H. Abudamir et al., EFFECTS OF DIETARY ACIDITY ON CALCIUM BALANCE AND MOBILIZATION, BONE MORPHOLOGY AND 1,25-DIHYDROXYVITAMIN-D IN PREPARTAL DAIRY-COWS, Research in Veterinary Science, 56(3), 1994, pp. 310-318
The effect of an acid or alkali diet was investigated in 14 mature dai
ry cows during the last 28 days of pregnancy. The acid diet reduced th
e incidence of parturient hypocalcaemia compared with the alkali diet
and was associated with higher blood ionised calcium and plasma chlori
de concentrations and lower blood pH and acid-base excess before partu
rition. Plasma 1,25-dihydroxyvitamin D concentrations before parturiti
on were increased by the acid diet but the concentrations of parathyro
id hormone and intact 1-86 parathyroid-hormone-related peptide were un
affected. The estimated fractional calcium absorption and calcium mobi
lisation rate during an ethylenediamine tetraacetic acid infusion were
increased by the acid diet 14 days before parturition. Cortical bone
remodelling occurred in all the animals during late pregnancy but was
particularly evident in the cows given the acid diet. The data suggest
that an acid diet ameliorates parturient hypocalcaemia by enhancing c
alcium mobilisation before parturition by increasing calcium absorptio
n and bone resorption, these increases possibly being mediated by incr
eases in the plasma concentration of 1,25-dihydroxyvitamin D.