The impacts of a teat being suckled or not in first parity on its development, gene expression, and milk yield in the next parity were studied. Forty-seven first-parity sows (Sus scrofa) were divided into 2 groups: i) the same teats suckled in 2 subsequent lactations (controls, CTL; n = 22); and ii) different teats suckled in 2 subsequent lactations (treated, TRT; n = 25). In the first lactation, over half of the teats (Teats 1, 2, 5, 6, and 7 from 1 side of the udder, and Teats 3, 4, and 7 from the other side) were sealed with tape so that they were nonfunctional. During the next lactation, the CTL group had the same teats sealed as in the first lactation, whereas the opposite teats were sealed for the TRT group. In both parities, litters were standardized to 7 piglets around birth and to 6 piglets (1 piglet per available teat) at 48 h postpartum. During the second lactation, piglets were weighed at birth and on d 2, 4, 7, 14, 21, 35, and 56 postpartum. Weaning was at 17 ± 1 d of age. Behavioral measures were obtained (using 24-h video recording) on d 3 and d 10 of lactation on 15 sows per treatment to evaluate satiety of piglets, using aggressiveness and nursing behavior as indicators. At weaning in the second lactation, 16 sows per treatment were slaughtered and 4 functional mammary glands were collected for compositional analyses and parenchyma from 2 nonfunctional glands was collected to measure mRNA abundance for selected genes. Piglets from CTL sows weighed 1.12 kg more than piglets from TRT sows (P < 0.05) on d 56, and functional mammary glands from CTL sows contained more parenchymal tissue, more DNA, and more RNA (P < 0.01) than those from TRT sows. The relative mRNA abundance of prolactin in parenchymal tissue tended to be greater in CTL than TRT sows (P < 0.10). Behavioral measures indicated a greater hunger level for piglets using teats that were not previously suckled. Current findings clearly show that teats that were suckled in first lactation produce more milk and have a greater development in the second lactation than nonsuckled teats.