Parathyroid hormone-related peptide (PTHrP) plays a major role in the regulation of bone growth in the fetus and the neonate. In pregnant and/or lactating ruminant animals, the PTHrP secreted by fetal parathyroid glands and placental membranes stimulates calcium placental transfer from the dam to the fetus. PTHrP also modulates myometrial uterine activity. The expression of the PTHrP gene in pregnant uterus is under the control of mechanical stretch induced by uterine distension following fetal growth. Thus PTHrP controls the rhytmicity and/or force of myometrial contractions during pregnancy Since uterine contractions severely depress blood flow, another possibility is that PTHrP might act to dilate uterine (and placental) blood vessels and assure adequate blood flow to the uterus and feto-placental unit. Conversely, in ewes and goats, the PTHrP released by the lactating mammary gland regulates mammary blood flow and calcium and phosphorus mammary secretion. In neonates, milk PTHrP might control gut motility and calcium and phosphorus intestinal absorption. Thus, by controling calcium placental transfer, myometrial uterine activity, placental and mammary blood flow, milk calcium and phosphorus concentration, and, possibly, calcium and phosphorus intestinal absorption in the newborn, PTHrP regulates skeletal growth during fetal and postnatal periods.