The assessment of dietary iron bioavailability using the piglet as an animal model for the human infant : a thesis presented in partial fulfilment of the requirements for the degree of Master of Master of Science in Nutritional Science at Massey University
The bioavailability of five different iron sources added to a bovine milk based formula was investigated in the anaemic, suckled piglet. These iron sources were ferrous pyrophosphate (FP), ferrous sulphate (FS), milk protein-iron complex (MPIC), ferrous lactate (FL), and haemin (Hm). Forty eight male piglets were removed from the sow at five days of age and randomly assigned to one of six treatment groups (n=8). Iron depletion was achieved in two ways: firstly, by withholding the iron injection usually given to these piglets at birth, and secondly, by feeding the piglets an iron-deficient formula throughout an eleven day adjustment/iron-depletion period. The five formulas containing the supplementary iron and one formula containing no iron (control diet) were bottle-fed to the piglets (336g of liquid formula/kg bodyweight/day) seven times daily for a 25 day repletion period. Analysis of the formulas revealed that iron levels in each of the five iron treated formulas varied over a range of 6.0-8.3 mg/l00g of powdered formula. Iron bioavailibility was assessed in the piglets by a haemoglobin repletion assay. Blood was collected from the anterior vena cava of the piglets on days 0, 11, 24, and 36 of the trial, and the piglets were weighed every three to four days throughout the 25 day repletion period. Blood haemoglobin concentration, haematocrit, unsaturated iron binding capacity, and piglet liveweights were used as indicators of iron status in the piglets. Haemoglobin Repletion Efficiency (HRE%), a measure of the proportion of ingested iron that is incorporated into haemoglobin in the body, was calculated to correct for differences in the iron content of the formula and differences in iron intake by the piglets. The HRE% for the FP, FS, MPIC, FL, and Hm fortified formulas were 23.5, 35.8, 38.0, 32.9, and 3.2%, respectively. There were no significant differences, however, in the mean blood haemoglobin concentrations, haematocrits, HRE% and UIBC for piglets fed the FS, MPIC, or the FL fortified formulas half way through, and at the end, of the repletion. This implied that there were no differences in the bioavailability of these iron sources. In contrast, these parameters were all significantly lower (P>0.05), for the piglets fed either the FP or the Hm formulas. Based on relative biological value, the bioavailability of each iron source, when ranked in order from highest to lowest, was MPIC<FS<FL<FP<Hm. These findings have important implications for the development of iron-enriched milk products destined for human consumption.