Intrinsic labeling of milk iron: effect of iron status on isotope transfer into goat milk

Abstract

Extrinsic labeling with radioiron is commonly used in studies on bioavailability of iron in milk. Because of differences in the distribution of added radioiron and native iron among ligands in milk, we found it important to explore the possibility of intrinsic labeling of milk iron. In this study, we have evaluated different conditions in the lactating goat to optimize transfer of 59Fe into milk. Maximum 59Fe concentration in milk was found at 10–15 hr post injection, indicating a carrier-mediated process. After iron depletion induced by bleeding, iron transfer into milk in the mammary gland was found to be low. After iron repletion, however, iron transfer increased. This study suggests that maternal iron status affects iron transfer into milk and that during iron depletion, hematopoietic organs may have higher affinity for transferrin-bound iron than the mammary gland. Iron transport into milk was lower in dairy goats than in a young goat which had not been used in milk production. This suggests that mammary development may enhance iron uptake in the gland, possibly via transferrin receptors.