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Variability in bodyweight (BW) among pigs complicates the management of feeding strategies and slaughter. Including variability among individuals in modelling approaches can help to design feeding strategies to control performance level, but also its variability. The InraPorc model was used to perform simulations on 10 batches of 84 crossbred pigs each to characterise the effect of feeding strategies differing in amino acid supply or feed allowance on the mean and variation in growth rate. Results suggested that a feed restriction reduces the coefficient of variation of BW at first departure for slaughter (BW1) by 34%. Growth performance obtained from an in silico simulation using ad libitum and restricted feeding plans was compared with results obtained in an in vivo experiment on a batch of 168 pigs. Pigs were offered feed ad libitum or were restricted (increase in feed allowance by 27 g/day up to a maximum of 2.4 and 2.7 kg/day for gilts and barrows, respectively). A two-phase feeding strategy was applied, with 0.9 and 0.7 g of digestible lysine per MJ of net energy (NE) in diets provided before or after 65 kg BW, respectively. Actual growth was similar to that obtained by simulation. Coefficient of variation of BW1 was similar in vivo and in silico for the ad libitum feeding strategy but was underestimated by 1 percentage point in silico for the restriction strategy. This study confirms the relevance of using simulations performed to predict the level and variability in performance of group housed pigs.

The effect of dietary NE content on feed intake and performance of pigs was investigatedusing crossbred barrows with initial and fi nal BW of approximately 35 and 110 kg, respectively. Pigs werehoused individually and allowed ad libitum access to feed. Pigs were randomly allotted to 6 wheat andsoybean meal-based diets (8.1, 8.7, 9.3, 9.9, 10.5, and 11.1 MJ NE/kg) with 16 pigs/diet. Ratios betweenstandardized ileal digestible AA and NE were similar in all diets. Over the entire experiment, increasein dietary NE concentration was associated with a decreased ADFI (3.216, 3.216, 3.122, 2.910, 2.732,and 2.684 kg/d, respectively, for diets containing 8.1 to 11.1 MJ NE/kg; linear, P < 0.01). The NE intakeincreased as dietary NE increased from 8.1 to 11.1 MJ NE/kg (26.04, 27.98, 29.03, 28.81, 28.68, and 29.77MJ/d, respectively; linear, P < 0.01, and quadratic, P= 0.06). Average daily gain increased when dietaryNE concentration increased (1.046, 1.126, 1.135, 1.177, 1.156, and 1.152 kg/d, respectively, for dietscontaining 8.1 to 11.1 MJ NE/kg; linear and quadratic, P < 0.01). The increase in dietary NE concentrationwas associated with an increase in dressing percentage (76.5, 77.0, 77.4, 78.0, 78.2, and 78.4% of BW;linear, P < 0.01) but no differences in lean percentage (58.3, 57.9, 58.0, 57.3, 58.1, and 56.4% of HCW,respectively, for diets containing 8.1 to 11.1 MJ NE/kg; P = 0.12). When dietary NE concentrationincreased from 8.1 to 11.1 MJ/kg, the G:F increased (0.326, 0.352, 0.364, 0.405, 0.425, and 0.428 kg/kg,respectively; linear, P < 0.01), but the G:F expressed using the NE system did not change (G:F, 39.97 g/MJNE; P = 0.44). When adjusted to the same dressing yield and lean percentage, the differences in adjustedADG increased among treatments, but the adjusted G:F expressed using the NE system was not infl uencedby dietary energy concentration. These results confirm the ability of individually housed pigs to adjust theirspontaneous feed intake over a very wide range of NE concentrations (8.7 to 10.5 MJ/kg). Under commercialconditions, pigs may experience less variation in ADFI than the results obtained in this experiment because ofdifferences in dietary energy concentrations. However, it seems that only a severe reduction in dietary energyconcentration will be effective in restricting energy intake of pigs that are allowed ad libitum access to feed