Immunocastration is a method for raising male pigs without surgical castration and with reduced boar taint. It consists in two vaccinations against GnRH. After the second vaccination (V2) performed a few weeks before slaughter, pigs increase their feed intake whereas protein deposition remains constant. The dietary protein content should then be reduced to limit N excretion but the kinetics of protein reduction may differ between animals. The objective of the trial was to determine individually the optimal dietary amino acid to energy ratio. For that purpose, 75 male pigs were housed in a stable equipped with one weighing scale and eight automatic feeders filled with two diets varying in their amino-acid content (0.96 and 0.40 g DIS lys/MJ NE). The automatic feeders allowed mixing the two diets in proportions depending on the body weight of the pig and the expected daily gain and feed intake. From 30 kg body weight to V2, individual proportions of the mixture were determined. The V2 was performed at 127 days of age (74.3 kg body weight) and animals were slaughtered at 164 days of age. From V2 onwards, the pigs were allocated to 3 groups, that either 1/received until slaughter a mixture of the two diets whose proportions equalled the individual proportions measured the week before V2; 2/received a mixture of the two diets, whose proportions were daily and individually calculated as before V2 or 3/were proposed the high and the low protein diets so that each pig can adapt itself the composition of its intake. Feed intake from V2 to slaughter did not significantly differ between groups (3.42 kg/d). The BW at slaughter (115.8 kg) and carcass weight (91.3 kg) did not also differ between groups. The lysine intake was the highest for group 1 (28.4 g/d) and the lowest for group 2 (21.5 g/d). Finally, the efficiency of lysine deposition was higher for groups 2 and 3 than for group 1 (59, 55 and 47% of lysine intake, respectively), which suggests that dietary protein level can be decreased up to 25% after V2 in immunocastrated pigs. This study is part of the ERA-NET project SuSI (ANR-16-SUSN-0004).