Twenty-four primiparous sows were allocated at farrowing to a high (H: 5.5-6 kg feed/day) or a low (L: 2.5-3 kg/day) level of feeding. Litters (8-10 piglets) were weaned at 28+/-2 days. Serial blood samples were collected 1 day before weaning (W-1), in the hours following weaning (W) and 1 day after (W + 1). L sows lost significantly more weight (38 versus 15 kg) and backfat (5.3 versus 2.3 mm) during lactation than H sows. On day W-1, L sows had higher mean concentrations of NEFA (P < 0.01) and GH (P < 0.1 ) and lower concentrations of insulin and IGF-I (P < 0.05) than H sows. Mean concentrations of glucose and cortisol did not differ between groups of sows. On day W + 1, these parameters were not different between treatments, except IGF-I concentrations which remained lower in L than in H sows (P < 0.05). We conclude that lactating primiparous sows alter secretion of metabolic hormones to favour mobilization of body reserves to support milk production. Low insulin and IGF-I may be involved in reduced ovarian activity at and after weaning, through LH-dependent and independent pathways.