Lactocrine signaling is defined as transmission of bioactive factors from mother to offspring as a consequence of nursing. Lactocrine transmission of signaling molecules may be an evolutionarily conserved process through which bioactive factors necessary for support of neonatal development are delivered postnatally. Dependence on maternal resources for development in eutherian mammals extends into neonatal life for at least that period of time when nutrition is obtained solely from first milk (i.e., colostrum). Data for the pig (Sus scrofa domesticus) provide evidence of lactocrine mediated effects on development of the female reproductive tract and other somatic tissues. Porcine uterine gland development, an estrogen receptor-alpha (ESR1)-dependent process, begins within 2 d of birth [postnatal day (PND) 0]. A lactocrine-driven, ESR1-mediated process was proposed as a regulatory mechanism governing onset of uterine gland development and endometrial maturation in the neonatal pig. Gilts maintained in a lactocrine-null state for 2 d from birth by milk-replacer feeding displayed altered patterns of endometrial gene expression and retarded uterine gland development by PND 14. In lactocrine-null gilts, inhibition of endometrial and cervical ESR1 and vascular endothelial growth factor (VEGFA) expression observed on PND 2 persisted to PND 14, even after gilts were returned to nursing on PND 2. Collectively, data support a role for lactocrine signaling in regulation of critical neonatal developmental events. Maternal lactocrine programming of postnatal development may help to insure healthy developmental outcomes. A systems biology approach will be required to define and understand mechanistic dynamics of lactocrine signaling events that may ultimately connect genotype to phenotype and establish the parameters of reproductive potential.