Changes in the Milk Metabolome of the Giant Panda (Ailuropoda melanoleuca) with Time after Birth – Three Phases in Early Lactation and Progressive Individual Differences

Abstract

Ursids (bears) in general, and giant pandas in particular, are highly altricial at birth. The components of bear milks and their changes with time may be uniquely adapted to nourish relatively immature neonates, protect them from pathogens, and support the maturation of neonatal digestive physiology. Serial milk samples collected from three giant pandas in early lactation were subjected to untargeted metabolite profiling and multivariate analysis. Changes in milk metabolites with time after birth were analysed by Principal Component Analysis, Hierarchical Cluster Analysis and further supported by Orthogonal Partial Least Square-Discriminant Analysis, revealing three phases of milk maturation: days 1–6 (Phase 1), days 7–20 (Phase 2), and beyond day 20 (Phase 3). While the compositions of Phase 1 milks were essentially indistinguishable among individuals, divergences emerged during the second week of lactation. OPLS regression analysis positioned against the growth rate of one cub tentatively inferred a correlation with changes in the abundance of a trisaccharide, isoglobotriose, previously observed to be a major oligosaccharide in ursid milks. Three artificial milk formulae used to feed giant panda cubs were also analysed, and were found to differ markedly in component content from natural panda milk. These findings have implications for the dependence of the ontogeny of all species of bears, and potentially other members of the Carnivora and beyond, on the complexity and sequential changes in maternal provision of micrometabolites in the immediate period after birth.

Changeover from signalling to energy-provisioning lipids during transition from colostrum to mature milk in the giant panda (Ailuropoda melanoleuca)

“…Their clustering around zero on the vertical axis indicates that their compositions are similar to one another. In contrast, the wider scatter on the vertical axis after day 7 indicates progressive, rapid, and approximately simultaneous divergence among individual mothers, as noted previously for other milk components10.…”

“…The main changeover, like that which we demonstrated for the protein, oligosaccharide, and metabolome profiles910, occurs between twenty and thirty days. Importantly, lipids such as PUFAs that are considered to be crucial for brain growth and for developmental and immune signalling are present at their highest levels only very early in lactation, while those needed predominately for energy generation and membrane construction appear later.…”

“…Second, the mixture of components of ursine colostrum may be unusual if not unique among eutherian mammals. Our examination of proteomics and metabolomics have upheld this hypothesis910. The objective for the study reported here was to test whether these predictions hold true for lipids, particularly given the special roles lipids have in development.…”

“…We here take the colostrum phase to end when all the major components of milk reach an approximate steady state, although slight modifications in composition may still occur during the main phase. By this definition, the colostrum period of giant pandas ends at about 30 days910, which is considerably longer than is known for any other eutherian, and stands in stark contrast to the less than 24 hours in, for example, Atlantic grey seals (A. Lowe, P. Pomeroy, D.G. Watson, M.W.…”

“…The changeover and maturation process of these profiles takes approximately thirty days to complete, over which period certain species of oligosaccharide disappeared, whilst others appeared. Further detail was added in a second study, in which a broad-spectrum metabolomics approach discerned three phases in the transition from colostrum to mature lactation10. The milks of different mothers in that study were at first similar in composition, then diverged after about seven days.…”