Many female bats give birth to a single large young that is weaned at about 90–95% adult size and about 70–80% adult postpartum mass. The need for young to become independent fliers as quickly as possible presumably drives this burdensome development. We considered whether minerals or nitrogen in milk could limit reproductive and developmental capacity in bats. Milk samples were collected during the course of lactation from captive Artibeus jamaicensis and Phyllostomus discolor with known-aged young. Milk mineral (calcium, magnesium, sodium, potassium, and iron) and nitrogen concentrations did not significantly change during the course of lactation, except for sodium, which decreased in A. jamaicensis. When compared with other bats, concentrations of minerals and nitrogen in milk were weakly associated with phylogeny. We calculated daily accretion rates and total amounts of minerals and nitrogen in the body of young bats for each day of development. We also present calculations of the mass of milk required each day to meet accretion of minerals and nitrogen throughout the course of postnatal growth. From these analyses, we found that, except for calcium, minerals and nitrogen in milk were present in concentrations that exceeded the needs of developing young.