Birth regulates the development of suckling behavior. (A) The experimental procedure to induce preterm birth using mifepristone. Mifepristone (Mife) or saline was injected between 21:30 and 22:30 at 16 dpc. (B) Nipple attachment latency was reduced markedly earlier in preterm pups than in full-term pups. At 25.75 dpc, nipple attachment latency was significantly smaller in preterm pup than in full-term pups (*p < 0.05, Mann–Whitney U test, mean ± SD). (C) Body weight was not affected by preterm birth (p > 0.4, Student’s t-test, mean ± SD). (D) The righting reflex latency was not affected by preterm birth (p > 0.4, Student’s t-test, mean ± SD).