Accretion of Nitrogen and Minerals in Suckling Bats, Myotis velifer and Tadarida brasiliensis

Levels of nitrogen, sodium, potassium, magnesium, calcium, and iron were determined for suckling young of known-age, lactating Myotis velifer and Tadarida brasiliensis, and milk from T. brasiliensis nursing known-age young. From birth to weaning, relationships of both nutrient concentrations and nutrient accretion to age are similar for both species but differ for each nutrient and generally reach adult concentration by weaning. While total mass of body sodium and potassium reach adult levels in both species well before weaning, levels of other elements do not. Although comparable data are limited, element concentrations in suckling bats are similar to those for other suckling small mammals and nestling birds. Growth requirements for measured nutrients in these bats are lower than published values for rodents. Most mineral nutrients that were measured in milk for T. brasiliensis varied with stage of lactation and were comparable in concentration with milk of other mammals. Using daily accretion of nutrients and their concentrations in milk, we calculated the minimal mass of milk needed to meet growth requirements in suckling T brasiliensis. Among measured nutrients, calcium is the limiting nutritional factor that determines mass of milk needed by suckling young during postnatal growth.