Sialyllactose occurs as free lactones in ovine colostrum.

Three sialyl oligosaccharide fractions were separated from ovine colostrum by gel filtration, anion exchange chromatography and normal-phase HPLC. They were characterized by 1H-NMR spectrometry as follows: Neu5Acalpha2-->3Galbeta1-->4Glc, Neu5Gcalpha2-->6Galbeta1-->4Glc and three forms of Neu5Gcalpha2-->3Galbeta1-->4Glc, namely Neu5Gcalpha2-->3Galbeta1-->4Glc itself, its lactone derivative between the carboxyl group of Neu5Gc and Gal OH-2 and another lactone derivative between the carboxyl group and Gal OH-4. In this study, Neu5Gc-lactose lactones, in their free form, have been isolated for the first time from any natural sources including milk or colostrum.