Diet Calcium and pH Versus Mineral Balance in Holstein Cows 84 Days Pre- to 2 Days Postpartum

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Abstract
Sixteen dry Holstein cows were assigned 4 diet groups combining either .2 or 2.1% Ca and pH of either 4.5 or 6.1 in a 2 .times. 2 factorial arrangement of treatments to study the effect of diet Ca and acidity (pH) on voluntary intake of dry matter, mineral metabolism, and blood constituents. The 86-day experiment was started 84 days prepartum and completed 2 days postpartum. Voluntary dry matter ingestion tended to be higher with higher Ca and acidity (lower pH) diets. Ca nutriture was improved by more acid diets. More total Ca was apparently absorbed (26 and 7 g) when the diet contained 2.1% Ca, but the .2% Ca diet resulted in a higher apparent percent absorption (25 and 17%) during the dry period. An increased apparent absorption (70 and 5 g) and utilization of diet Ca occurred with the higher Ca treatment at 2 days postpartum. Mg and P utilizations were improved with lower diet Ca. Although experimental treatments had no significant effect on blood minerals, serum Ca decreased 12% 2 days postpartum. A better Ca nutriture was provided by the higher Ca diets when the diets maintained a positive balance for Mg and P.