Calcium digestibility in cows as influenced by the excess of alkaline ions over stable acid ions in their diets.

1. Statistical analyses were carried out on results obtained under strictly-controlled conditions in metabolism stalls with forty-one different rations fed to 127 adult non-pregnant dry cows, and with fourteen other different rations fed to thirty-five adult non-pregnant lactating cows that had calved 2-6 months earlier and whose daily milk production ranged from 11 to 20 kg. 2. Correlations between calcium digestibility and values for the sum of the alkaline ions sodium and potassium minus the sum of the stable acid ions chloride, sulphate and phosphate were calculated for all fifty-five experimental diets. 3. The results showed that the excess of the anions over the cations, in rations maintaining a positive Ca balance but not in rations allowing a negative Ca balance, increases the absorption of Ca from the intestine. Phosphorus, not alone but with chloride and sulphate, is the most important component of this effect.