Pairs of littermate gilts from 51 litters were selected: one piglet with the highest birth weight (HW; 1.5 ± 0.2 kg) and the other with the lowest birth weight (LW; 1.0 ± 0.2 kg). Gilt pairs were killed at either fixed ages (80.8 ± 1.2 days; AG; 16 pairs), fixed body weight (35.2 ± 1.4 kg; WG; 16 pairs) or after first oestrus (EG; 19 pairs)