MILK-COMPOSITION AND LACTATIONAL OUTPUT IN THE GREATER SPEAR-NOSED BAT, PHYLLOSTOMUS-HASTATUS

Growth rates of mammalian young are closely linked to the ability of t he mother to provide nutrients; thus, milk composition and yield provi de a direct measure of maternal investment during lactation in many ma mmals. We studied changes in milk composition and output throughout la ctation in a free-ranging population of the omnivorous bat, Phyllostom us hastatus. Fat and dry matter of milk increased from 9 to 21% and fr om 21 to 35% of wet mass, respectively, throughout lactation. Energy i ncreased from 6 to 9 kJ.g(-1) wet mass, primarily due to the increase in fat concentration. Total sugar levels decreased slightly but non-si gnificantly. Mean sugar level was 4.0% of wet mass. Protein concentrat ion increased from 6 to 11% of wet mass at peak lactation and then dec reased as pups approached weaning age. Total milk energy output until pups began to forage was 3609 kJ. Milk levels of Mg, Fe, Ca, K, and Na averaged 0.55 +/- 0.26, 0.23 +/- 0.2, 8.75 +/- 4.17, 5.42 +/- 2.11, a nd 9.87 +/- 4.3 mg.g(-1) dry matter, respectively. Of the minerals stu died, calcium appears to be most limiting in this species. The high de gree of variability in foraging time, milk composition and milk yield between individuals at the same stage of lactation could potentially y ield high variance in reproductive success among females of this polyg ynous species.