CHANGES IN MILK-COMPOSITION DURING LACTATION IN 3 SPECIES OF INSECTIVOROUS BATS

Changes in milk composition are described for three species of free-ra nging insectivorous bats (Myotis lucifugus, M. velifer, and Tadarida b rasiliensis) from early to mid (peak) lactation. Dry matter and energy concentrations in milk increased from early to mid-lactation. In M. l ucifugus and T. brasiliensis, but not M. velifer, these increases were due largely to a rise in fat concentration, since protein and carbohy drate remained relatively constant. Energy content of milk (kJ.g(-1)) for each species from early through mid-lactation was related to dry m atter (DM) as follows: M. lucifugus (y=0.31 DM-0.32, r(2)=0.68), M. ve lifer (y=0.48 DM-5.08, r(2)=0.99), and T. brasiliensis (y=0.37 DM-1.51 , r(2)=0.61). Comparison of the effect of sampling method on milk comp osition of T. brasiliensis indicated that fat, dry matter, and energy concentrations increased significantly from pre-dawn to pre-noon sampl es. Relatively high fat and low water levels in T. brasiliensis milk m ay reflect the limited access that lactating females have to free wate r, as well as need to minimize mass of stored milk during long foragin g trips. Conversely, lower fat concentrations and higher water levels in milk in M. lucifugus and M. velifer may relate to the propensity fo r colonies of these two species to roost and forage near bodies of wat er. In addition, differences in milk fat concentrations observed among the three species may correlate to daily suckling schedules. Females of T. brasiliensis, for example, roost apart from and suckle their you ng on a regular daily schedule, whereas both species of Myotis roost w ith their pups and appear to suckle them on demand.