Published online by Cambridge University Press: 09 March 2007
1. Intestinal radiocalcium absorption was measured in goats by a double-isotope technique involving injection of 45CaCl2 intravenously and 47CaCl2 into the abomasum. Cumulative absorption of radiocalcium was calculated by deconvolution analysis form curves of plasma radioactivity.
2. Repeated measurements at 2 d intervals gave highly reproducible results (r 0.94, P < 0.001). No systematic difference between two consecutive measurements was observed. A good agreement between absorption of radiocalcium from simultaneously administered 47CaCl2 and 45Ca-labelled hay (r 0.93, P < 0.001) seems to justify the use of inorganic 47Ca as a tracer for Ca in ruminant diets.
3. Two- to three-fold increases in radiocalcium absorption 48 h after oral treatment with 1,25- dihydroxycholecalciferol or leaves of Solanum malacoxylon showed the usefulness of the method in situations of rapidly changing Ca absorption.
4. Endogenous adaptations in intestinal radiocalcium absorption from 20 to 43% were observed in lactating goats when Ca intakes decreased from 12 to 4 g/d.
5. It is concluded that the double-isotope technique is a suitable method for studies of Ca absorption in ruminants when tracer is introduced into the abomasum. The test is completed in 3–4 h and may therefore be used in situations where the absorption of Ca undergoes rapid changes.