The composition of Australian fur seal (Arctocephalus pusillus doriferus) milk throughout lactation

The proximate chemical composition of milk was determined throughout lactat ion in the Australian fur seal (Arctocephalus pusillus doriferus Wood Jones ), a temperate species with an 11-mo lactation period typical of most tempe rate otariids. Average lipid and protein contents were 42% and 10%, respect ively, which is similar to that recorded for the polar otariid species but higher than reported in other temperate, long-lactation species. Milk compo sition, however, varied substantially throughout lactation, with lipid cont ent rising from 30% soon after parturition to 50% at 230 d postpartum befor e decreasing to 45% toward weaning. The trend in water content was opposite to that of lipid, while protein content increased only slightly during lac tation from 10% to 12%. The peak in lipid content occurred at approximately 70% of the way through lactation, similar to that found in the Australian sea lion and several phocid seal species. Significant positive relationship s were found between milk lipid content and both the duration of the preced ing foraging trip and body mass. A highly significant and close correlation was found between milk water and lipid contents such that gross energy con tent may be accurately predicted from water content alone. Similar predicti ve equations have been found for several other otariid and phocid species, but these appear to differ between phylogenetic groups.