Variation in Milk Proteins Across Lactation in Pongo pygmaeus and Gorilla gorilla.

Milk is a critical nutrition source for all neonatal mammals. In addition to nutrition, milk contains a multitude of bioactive molecules that likely affect neonatal physiology, metabolism, and immune function. We suggest that changes in the milk proteome across lactation reflect the changing need of the neonate and juvenile offspring. We used mass spectrometry to characterize the milk proteomes from a Pongo pygmaeus (12 samples) and a Gorilla gorilla (6 samples) housed at the Smithsonian's National Zoo and Conservation Biology Institute and trained to give milk samples. We found a total of 454 proteins from P. pygmaeus and 428 proteins from G. gorilla. We specifically characterized changes across lactation in 13 proteins representing multiple compartments of milk, including the milk fat globule membrane and whey. Additionally, we characterized changes in various immunoglobulin types, finding similarities to previously published studies on primate milks. Despite broad similarities between the milk proteomes of these two apes, we demonstrated that proteomes from samples from 8 to 12 months clustered by species/individual and were distinct. Samples from more individuals are required to distinguish whether our result demonstrates species differences or individual differences. This study represents a baseline study that other zoo-based milk studies can build from. All RAW data, MetaMorpheus search results, and PAW_BLAST results are available on MassIVE at ftp://massive.ucsd.edu/MSV000089723/.