A window of opportunity for maternal programming of neonatal development is open in the first few days of life as a consequence of nursing. Colostrum (first milk) supports neonatal development by providing a conduit for delivery of milk-borne bioactive factors, exemplified by relaxin, from mother to offspring as proposed in the lactocrine hypothesis. Relaxin, a prototypical milk-borne bioactive factor, is detectable in colostrum from multiple species, including the pig. Thus, relaxin serves as a model for understanding lactocrine signals that support development of neonatal tissues
