title: Intestinal radiocalcium absorption in the goat: measurement by a double-isotope technique.
abstract: 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. Repeated measurements at 2 d intervals gave highly reproducible results (r 0.94, P less than 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 less than 0.001) seems to justify the use of inorganic 47Ca as a tracer for Ca in ruminant diets. 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. 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. 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.
mesh_terms: D000818:Animals; D002117:Calcitriol / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002136:Calcium, Dietary / Q000008:administration & dosage; D005260:Female; D006041:Goats / Q000378:metabolism*; D007408:Intestinal Absorption / Q000187:drug effects; D007774:Lactation; D008722:Methods; D010945:Plants, Edible; D011247:Pregnancy; D013997:Time Factors
chemical_list: D002132:Calcium Radioisotopes; D002136:Calcium, Dietary; D002117:Calcitriol; D002118:Calcium