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In feeding and digestion trials with lactating dairy cows fed complete mixed diets ad libitum without or with limestone buffer, the complete dry matter ratio was 50:50 corn silage to concentrate. During the 44-wk feeding trial, lactating cows fed a complete diet containing 2.71% limestone had similar intakes of dry feed but produced 7.3% more milk than cows fed a complete diet containing .14% limestone. In digestion trials at maintenance intakes of feed, digestibilities of dry matter, energy, starch, cell wall, and crude protein were higher than when intakes of feed ranged from 2.8 to 3.4 multiples of maintenance during lactation. Addition of 2.71% limestone to the diet at the higher intakes of feed during lactation increased digestibility coefficients for dry matter from 66.1 to 69.5%, energy from 65.4 to 68.3%, starch from 85.9 to 94.6%, cell wall from 51.3 to 55.1%, and crude protein from 65.7 to 67.8%. Limestone as a buffer for this diet of high energy improved both production and diet efficiency possibly by maintaining an environment in gastrointestinal tract more desirable for utilization of both starch and cell wall at intakes of feed above maintenance.

A series of tests were made on cement kiln dusts to determine their capacity to sequester protons and to identify the active agents. The pH stat titration technique indicated little difference among kiln dusts in their capacity to neutralize acids. All kiln dusts were less reactive than calcium oxide but similar to reagent and feed grade calcium carbonates. Examination of kiln dusts by X-ray diffraction indicated that the major form of calcium was calcium carbonate and that little, if any, calcium was present as the oxide or hydroxide. The calcium carbonate in cement kiln dust, determined by the carbonate test, varied from 49.5 to 85.7%. All kiln dusts were much more reactive at pH 3.0 than at 6.0. Cement kiln dusts that did not show a favorable response when fed to animals showed less reactivity at pH 6.0 than dusts eliciting a favorable animal response. The active agent appears to be calcium carbonate in a finely divided state.