New Insights into Porcine Milk N-Glycome and the Potential Relation with Offspring Gut Microbiome

N-Glycans are an important source of milk oligosaccharides. In addition to free oligosaccharides found in milk, N-glycans can also be utilized by gut microbes. A potential for milk N-glycans to act as gut microbe regulators in suckling animals has attracted considerable attention; however, sow milk N-glycans and their potential effects upon the piglet's gut microbes in vivo remain unknown. In the present study, we profiled the milk N-glycans of Meishan and Yorkshire sows during lactation using UPLC and a mass spectrometry-based glycome method, and we explored the correlations between milk N-glycans and offspring gut microbiota. Twenty-two N-glycan structures were identified in sow milk, among which 36% (8 out of 22) were fucosylated, 41% (9 out of 22) were sialylated, and 14% (3 out of 22) were high mannosylated. An N-glycan with a NeuGc structure (namely PNO20, GlcNAc4-Man3-Gal2-Fuc-Neu5Gc) was identified in sow milk for the first time. No compositional differences between the two breeds or between different lactation times were found in porcine milk N-linked oligosaccharides (PNOs); however, the abundances of different structures within this class did vary. The relative abundances of fucosylated PNO3 (GlcNAc4-Man3-Fuc) and sialylated PNO18 (GlcNAc4-Man3-Gal2-NeuAc) increased during lactation, and Meishan sows demonstrated a higher (P < 0.05) abundance of mannosylated PNO10 (GlcNAc2-Man6) and sialylated PNO17 (GlcNAc5-Man3-Gal-NeuAc) than Yorkshire sows. Apparent correlations between milk N-glycans and offspring gut microbial populations were found; for example, mannosylated PNO21 (GlcNAc2-Man9) was positively correlated with OTU706 (Lactobacillus amylovorus) and OTU1380 (Bacteroides uniformis). Overall, our results indicate that the milk N-glycome of Meishan and Yorkshire sows differs in N-glycome characteristics and that this is correlated to abundances of certain piglet gut microbes. These findings provide a reference for future elucidation of the involvement of gut microbes in milk N-glycan metabolism, which is important to the health both of large domestic animals and humans.