As mentioned before, parameters of the basic growth model (i.e. BW, FI and PDmax) were adjusted and consecutively fixed to match experimental values as closely as possible. As indicated in Table 4, assuming a PDmax of 150 or 160 g/day for experiments 1 and 2, respectively, led to reasonable predictions of average daily gain and feed consumption. In experiment 1, predictions of protein and lipid mass were similar to observations whereas the FA mass was slightly lower than observed. In contrast, the model overestimated backfat lipid and linoleic and linolenic acid mass. The predicted FA composition was similar to that observed, except for palmitic acid and minorFA, which were slightly over- and underestimated by the model, respectively. In experiment 2, predictions of body composition were quite different from the observed results. Protein mass was slightly underestimated whereas the model largely overestimated lipid and FA mass. Also backfat lipid, and linoleic and linolenic acid mass were overestimated by the model. Backfat stearic and oleic acid composition were systematically overestimated whereas palmitic and linoleic acid were underestimated. Predicted values for the other FA were reasonable but these only represent 50 g/kg of the total FA. As for the body lipid, the model largely overestimated the perinephric lipids (>45%) and the corresponding linoleic and linolenic acid mass (Table 5). The FA composition was rather different from the results for all diets although the composition for the poly-unsaturated FA was reasonably well predicted. Differences concern mainly de novo synthesized FA; palmitic and stearic acid contents were largely underestimated (20%) whereas oleic acid content was overestimated (>35%).