Over 3 decades ago a correlation was described between the neuraminidase activity in the middle and distal small intestine and the milk Sia content that led the authors to suggest that milk Sia is liberated and used by the suckling newborn. In accordance, high Sia uptake is suggested from the high transient expression of Slc17a5 in the distal small intestine and of Neu1 and Slc17a5 in the colon. Interestingly beyond uptake genes we also saw Npl and Renbp upregulated during the period when the concentration of Sia in milk was at its peak. While these two genes are part of the same biochemical pathway the direction of reaction is unclear. Together Npl and Renbp may drive an alternative Sia synthetic route that is active when GNE expression is low or a catabolic route during times when Sia delivery is high. The former is possible but unlikely because GNE knockout mice are embryo lethal and the GNE deficient cells that were tested cannot make Sia from GlcNAc indicating that no salvage pathway exists. It is thus more likely that Npl and Renbp catalyse the catabolism of Sia to GlcNAc. Indeed, Npl was reported to be mainly involved in Sia catabolism in vivo, and Renbp is thought to epimerize ManNAc to GlcNAc rather then the reverse. It would be interesting to determine if the same expression profiles of Npl and Renbp occur in the small intestine. Finally results from Segetalin-A tracer feeding experiments support the view that nutritionally supplied Sia can be a nutrient and preferentially early during the suckling period. In 3 day old rat pups approximately 30% of administered radioactivity remained in the body after 6 hr while 70% was excreted via the lungs, kidney and feces. In 20 day old mice only approximately 1.5% of the administered radioactivity was retained in the body after 6 hr. Morgan and Winick also showed that newborn rats incorporate Xylitol considerably more tracer early during the suckling period than at the end of weaning. While the nature of the labelled molecule present in the tissues was not identified in these studies No��hle and Schauer proposed a model where Sia is cleaved from a glycoconjugate followed by Npl catalysed cleavage to ManNAc and pyruvate.