Interspecific and intraspecific variation in proximate, mineral, and fattyacid composition of milk in old world fruit bats (Chiroptera : Pteropodidae)

We examine the effect of body mass on milk composition among Old World frui t bats, including Pteropus pumilus (0.175 kg), Pteropus rodricensus (0.265 kg), Pteropus hypomelanus (0.571 kg), and Pteropus vampyrus (1.133 kg). We describe intra- and interspecific differences in the proximate composition of milk among these four species and the minerals and fatty acids in the mi lk of the latter two species. There were no differences between species in the concentrations of dry matter, fat, or lactose in milk. However, there w ere significant, although small, differences in the protein content of milk among species, with protein being significantly greater in P. rodricensus than in P. pumilus and P. hypomelanus and protein being significantly less in P. hypomelanus than in P. rodricensus and P. vampyrus. There were no dif ferences in mineral content between P. hypomelanus and P. vampyrus in milk minerals, but minor differences were evident in fatty acids 12:0, 14:0, 18: 0, 18:1n11, and 18:2n6. Our findings suggest that milk composition is relat ively constant across lactation for most proximate, mineral, and fatty acid components. We found a significant increase in dry matter and energy acros s lactation in the concentration of dry matter and energy in P. pumilus and fat in P. hypomelanus. In P. hypomelanus, we found a significant increase in the concentration of fatty acids 10:0 and 20:1n9 and a significant decre ase in Iso15 and 20:1n7. No other differences associated with day of lactat ion were found. These findings suggest that milk composition is generally s imilar within the genus Pteropus, despite a 6.5-fold difference in body mas s between species that we evaluated.