiments depended upon wha t Mg source was supplemented and the milk production level (stage of lactation) of cows . For midlactation cows supplemented with feed grad e magnesium phosphate, .48% total dietary Mg resulted in greatest milk yield . When midlactation cows were provided additional dietary Mg as Mg O maximal lactational response was obtained between .27 and .32% tota l dietary Mg. In one study with early lactation high producing cows, maxima l fat-corrected milk yield was achieved with .45% total dietary Mg . Milk fat percentage was increased in one of these experiments although the basa l diet would not be characterized as a milk fat-depressing diet .