How to assess bioavailability of zinc sources?
Dr Daniel Brugger (University of Zurich, Switzerland) and Dr Sergio Vieira (Universidade Federal do Rio Grande do Sul, Brasil) reviewed the challenges to estimate trace mineral requirements of animals. Measuring the mineral quantity in the feces under-estimates endogenous losses due to active excretion and cell debris. When comparing the relative bioavailability of trace minerals from different sources, dose response studies with finely-graded differences in dietary metallic concentrations must be applied from deficiency state to mild oversupply.
Threshold (breakpoint) is the gross zinc requirement at given experimental conditions :
Broken-line response of two zinc sources :
Even absorbed, not all retained amounts of trace elements are transferred into a biologically active form. Without more appropriate biomarkers of mineral status, researchers have to work with invasive methods to assess animal requirements and bioavailability of sources (see https://animine.eu/research-science-11/).
Based on zinc concentration in the bone, Zn requirement of growing broilers seems to plateau at less than 90 mg/kg in the complete feed :