Diet calcium and pH versus mineral balance in Holstein cows 84 days pre- to 2 days postpartum

Sixteen dry Holstein cows were assigned four groups combining either .2 or 2.1% calcium and pH of either 4.5 or 6.1 in a 2 X 2 factorial arrangement of treatments to study the effect of diet calcium 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 calcium and acidity (lower pH) diets. Calcium nutriture was improved by more acid diets. More total calcium was apparently absorbed (26 and 7 g) when the diet contained 2.1% calcium, but the .2% calcium 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 calcium occurred with the higher calcium treatment at 2 days postpartum. Magnesium and phosphorus utilizations were improved with lower diet calcium. Although experimental treatments had no significant effect on blood minerals, serum calcium decreased 12% 2 days postpartum. A better calcium nutriture was provided by the higher calcium diets when the diets maintained a positive balance for magnesium and phosphorus.