Sixteen Holstein cows were used in a 4
x 4 Latin square design (four replicates)
to investigate the effect of feeding
calcium carbonate on feed intake, ruminal
fermentation, apparent total tract nutrient
digestibility, milk yield, and milk composition.
Supplementation of calcium carbonate
to diets that contained 60%
concentrate and 40% corn silage (DM
basis) decreased DM intake and milk
production and was not effective in
altering ruminal fluid pH, ruminal fluid
dilution rate or outflow, molar proportions
of ruminal fluid VFA, or synthesis
of milk fat and milk protein by dairy
cows. Calcium carbonate supplementation
to the diet tended to improve
efficiency of feed utilization (4% FCM/
DM intake). The exact site of action of
calcium carbonate, if any, is not known.
However, these data suggest that calcium
carbonate exerts little or no buffering
effect in the rmnen when the pH is 6 or
above regardless of its reactivity rate in
strong acid or its mean particle size. This
lack of effect is probably because of its
low solubility in ruminal fluid at pH
above 5.5.