Statistical research on the fate of dietary mineral elements in dry and lactating cows: I. Calcium

Summary

Statistical analyses were carried out on the data obtained under strictly controlled conditions in metabolism stalls with 41 different rations fed to 127 adult non-pregnant dry cows, and with 14 other different rations fed to 35 adult non-pregnant lactating cows that had calved 2–6 months earlier and whose daily milk production ranged from 11 to 20 kg. The authors have calculated and studied the correlations between faecal and urinary calcium losses, calcium excretion in the milk, digestible calcium, and calcium balance, and the 75 other nutritive factors which were analysed for each of the 55 above-mentioned experimental diets. The results showed that calcium metabolism is regulated in the digestive tract, and the fact that the lactation calcium requirements increase at the same time as the amounts of digestible calcium and the calcium balance corroborates this statement. But except for this endogenous factor of resorption, the fate of the dietary calcium does not depend on the ingested amounts but on the nature itself of the components of the diets and their proportions in the diets. Cereals, and especially barley, have from this point of view a particular beneficial effect. These factors act on the absorption of calcium and thus directly on the balance, since the daily urinary excretion of calcium is generally small and independent. It has also been demonstrated that the balance is not inevitably negative in cows with a daily milk production of 11–20kg, and that a careful composition of the rations should enable one to equilibrate it.

The other nutritive factors do not work on calcium utilization, but a close parallel exists between digestibility, urinary excretion and balance of both calcium and magnesium.