MODELING THE DEVELOPMENT OF UTERINE COMPONENTS AND SOW BODY-COMPOSITION IN RESPONSE TO NUTRIENT INTAKE DURING PREGNANCY

The components of the gravid uterus in the sow - fetuses, fluids and membranes - were modelled on the basis of published dissection data, in order to predict maternal tissue composition changes through gestation. Daily rates of protein and lipid accretion in the gravid uterus, derived by differentiation, were met with first priority on available protein and energy intake. Available nutrients were then partitioned between maternal protein accretion and protein support costs, energy support costs and maternal lipid accretion, in that order. The efficiency of energy accretion as protein and lipid in uterine tissue ranged from 0.47 to 0.73, when calculated from estimates of k(p) and k(f) applied to protein and lipid accretion in utero. The rates of protein and lipid accretion in maternal tissue were reduced to differing extents with the advancement of pregnancy. Hence, estimates of the ratio of maternal protein to lipid in weight gain varied with stage of gestation, litter size and protein and energy intake. There was no evidence of maternal tissue hydration or protein anabolism; these effects were localised in uterine tissues. Model predictions closely approximated the sow's response to nutrient intake and nutrient partitioning during pregnancy, allowing body composition changes to be predicted in anticipation of lactation.