Proximate Composition of Australian Sea Lion Milk Throughout the Entire Supra-Annual Lactation Period

Abstract

A total of 87 milk samples was collected from 47 Australian sea lions, Neophoca cinerea, with pups ranging from one day old to 471 days old. Analysis of proximate composition yielded an overall mean (+/- s.d.) of 30.82 +/- 9.84% lipid, 56.97 +/- 9.96% water, 9.97 +/- 2.52% protein, and 0.88 +/- 0.25% ash. Milk fat content increased during lactation and was inversely proportional to water content. There was a significant difference between the lipid content of milk collected during the first half of lactation (<250 days, range 1-120 days) (26.1 +/- 8.7%, n = 35) and that collected during the second half of lactation (>250 days, range 314-469 days) (39.1 +/- 5.5%, n = 12) (Mann-Whitney U-test, P < 0.0001). The relatively low lipid (energy) content of Australian sea lion milk is postulated to be, in part, an adaptive response to living in a low-energy marine environment where the rate of energy transfer from mother to young is decreased and the duration of maternal dependence of the young is increased.