First-litter sows fitted with stomach cannulas were used to test the hypothesis that making gilts anabolic during lactation by providing them with extra nutrition would increase milk production and pig growth. Gilts were allocated to one of three dietary treatments after farrowing: 1) restricted, sows were fed 50% of their estimated ad libitum intake; 2) ad libitum, sows were encouraged to eat as much feed as possible; and 3) superalimented, sows were infused seven times daily through their cannula to achieve a 25 to 30% increase in energy intake in excess of that achieved by sows fed on an ad libitum basis. Milk production was estimated in mid- (d 10 to 15) and late (d 21 to 25) lactation by a modification of the isotope dilution technique. Milk production was similar between treatments in mid- and late lactation (P > .05), and this was reflected in a similarity in weaning litter weight (P = .238). Milk composition was similar also (P > .05) between dietary treatments. Superalimentation provided gilts with 38% more energy (P < .001) than gilts fed on an ad libitum basis, and they accrued live weight (5.1 kg) and backfat (1.8 mm) during lactation (P < .001). These data provide evidence that, unlike multiparous sows that show an increase in milk yield when made anabolic during lactation, primiparous sows seem to partition extra energy into body growth rather than into milk production.