Changeover from signalling to energy-provisioning lipids during transition from colostrum to mature milk in the giant panda (Ailuropoda melanoleuca)
Among the large eutherian ( placental) mammals, ursids (bears) give birth to the most altricial neonates with the lowest neonatal:maternal body mass ratios. This is particularly exemplified by giant pandas in whom the transition from colostrum to main-phase lactation is unusually prolonged. To examine whether there is compensation for the provision of developmentally important nutrients that other species groups may provide in utero, we examined colostrum and milk lipids from birth until the transition was complete. Lipids known to be developmental signals or their precursors, and those that are fundamental to nervous system construction, such as docosahexaenoic acid (DHA) and phosphatidylserines containing DHA, appear early and then fall dramatically in concentration to a baseline at about 20 days. This also applies to other signalling lipids such as lysophosphatidylserines. The dynamics of lysophosphatidic acid and eicosanoids display a similar pattern, albeit less clearly and with differences between mothers. Triglycerides occur at relatively low levels initially and then increase in concentration with time post-partum until a plateau is reached at about 30 days or later. These patterns indicate an early provision of signalling lipids and their precursors, and lipids crucial to brain, retinal and central nervous system construction, followed by a changeover to lipids for energy metabolism. Thus, in giant pandas, and possibly among ursids in general, lactation is adapted to provisioning a highly altricial neonate to a degree that approximates to an extension of gestation.